US20090056371A1

US20090056371A1 - Method and Apparatus for Deriching a Stream of Liquefied Natural Gas

Info

Publication number: US20090056371A1
Application number: US11/886,801
Authority: US
Inventors: Paramasivam Senthil Kumar
Original assignee: Individual
Current assignee: Shell USA Inc
Priority date: 2005-03-22
Filing date: 2006-03-20
Publication date: 2009-03-05
Also published as: EP1861671B1; RU2386091C2; RU2007138916A; WO2006100218A1; JP2008535961A; ES2561808T3; JP5411496B2; EP1861671A1

Abstract

The present invention relates to a method of deriching a stream of liquefied natural gas by extracting a natural gas liquid comprising inter alia the steps of: heating the stream of liquefied natural gas (1) in a first heat exchanger arrangement (5); splitting it into at least a first portion (17) and a second portion (19); passing the first portion (17) to a distillation column (21) and passing the second portion (19) to a second heat exchanger arrangement (26) and then supplying it (20) to the distillation column (21) from which a natural gas liquid stream (35) and an overhead vapour stream (40) are withdrawn; —passing the overhead vapour stream (40) to the second heat exchanger arrangement (26) to form an intermediate deriched condensate stream (49) of which at least a portion is thereafter passed to the distillation column.

Description

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for deriching a stream of liquefied natural gas (LNG) by extracting a natural gas liquid from the stream of liquefied natural gas. The resulting stream of deriched liquefied natural gas can be in liquid and/or vapour phase for instance utilizing subsequent regasification.
The term deriching is used in the present specification and claims as an opposite term for enriching, and is understood to include a meaning of removing hydrocarbon compounds higher than methane, i.e. “stripping” or “making leaner”. The term natural gas liquid is understood to include hydrocarbon compounds higher than methane, including ethane, ethylene, propane, propylene, butane and isomeric variations thereof, and butylenes and isomeric variations thereof.

BACKGROUND OF THE INVENTION

In addition to methane, liquefied natural gas typically contains higher hydrocarbon compounds including ethane, propane, and various isomeric forms of butane. These additional compounds have higher heating values than methane. Different specifications of liquefied natural gas, in particular with regard to heating value, are demanded in various markets.
In order to conform to pipeline specifications having a lower heating value, there can thus be a need for deriching a liquefied natural gas stream at a regasification facility before sending the regasified stream into the grid. One way of deriching is formed by recovery of natural gas liquids from the liquefied natural gas stream.
U.S. Pat. No. 6,604,380 discloses such a method for the recovery of natural gas liquids. In the disclosed method, a liquefied natural gas feed stream is split. With particular reference to FIG. 2 of the mentioned US patent, one portion of the split stream is heated in a heat exchanger whereby it is partially vapourised and then fed to a feed separator. A natural gas liquid rich bottom stream is removed from the feed separator and routed to a second separation method including a stabilizer. The other portion of the split stream bypasses the heat exchanger and is fed at a very low temperature of around −157° C. (−250° F.) as an external reflux into the second separation method. The methane-rich overhead vapour streams are drawn from the feed separator and the stabilizer, and combined and directed through the heat exchanger where it is cooled against the one portion of the split feed stream.
WO 2004/109180 discloses a method of processing LNG in a plant in which a heat source vaporizes pressurized LNG which is subsequently expanded to produce work in an open power cycle.
It has been found that the above-described methods are unnecessarily inefficient.

SUMMARY OF THE INVENTION

It is an object of the present invention to minimize the above problem.
It is a further object of the present invention to provide an alternative method for deriching a stream of liquefied natural gas.
One or more of the above and other objects may be achieved according to the present invention by providing a method of deriching a stream of liquefied natural gas by extracting a natural gas liquid from the stream of liquefied natural gas, the method at least comprising the steps of:
heating a feed stream containing the stream of liquefied natural gas in a first heat exchanger arrangement to form an intermediate feed stream;
splitting the intermediate feed stream into at least a first portion and a second portion;
passing the first portion to a distillation column and feeding it via a first feeding point;
passing the second portion to a second heat exchanger arrangement wherein it is further heated, and then supplying it to the distillation column via a second feeding point;
withdrawing a liquid stream containing the natural gas liquid from a lower portion of the distillation column;
withdrawing an overhead vapour stream from an upper portion of the distillation column;
passing the overhead vapour stream to the second heat exchanger arrangement where it is cooled against the second portion of the intermediate feed stream to form an intermediate deriched stream of which at least a portion is thereafter passed to the first heat exchanger arrangement and further cooled against the feed stream to form a product stream of deriched natural gas;
wherein during cooling of the overhead vapour stream in the second heat exchanger arrangement it is partially condensed to form an intermediate condensate, of which at least a portion is passed to the distillation column via a third feeding point, and an intermediate vapour which is passed to the first heat exchanger arrangement.
An advantage of the present invention is that it provides more flexibility in choosing the temperature profile in the distillation column, which facilitates efficient control of the method conditions in the distillation column.
Further it has been found that the use of the intermediate deriched stream to generate a reflux stream improves the natural gas liquid recovery significantly. The overhead vapour stream from the distillation column is partially condensed during the cooling in the second heat exchanger arrangement and the intermediate deriched stream comprises an intermediate condensate which can be passed to the distillation column via the third feeding point, and an intermediate vapour which can be passed to the first heat exchanger arrangement.
A further advantage is that the intermediate condensate is enriched in heavier components including natural gas liquids. Instead of submitting this condensate to the first heat exchanger arrangement it is re-submitted to the distillation column as an internal reflux. Hence the recovery of the natural gas liquid is significantly improved.
By choosing the relative cooling in the first and second heat exchanger arrangements, an intermediate temperature can be chosen in the intermediate deriched stream that allows to tailor the composition of the condensate.
Another advantage of the invention is that the heating and cooling upstream respectively downstream of the distillation column is performed in at least two stages. The resulting intermediate streams between the at least two stages are thus available for use in the method in addition to the fully heated respectively cooled streams.
One way of utilizing the intermediate feed stream is as an external reflux having a temperature that is lower than that of the portion being fed to the distillation column via the second feeding point but not as low as that of the original feed stream.
It has been found that an external reflux stream having a temperature as low as of liquefied natural gas (approximately of around −157° C., or less than −140° C.) is not generally required for an efficient separation of natural gas liquid components from liquefied natural gas. An advantage of the invention is that the temperature of the external reflux can be chosen higher than the temperature of the feed stream, for instance higher than −140° C. As a consequence, equipment such as the distillation column or a reboiler (if provided), can be smaller sized, and less power needs to be dissipated in a reboiler. The high-quality cold in the feed stream thus becomes available fully for recondensating the deriched natural gas.
Depending on the amount of heating applied in the first heat exchanger arrangement and the pressure of the feed stream, the intermediate feed stream can either be fully liquid or partly vapourized.
Where the heating of the feed stream in the first heat exchanger arrangement comprises partly vapourizing the feed stream whereby the intermediate feed stream comprises a mixture of liquid intermediate feed fraction and vaporous intermediate feed fraction, it is advantageous to split at least the liquid intermediate feed fraction into at least the first and second portions. The vaporous intermediate feed fraction, because of it relatively low temperature compared to the temperature after the second heating, is already relatively lean from natural gas liquids and does not have to be further distilled. It can be mixed in with a final product stream.
In a further aspect the present invention provides a deriched natural gas stream obtained by the method according to the present invention as well as an apparatus suitable for performing the method according to the present invention.
Preferred embodiments for the apparatus are derivable from preferred embodiments of the method and/or from the detailed description of embodiments set out below.
The above-described features and other features of the present invention will be further illustrated by way of example and with reference to the accompanying non-limiting drawing.

BRIEF DESCRIPTION OF THE DRAWING

In the accompanying drawing:

FIGS. 1 and 2 schematically show process flow schemes and apparatus not containing all features of the present invention but incorporated for illustration purposes;

FIG. 3 schematically shows a process flow scheme and apparatus according to the present invention; and

FIG. 4 schematically shows a preferred embodiment of the present invention wherein the process scheme of FIG. 2 is combined with the process scheme of FIG. 3.

For the purposes of this description, like reference numerals correspond to like parts. Reference numerals corresponding to lines are also used to refer to the respective streams carried in these lines.

DETAILED DESCRIPTION OF DRAWINGS

FIG. 1 schematically shows an apparatus for deriching a stream of liquefied natural gas by extracting a natural gas liquid from the stream of liquefied natural gas. A feed line 1 is connectable to a source of the liquefied natural gas. An optional pump 3 is provided in the feed line 1, of which the high-pressure outlet is in fluid communication with a first heat exchanger arrangement 5 via line 2.
An intermediate feed line 7 fluidly connects a first outlet 6 of the first heat exchanger arrangement 5 with a distributor 14. The distributor 14 has two outlets connected to lines 17 and 19. If desired, the distributor 14 may have more than two outlets. Line 17 connects to a distillation column 21 via an optional first control valve 23 and a first feeding point 25 provided in an upper part of the distillation column 21. The other line, line 19, also connects to the distillation column 21 but via a second heat exchanger arrangement 26, line 20, which can be optionally provided with a second control valve 27, and a second feeding point 29. This way, the first outlet 6 of the first heat exchanger arrangement 5 is in fluid communication with the second heat exchanger arrangement 26. Line 17 bypasses the second heat exchanger arrangement 26. The second feeding point 29 of the distillation column 21 is preferably located gravitationally lower than the first feeding point 25.
The distillation column 21 has a lower portion provided with a discharge opening 31 for withdrawing a liquid stream 35 from the distillation column 21. An optional reboiler 33 may be provided in line 35 connecting to the discharge opening 31. A reboil return line 37 feeds back from the reboiler 33 into the lower portion of the distillation column 21. The optional reboiler 33 may be integrated with the distillation column 21 instead of the shown external arrangement. A line 38 connects to line 35 or to the optional reboiler 33 for discharging the natural gas liquid.
The distillation column 21 also has an upper portion provided with an overhead vapour outlet 39. The overhead vapour outlet 39 is in fluid communication with the first heat exchanger arrangement 5 via the second heat exchanger arrangement 26. Line 40 extends between the overhead vapour outlet 39 and the second heat exchanger arrangement 26, and is connected to line 48 that extends between the second heat exchanger arrangement 26 and the first heat exchanger arrangement 5, and is connected to line 55 downstream of the first heat exchanger arrangement 5 via a second outlet 41 of the first heat exchanger arrangement 5.
An optional pump 65 can be included in line 55, which discharges into line 67, for increasing the pressure to produce a deriched liquefied natural gas stream at a pressure according to a local specification. Line 67 can be connected to any type of re-gasification system, including systems known from an article “Innovative gas processing with various LNG sources” by Joseph Cho et al, as published in LNG Journal January/February 2005 pp 23-27, the content of which is herewith incorporated by reference.
The above-described apparatus is capable of deriching a stream of liquefied natural gas by extracting a natural gas liquid from the stream of liquefied natural gas. An optional bypass line 59 can be provided to fluidly connect line 1 or the high-pressure outlet of pump 3 upstream of the first heat exchanger arrangement 5 with line 55 downstream of the first heat exchanger arrangement 5. The optional bypass line 59 can be provided with a control valve 61. With the bypass line 59 the deriching arrangement can be bypassed and the extraction of the natural gas liquid avoided.
In operation, the apparatus of FIG. 1 works as follows. A feed stream containing the stream of liquefied natural gas is supplied via feed line 1 and heated in the first heat exchanger arrangement 5 against an intermediate deriched stream in line 48 to form an intermediate feed stream 7. Before supplying the feed stream 1 to the heat exchanger arrangement 5 it can be pressurized or its pressure increased using the optional pump 3. This is particularly useful when the liquefied natural gas is supplied at atmospheric pressure or near atmospheric pressure.
The intermediate feed stream 7 is split in the distributor 14 into at least a first portion 17 and a second portion 19. The first portion 7 is passed to the distillation column 21 and fed into it via the first feeding point 25. Pressure and temperature can be controlled utilizing control valve 23.
The second portion 19 of the intermediate feed stream 7 is passed to the second heat exchanger arrangement 26 wherein it is further heated, against an overhead stream in line 40. The resulting further heated stream is then supplied to the distillation column 21 via line 20 and the second feeding point 29. Pressure can be controlled employing control valve 27.
During the further heating in the second heat exchanger arrangement 26 the second portion 19 of the intermediate feed stream 7 is at least partially vapourised. It is generally recommended to vapourize to a molar fraction of at least 60%.
As the temperature of the first portion 17 can be lower than that of the second portion 19, the first portion 17 acts as an external reflux stream in the distillation process. It helps scrubbing the natural gas liquid from vapour generated from the second portion 19 as well as in optional reboiler 33. The scrubbing is facilitated by the preference that the first feeding point 25 is located gravitationally higher than the second feeding point 29.
A liquid stream containing the natural gas liquid is then withdrawn from a lower portion of the distillation column 21 via the discharge opening 31 into line 35. Optionally, the liquid stream is heated and partly fed back via line 37 to the lower portion of the distillation column 21 to allow some vapour to form containing relatively lighter molecules. The remainder is discharged as natural gas liquid into line 38.
On the other side of the distillation column 21, an overhead vapour stream 40 is withdrawn from an upper portion of the distillation column 21. The overhead vapour stream 40 is a deriched stream containing mainly methane and sometimes also other components such as for instance ethane and a remainder of propane.
The overhead vapour stream 40 is passed to the second heat exchanger arrangement 26 where it is cooled against the intermediate feed stream to form an intermediate deriched stream 48 of which at least a portion is thereafter passed to the first heat exchanger arrangement 5 and further cooled against the feed stream 1 to form a product stream 55 of deriched natural gas. The product stream 55 can be fully re-condensed.
Optionally, the product stream 55 is combined with a bypass stream drawn from the feed stream 2 via line 59. The pressure of the product stream in line 55 can then be raised to a desired pressure level by means of the optional pump 65, which is generally more energy efficient as the stream in line 55 generally tends to be fully condensed. The product stream is discharged through line 67 after which it can be further processed (not shown), for instance including re-gasification by heating it to convert it into a gaseous stream. Several possible re-gasification methods are described in the article from the LNG Journal January/February 2005 already introduced.
Although not strictly required, an optional compressor (not shown) can be provided in line 40 to be able to generate a comfort margin in the pressure to ensure that the product stream in line 55 leaving the first heat exchanger arrangement 5 at outlet 41 is not only fully re-condensed but also sub-cooled to a sufficient degree. This is of less importance when a substantial amount of the feed stream 2 is allowed to bypass via line 59, as in that case the product stream leaving the first heat exchanger arrangement 5 is subjected to direct heat exchange.
An advantage of having two heat exchanger arrangements 5, 26 is that the intermediate streams 7 and/or 48 are now available for use in the process. In the embodiment of FIG. 1, a portion (first portion 17) of the intermediate stream 7 is utilized as external reflux having a temperature that is lower than that of the portion (second portion 19) being fed to the distillation column 21 via the second feeding point 29 but not as low as the feed stream 1. By proper balance of the heating capacity in the first heat exchanger arrangement 5 versus the second heat exchanger arrangement 26, increased temperature control is achieved over the reflux stream 17 and the further heated feed stream 20, as compared to what is possible in the process as described in U.S. Pat. No. 6,604,380. This increased flexibility enables efficient control of the process conditions in the distillation column 21, to achieve desired separation between overhead stream 40 and bottom stream 38 of a selected natural gas liquid component.
FIG. 2 is based on the embodiment as shown and explained above with reference to FIG. 1 and shows a gas/liquid separator 9 (referred to in the claims as “second gas/liquid separator”) that is arranged in the connection between the first outlet 6 of the first heat exchanger arrangement 5 and the distributor 14. The gas/liquid separator is here provided in the form of a feed separation vessel 9. The first outlet 6 of the first heat exchanger arrangement 5 is connected with the feed separation vessel 9. The feed separation vessel 9 has a bottom outlet 11 and an overhead outlet 13. The bottom outlet 11 is connected to the distributor 14 via line 15. The overhead outlet 13 is fluidly connected to line 48 via line 57 upstream of the first heat exchanger arrangement 5.
The embodiment of FIG. 2 works as follows. As the feed stream is heated in the first heat exchanger arrangement 5, it can be partially vapourised. The vapour is drawn from the overhead outlet 13 and combined with the intermediate deriched stream in line 48. The combined streams are then further cooled and recondensed together in the first heat exchanger arrangement 5 against the feed stream 2.
As the temperature is still relatively low, the vapour will contain predominantly the leaner components such as methane. The components with higher heating values, such as propane will still be essentially fully in the liquid phase together with ethane and methane. The vapourised fraction does not have to be further distilled and can be mixed in with the distilled stream in line 48 to be recondensed in the first heat exchanger arrangement 5.
Typically, the molar fraction of vapour can be between 1 and 90%. The higher the molar fraction of vapour, the lower the mass load is on the extraction apparatus downstream. In this respect, for a typical liquefied natural gas composition it is preferred that at least 50 mol. % is in vapour phase. On the other hand, the higher the molar fraction of vapour the lower the recovery of natural gas liquids since the mass separation in the vessel is not as high as in the distillation column 21. In this respect, it is preferred that the molar fraction of vapour is not more than 80%.
The liquid that is drawn from the bottom outlet 11 of the separator 9 is led to the distributor 14, where part of it is sent to the distillation 21 column via line 17 as an external reflux thereby bypassing the second heat exchanger arrangement 26.
An advantage of this embodiment is that the external reflux is fully liquid so that it can be fully effective as scrubbing medium. The temperature of the external reflux is lower than that of the portion being fed to the distillation column via the second feeding point 29, but not as low as that of the original feed stream 1. The temperature can be controlled by choosing the amount of heat exchange in the first heat exchanger 5, optionally in co-dependence of controlling the amount of expansion in control valve 23.
An advantage of the optional control valves 23 and 27 is that the distillation column 21 is operated at a lower pressure than the feed separator 9, which improves the separation efficiency of natural gas liquid components in the column 21.
Still referring to FIG. 2, an optional overhead compressor 63 can be provided between the overhead vapour outlet 39 of the distillation column 21 and the second heat exchanger arrangement 26. Herewith the optional pressure drop over valves 23 and 27 can be compensated whereby the pressure in line 48 can be brought to the pressure level as set by the feed stream in line 7.
It is preferred to arrange the compressor 63 upstream of the second heat exchanger arrangement 26, because the overhead stream 40 is by virtue of the distillation column 21 always fully vaporous whereas downstream of the second heat exchanger arrangement 26 the product stream can be of a multi-phase nature.
Alternatively, an expansion device can be provided in line 57, such as a Joule-Thompson valve (not shown) to lower the pressure in line 57 to that in line 48. Now having the process schemes of FIGS. 1 and 2 explained, FIG. 3 shows an embodiment according to the present invention which is based on the embodiment as shown and explained above with reference to FIG. 1, wherein an internal reflux system is provided in the connection line 48 between the distillation column's overhead vapour outlet 39 and the first heat exchanger arrangement 5. The reflux system here shown comprises a gas/liquid separator (referred to in the claims as “first gas/liquid separator”) here provided in the form of a reflux separation vessel 43. The reflux separation vessel 43 is arranged downstream of the second heat exchanger arrangement 26 in line 48 and connected to the second heat exchanger arrangement 26 via line 42. The separator 43 has a bottom outlet 45 and an overhead outlet 47. The bottom outlet 45 is connected to the distillation column 21 via line 49 and a third feeding point 51 to provide a reflux stream. An optional control valve 53 can be provided in line 49. The third feeding point 51 is best arranged gravitationally higher than the second feeding point 29, as the temperature of the reflux stream 49 is generally lower than that of the further heated feed stream 20, and gravitationally lower than the first feeding point 25.
The overhead outlet 47 of the reflux separation vessel 43 is fluidly connected with the first heat exchanger arrangement 5 via line 48.
In operation, where a methane, ethane and propane containing feed stream of liquefied natural gas is fed into the process, a majority of the propane is recovered in distillation column 21. The selective recovery of propane can be increased by allowing the residual propane components that may be present in the overhead vapour stream 40 to condense in the second heat exchanger arrangement 26. The intermediate condensate 49 is drawn from the reflux separation vessel 43 and fed back into the distillation column 21 as a cold reflux stream. The propane has another chance of leaving the process via outlet 31.
Since the second heat exchanger arrangement 26 brings the intermediate deriched stream only to an intermediate temperature, the mass selectivity of the reflux stream can be tailored by choice of that temperature, and optionally also the pressure drop in optional valve 53. Herewith it can be avoided that methane or ethane is unnecessarily circulated through the column thereby merely consuming energy but not increasing the production of deriched natural gas leaving the process via line 55.
While comparing the process scheme of FIG. 1 (not containing all the features of the present invention) and the process scheme of FIG. 3 (according to the present invention), calculations predicting the recovery of propane have shown that the process scheme of FIG. 1 under given process conditions resulted in a propane recovery of 69%, whilst under the same given process conditions the process scheme of FIG. 3 resulted in a propane recovery of 90%.
Typically, the molar fraction of vapour can be between 50 and 95%. The higher the molar fraction of vapour, the better the lesser the quantity of leaner components circulated in the reflux loop. In this respect, it is preferred that at least 60 mol. % is in vapour phase. On the other hand, the higher the molar fraction of vapour the lower the recovery of natural gas liquids since less of the natural gas liquid components are recondensed and fed back into the distillation column 21. In this respect, for most typical liquefied natural gas compositions it is preferred that the molar fraction of vapour is not more than 90%.
FIG. 4 shows a preferred embodiment according to the present invention, wherein the processes and apparatuses as illustrated in FIGS. 2 and 3 are combined. For a description of the details, reference is made to the above descriptions of FIGS. 1, 2, and 3.
The following Table I shows recommended lower and upper limits of temperatures and pressures of the streams through various lines in the process, as well as a typical value of temperature and pressure in a particular example of operation.

TABLE I

	T-low	T-up	T	P-low	P-up	P
Line	(° C.)	(° C.)	(° C.)	(bar)	(bar)	(bar)

1	−162	−120	−161	1.0	1.5	1.1
2	−162	−120	−161	5	50	33
7, 15, 17, 57	−140	−50	−81	5	50	33
20	−70	−20	−37	5	50	33
38	−10	150	90	2	45	29
40	−90	−10	−28	2	45	29
42, 48, 49	−60	−30	−49	5	50	33
55	−110	−162	−128	5	50	33
66	−40	0	−19	5	50	33
67	−110	−162	−140	20	140	70

In the example to which Table I relates, the molar fraction of vapour in line 7 was 66%, and in line 42 it was 69%. The molar fraction of vapour in line 20 was 75%. It has been predicted on the basis of mass-balance calculations that the apparatus and process of FIG. 4 provide an efficient means for recovering natural gas liquid components from the liquefied natural gas feed stream in excess of 90%.
In the context of the present specification, the heat exchanger arrangements can comprise one heat exchanger, or a plurality of heat exchangers in parallel and/or in series.

Claims

1. A method of deriching a stream of liquefied natural gas by extracting a natural gas liquid from the stream of liquefied natural gas, the method at least comprising the steps of:

heating a feed stream containing the stream of liquefied natural gas in a first heat exchanger arrangement to form an intermediate feed stream;

splitting the intermediate feed stream into at least a first portion and a second portion;

passing the first portion to a distillation column and feeding it via a first feeding point;

passing the second portion to a second heat exchanger arrangement wherein it is further heated, and then supplying it to the distillation column via a second feeding point;

withdrawing a liquid stream containing the natural gas liquid from a lower portion of the distillation column;

withdrawing an overhead vapour stream from an upper portion of the distillation column;

passing the overhead vapour stream to the second heat exchanger arrangement where it is cooled against the second portion of the intermediate feed stream to form an intermediate deriched stream of which at least a portion is thereafter passed to the first heat exchanger arrangement and further cooled against the feed stream to form a product stream of deriched natural gas;

wherein during cooling of the overhead vapour stream in the second heat exchanger arrangement it is partially condensed to form an intermediate condensate, of which at least a portion is passed to the distillation column via a third feeding point, and an intermediate vapour which is passed to the first heat exchanger arrangement.

2. The method of claim 1, wherein said heating of the feed stream in the first heat exchanger arrangement comprises partly vapourizing the feed stream whereby the intermediate feed stream comprises a mixture of liquid intermediate feed fraction and vaporous intermediate feed fraction; and wherein at least the liquid intermediate feed fraction is split into at least the first and second portions.

3. The method of claim 2, wherein the mixture is passed to a feed separating vessel from which the liquid intermediate feed fraction and the vaporous intermediate feed fraction are respectively drawn before splitting it into the at least first and second portions.

4. The method of claim 1, wherein the second feeding point is located gravitationally lower than the first feeding point.

5. The method of claim 1, wherein the third feeding point is gravitationally lower than the first feeding point.

6. The method of claim 1, wherein the third feeding point is gravitationally higher than the second feeding point.

7. The method of claim 1, wherein the overhead vapour stream is compressed before passing it to the second heat exchanger arrangement.

8. The method of claim 1, wherein the product stream of de-riched natural gas is subsequently re-gasified.

9. A deriched liquefied natural gas stream obtained by the method of claim 1.

10. An apparatus for deriching a stream of liquefied natural gas by extracting a natural gas liquid from the stream of liquefied natural gas, the apparatus at least comprising:

a first heat exchanger arrangement arranged to receive a feed stream containing the stream of liquefied natural gas and provided with an outlet to discharge an intermediate feed stream;

a second heat exchanger arrangement in fluid communication with the outlet of the first heat exchanger arrangement;

a distillation column having at least first, second and third feeding points, a lower portion provided with a discharge opening for withdrawing a liquid stream containing the natural gas liquid, and an upper portion provided with an overhead vapour outlet in fluid communication with the first heat exchanger arrangement via at least the second heat exchanger arrangement;

a distributor connected to the outlet of the first heat exchanger arrangement, the distributor having a first outlet being connected to the first feeding point of the distillation column, and a second outlet being connected to the second feeding point of the distillation column via the second heat exchanger arrangement; and

a first gas/liquid separator downstream of the overhead vapour outlet and between the second heat exchanger arrangement and first heat exchanger arrangement, the first separator having an outlet connected to the third feeding point of the distillation column and an outlet in fluid communication with the first heat exchanger arrangement.

11. The apparatus of claim 10, further comprising a second gas/liquid separator having an inlet connected to the outlet of the first heat exchanger and a bottom outlet connected to the distributor.

12. The apparatus of claim 10, further comprising a compressor between the outlet of the distillation column and the second heat exchanger arrangement.

13. The method of claim 2, wherein the second feeding point is located gravitationally lower than the first feeding point.

14. The method of claim 3, wherein the second feeding point is located gravitationally lower than the first feeding point.

15. The method of claim 2, wherein the third feeding point is gravitationally lower than the first feeding point.

16. The method of claim 3, wherein the third feeding point is gravitationally lower than the first feeding point.

17. The method of claim 4, wherein the third feeding point is gravitationally lower than the first feeding point.

18. The method of claim 2, wherein the third feeding point is gravitationally higher than the second feeding point.

19. The method of claim 3, wherein the third feeding point is gravitationally higher than the second feeding point.

20. The method of claim 4, wherein the third feeding point is gravitationally higher than the second feeding point.