U.S. patent application number 12/438032 was filed with the patent office on 2010-07-01 for method and apparatus for treating a hydrocarbon stream.
Invention is credited to Eduard Coenraad Bras, Jill Hui Chiun Chieng, Akash Damodar Wani.
Application Number | 20100162753 12/438032 |
Document ID | / |
Family ID | 37831502 |
Filed Date | 2010-07-01 |
United States Patent
Application |
20100162753 |
Kind Code |
A1 |
Bras; Eduard Coenraad ; et
al. |
July 1, 2010 |
METHOD AND APPARATUS FOR TREATING A HYDROCARBON STREAM
Abstract
The present invention relates to a method of treating a
hydrocarbon stream, the method at least comprising the steps of:
supplying a partly condensed feed stream (10). to a first
gas/liquid separator (2) and into a gaseous stream (2 and a liquid
stream (30); expanding the liquid stream (30) and the gaseous
stream (20) and subsequently feeding them into a second gas/liquid
separator (3) at a first and second feeding point (32)
respectively, the second feeding point (32) being at a higher level
than the first feeding point (31); feeding a liquefied natural gas
stream (70,70b) into the second gas/liquid separator (3) at a third
feeding point (33) being at a higher level than the second feeding
point (32); removing from the top of the second gas/liquid
separator (3) a C2+ lean gaseous stream (60) and from the bottom a
liquid stream (80, 80a); wherein the liquefied natural gas stream
(70,70b) is obtained from a source (4) of liquefied natural gas
from a separate plant.
Inventors: |
Bras; Eduard Coenraad; (The
Hague, NL) ; Chieng; Jill Hui Chiun; (The Hague,
NL) ; Wani; Akash Damodar; (The Hague, NL) |
Correspondence
Address: |
SHELL OIL COMPANY
P O BOX 2463
HOUSTON
TX
772522463
US
|
Family ID: |
37831502 |
Appl. No.: |
12/438032 |
Filed: |
August 21, 2007 |
PCT Filed: |
August 21, 2007 |
PCT NO: |
PCT/EP2007/058648 |
371 Date: |
February 19, 2009 |
Current U.S.
Class: |
62/611 |
Current CPC
Class: |
F25J 2205/30 20130101;
F25J 2240/02 20130101; F25J 2210/62 20130101; F25J 2200/02
20130101; F25J 2205/04 20130101; F25J 3/0233 20130101; F25J
2270/904 20130101; F25J 3/0214 20130101; F25J 3/0238 20130101; F25J
3/0209 20130101 |
Class at
Publication: |
62/611 |
International
Class: |
F25J 1/00 20060101
F25J001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2006 |
EP |
06119358.7 |
Claims
1. Method of treating a hydrocarbon stream in a plant, the method
at least comprising the steps of: (a) supplying a partly condensed
feed stream to a first gas/liquid separator; (b) separating the
feed stream in the first gas/liquid separator into a gaseous stream
and a liquid stream; (c) expanding the liquid stream obtained in
step (b) and feeding it into a second gas/liquid separator at a
first feeding point; (d) expanding the gaseous stream obtained in
step (b), thereby obtaining an at least partially condensed stream,
and subsequently feeding it into the second gas/liquid separator at
a second feeding point, the second feeding point being at a higher
level than the first feeding point; (e) feeding a liquefied natural
gas stream into the second gas/liquid separator at a third feeding
point, the third feeding point being at a higher level than the
second feeding point; (f) removing from the top of the second
gas/liquid separator a C2+ lean gaseous stream; and (g) removing
from the bottom of the second gas/liquid separator a liquid stream;
wherein the liquefied natural gas stream as fed in step (e) is
obtained from a source of liquefied natural gas from a separate
plant.
2. Method according to claim 1, wherein the liquefied natural gas
stream has a temperature below -100.degree. C.
3. Method according to claim 1, wherein the gaseous stream obtained
in step (f) is sent to a gas network.
4. Method according to claim 1, wherein the gaseous stream obtained
in step (f) is not liquefied.
5. Method according to claim 1, wherein the gaseous stream obtained
in step (f) is heat exchanged against the feed stream.
6. Method according to claim 1, wherein the liquefied natural gas
stream as fed in step (e) has been previously heat exchanged
against the feed stream.
7. Method according to claim 1, wherein the liquid stream removed
from the bottom of the second gas/liquid separator is subjected to
fractionation thereby obtaining two or more products including
ethane.
8. Method according to claim 1, wherein >75 mole % of the ethane
present in the partially partly condensed feed stream is recovered
in the liquid stream obtained in step (g).
9. Method according to claim 1, wherein the pressure drop during
expanding in step (d) is less than 15 bar.
10. Method according to claim 1, wherein the pressure in the second
gas/liquid separator is from 15 to 40 bar.
11. Method according to claim 1, wherein the C2+ lean gaseous
stream removed from the top of the second gas/liquid separator in
step (f) is a gaseous stream comprising < (less than) 10 mole %
hydrocarbons having 2 or more carbon atoms.
12. Method according to claim 1, wherein the source of liquefied
natural gas from a separate plant is a liquefied natural gas
storage tank at a liquefied natural gas import terminal.
13. Apparatus for treating a hydrocarbon stream in a plant, the
apparatus at least comprising: a first gas/liquid separator having
an inlet for a partly condensed feed stream, a first outlet for a
gaseous stream and a second outlet for a liquid stream; a second
gas/liquid separator having at least a first outlet for a gaseous
stream and a second outlet for a liquid stream and first, second
and third feeding points, the third feeding point being at a higher
level in the gas/liquid separator than the second feeding point,
said second feeding point being at a higher level in the gas/liquid
separator than the first feeding point; a first expander for
expanding the gaseous stream obtained from the first outlet of the
first gas/liquid separator, the first expander having an outlet
which is connected to the second feeding point of the second
gas/liquid separator; and a second expander for expanding the
liquid stream obtained from the second outlet of the first
gas/liquid separator, the second expander having an outlet which is
connected to the first feeding point of the second gas/liquid
separator; wherein the third feeding point is connected to a source
of liquefied natural gas from a separate plant.
14. Apparatus according to claim 13 wherein the source of liquefied
natural gas from a separate plant is a liquefied natural gas
storage tank at a liquefied natural gas import terminal.
15. Method according to claim 2, wherein the gaseous stream
obtained in step (f) is sent to a gas network.
16. Method according to claim 2, wherein the gaseous stream
obtained in step (f) is not liquefied.
17. Method according to claim 3, wherein the gaseous stream
obtained in step (f) is not liquefied.
18. Method according to claim 2, wherein the gaseous stream
obtained in step (f) is heat exchanged against the feed stream.
19. Method according to claim 3, wherein the gaseous stream
obtained in step (f) is heat exchanged against the feed stream.
20. Method according to claim 4, wherein the gaseous stream
obtained in step (f) is heat exchanged against the feed stream.
Description
[0001] The present invention relates to a method and/or apparatus
of treating a hydrocarbon stream such as a natural gas stream.
[0002] Several processes and apparatuses for treating a hydrocarbon
stream are known. An example is given in US 2005/0268649 A1
relating to a process for processing natural gas or other
methane-rich gas streams to produce a liquefied natural gas (LNG)
stream that has a high methane purity and a liquid stream
containing predominantly hydrocarbons heavier than methane.
[0003] A problem of the known method is that it is rather
complicated thereby resulting in high capital expenses (CAPEX), but
at the same time it does not obtain a satisfactory recovery of in
particular ethane. Also the amount of fuel gas produced is not
optimal, because the focus of US 2005/0268649 A1 is mainly on the
liquefaction of natural gas rather than on the production of
`residual streams` and recovery of ethane therefrom.
[0004] A further problem of US 2005/0268649 A1 is that the start up
of the method or the plant for performing the method takes a
significant amount of time.
[0005] It is an object of the present invention to minimize one or
more of the above problems, while at the same time maintaining or
even improving the recovery of ethane and heavier hydrocarbons, in
particular ethane, from the hydrocarbon stream.
[0006] It is a further object of the present invention to provide
an alternative method for treating a natural gas stream.
[0007] The present invention provides a method of treating a
hydrocarbon stream such as a natural gas stream, in a plant, the
method at least comprising the steps of:
[0008] (a) supplying a partly condensed feed stream to a first
gas/liquid separator;
[0009] (b) separating the feed stream in the first gas/liquid
separator into a gaseous stream and a liquid stream;
[0010] (c) expanding the liquid stream obtained in step (b) and
feeding it into a second gas/liquid separator at a first feeding
point;
[0011] (d) expanding the gaseous stream obtained in step (b),
thereby obtaining an at least partially condensed stream, and
subsequently feeding it into the second gas/liquid separator at a
second feeding point, the second feeding point being at a higher
level than the first feeding point;
[0012] (e) feeding a liquefied natural gas stream into the second
gas/liquid separator at a third feeding point, the third feeding
point being at a higher level than the second feeding point;
[0013] (f) removing from the top of the second gas/liquid separator
a C2+ lean gaseous stream; and
[0014] (g) removing from the bottom of the second gas/liquid
separator a liquid stream;
[0015] wherein the liquefied natural gas stream as fed in step (e)
is obtained from a source of liquefied natural gas from a separate
plant.
[0016] In a further aspect the present invention relates to an
apparatus for treating a hydrocarbon stream such as a natural gas
stream, in a plant, the apparatus at least comprising:
[0017] a first gas/liquid separator having an inlet for a partly
condensed feed stream, a first outlet for a gaseous stream and a
second outlet for a liquid stream;
[0018] a second gas/liquid separator having at least a first outlet
for a gaseous stream and a second outlet for a liquid stream and
first, second and third feeding points, the third feeding point
being at a higher level in the gas/liquid separator than the second
feeding point, said second feeding point being at a higher level in
the gas/liquid separator than the first feeding point;
[0019] a first expander for expanding the gaseous stream obtained
from the first outlet of the first gas/liquid separator, the first
expander having an outlet which is connected to the second feeding
point of the second gas/liquid separator; and
[0020] a second expander for expanding the liquid stream obtained
from the second outlet of the first gas/liquid separator, the
second expander having an outlet which is connected to the first
feeding point of the second gas/liquid separator;
[0021] wherein the third feeding point is connected to a source of
liquefied natural gas from a separate plant.
[0022] Hereinafter the invention will be further illustrated by way
of example and with reference to the following non-limiting
drawing. In the drawing,
[0023] FIG. 1 schematically shows a process scheme in accordance
with the present invention.
[0024] For the purpose of this description, a single reference
number will be assigned to a line as well as a stream carried in
that line. Same reference numbers refer to similar components.
[0025] Embodiments of the present invention relate to the treatment
of a natural gas stream, and may involve recovery of at least some
of the ethane, propane, butanes and higher hydrocarbons such as
pentane from the natural gas. The recovery of hydrocarbons may be
done for several purposes. One purpose may be the production of
hydrocarbon streams consisting primarily of hydrocarbon products
heavier than methane such as natural gas liquids (NGLs; usually
composed of ethane, propane and butanes), liquefied petroleum gas
(LPG; usually composed of propane and butane) or condensates
(usually composed of butanes and heavier hydrocarbon components).
Another purpose may be the adjustment of e.g. the heating value of
the hydrocarbon stream to correspond to desired specifications of
sales gas.
[0026] It has been found that, using the surprisingly simple
methods set forth in the present disclosure, the CAPEX can be
significantly lowered. As an example no (partial) reflux of the
gaseous overhead stream from the second gas/liquid separator is
needed.
[0027] Further, also due to its simplicity, the methods and
apparatuses described herein are expected to be very robust and can
be started up quickly when compared with known line-ups.
[0028] Furthermore it has been found a high ethane recovery may be
obtained using the methods described herein. thereby resulting in a
leaner methane-rich natural gas stream. The methods have also been
contemplated to be suitable for feed streams having a pressure well
below 70 bar, at the same time maintaining a relatively high ethane
recovery.
[0029] Another advantage is that it is suitable for a broad range
of feed stream compositions.
[0030] A further advantage is that more sales gas is produced, in
particular if the overhead gas is not subsequently liquefied or
refluxed to the second gas/liquid separator (contrary to e.g. US
2005/0268649 A1).
[0031] The hydrocarbon feed stream may be any suitable
hydrocarbon-containing stream to be treated, but is usually a
natural gas stream which may be obtained from natural gas or
petroleum reservoirs. As an alternative the natural gas stream may
also be obtained from another source, also including a synthetic
source such as a Fischer-Tropsch process.
[0032] Usually the feed stream is comprised substantially of
methane. Preferably the feed stream comprises at least 60 mole %
methane, more preferably at least 80 mole % methane.
[0033] Depending on the source, the feed stream may contain varying
amounts of hydrocarbons heavier than methane such as ethane,
propane, butanes and pentanes as well as some aromatic
hydrocarbons. The feed stream may also contain non-hydrocarbons
such as H.sub.2O, N.sub.2, CO.sub.2, H.sub.2S and other compounds,
and the like.
[0034] Embodiments of the invention involve supplying a feed stream
to a first gas/liquid separator; separating the feed stream into a
gaseous stream and a liquid stream; and feeding these gaseous and
liquid streams into a second gas/liquid separator.
[0035] If desired, the feed stream containing the natural gas may
be pre-treated before feeding it to the first gas/liquid separator.
This pre-treatment may comprise removal of undesired components
such as CO.sub.2 and H.sub.2S, or other steps such as pre-cooling,
pre-pressurizing or the like. As these steps are well known to the
person skilled in the art, they are not further discussed here.
Preferably the hydrocarbon feed stream contains < (less than) 1
mole % CO.sub.2.
[0036] The first and second gas/liquid separator may be any
suitable means for obtaining at least a gaseous stream and a liquid
stream, such as a scrubber, distillation column, etc. If desired,
three or more gas/liquid separators may be present. Preferably the
second gas/liquid separator is a de-methanizer, i.e. the overhead
stream of the second gas/liquid separator being methane-enriched
and the bottom stream of the second gas/liquid separator being
ethane-enriched when compared with the hydrocarbon feed stream.
[0037] The gaseous and liquid streams may be expanded before
feeding them into the second gas/liquid separator. The person
skilled in the art will understand that the steps of expanding may
be performed in various ways using any expansion device (e.g. using
a throttling valve, a flash valve or a common expander).
[0038] Further, the person skilled in the art will readily
understand that treated hydrocarbon streams may be further
processed, if desired. Also, further intermediate processing steps
between the first and second gas/liquid separator may be
performed.
[0039] The invention provides methods and apparatuses wherein a C2+
lean gaseous stream is produced in a plant, whereby a liquefied
natural gas (LNG) stream is employed that is obtained from a source
of liquefied natural gas from a separate plant. In what may
hereinafter be referred to as step (e), the LNG stream may be fed
into the second gas/liquid separator.
[0040] Preferably the LNG stream has a temperature below
-100.degree. C. and is at least partially condensed and comprises
more than 60 mole % methane, preferably more than 80 mole %
methane. The phrase "source of liquefied natural gas from a
separate plant" means that the LNG is produced in a separate plant
from the plant in which the C2+ lean gaseous stream is produced. No
LNG stream is used that is generated in the hydrocarbon treating
plant of the invention, such as any LNG stream produced during the
treating itself or downstream of the treating (e.g. downstream of
the second gas/liquid separator). Thus, contrary to e.g. US
2005/0268649 A1, an already existing LNG stream is used that has
been produced elsewhere, for example an LNG stream produced in a
separate liquefaction plant. The separate source may be a storage
tank or a stream from a nearby liquefaction plant. Also, the LNG
stream may have been obtained from an offloading LNG carrier
vessel. Preferably the LNG stream is obtained from a separate plant
at an LNG import terminal, such as an LNG storage tank at an LNG
import terminal.
[0041] In a step (f), a gaseous stream is removed from the top of
the second gas/liquid separator. The gaseous stream obtained in
step (f) is a C2+ lean gaseous stream. By "C2+ lean" is meant a
gaseous stream which has a low proportion of hydrocarbons having
two or more carbon atoms, including a stream rich in methane, with
only a minor proportion of hydrocarbons having two or more carbon
atoms. In this way, the gaseous stream obtained in step (f) is
provided with a composition and/or heating value required for used
as a sales gas. For instance, the C2+ lean gaseous stream removed
from the top of the second gas/liquid separator in step (f) may
comprise < (less than) 10 mole % hydrocarbons having 2 of more
carbon atoms, preferably <5 mole %, more preferably <2 mole %
and even more preferably <1 mole %.
[0042] According to an embodiment described herein the gaseous
stream obtained in step (f) is sent to a gas network and not
liquefied to obtain a methane-rich LNG stream.
[0043] Further it may be that the gaseous stream obtained in step
(f) is heat exchanged against the feed stream.
[0044] Moreover, the LNG stream as fed in step (e) may have been
previously heat exchanged against the feed stream.
[0045] In a step (g), a liquid stream is removed from the bottom of
the second gas/liquid separator. This liquid stream may be further
processed. Preferably, during such further processing, this liquid
stream is subjected to fractionation thereby obtaining two or more
products, including ethane.
[0046] It is preferred that > (more than) 75 mole % of
hydrocarbons having 2 or more carbon atoms present in the partially
condensed feed stream are recovered in the liquid stream obtained
from the second gas/liquid separator, preferably >80, more
preferably >85, even more preferably >90, most preferably
>95 mole %. Viewed another way, it is preferred that .ltoreq.
(less than or equal to) 25 mole % of the hydrocarbons having 2 or
more carbon atoms present in the partially condensed feed stream
are transferred to the gaseous stream obtained in step (f),
preferably .ltoreq.20, more preferably .ltoreq.15, even more
preferably .ltoreq.10, most preferably .ltoreq.5 mole %.
[0047] For instance, it is preferred that > (more than) 75 mole
% of the ethane present in the paritially condensed feed stream is
recovered in the liquid stream obtained in step (g), preferably
>80, more preferably >85, even more preferably >90, most
preferably >95 mole %. Viewed another way, it is preferred that
s (less than or equal to) 25 mole % of the ethane present in the
partially condensed feed stream is transferred to the gaseous
stream obtained from the second gas/liquid separator in step (f),
preferably .ltoreq.20, more preferably .ltoreq.15, even more
preferably .ltoreq.10, most preferably .ltoreq.5 mole %. According
to an embodiment described herein the pressure drop during
expanding--in a step (d)--of the gaseous stream obtained from the
first gas/liquid separator is less than 15 bar, more preferably
less than 10 bar, even more preferably less than 5 bar. Herewith
the energy consumption in the treating process can be reduced.
[0048] Also it is preferred that the pressure in the second
gas/liquid separator is from 15 to 40 bar, preferably from 20 to 30
bar. Examples include from 23 to 27 bar and about 25 bar.
[0049] FIG. 1 schematically shows a process scheme (generally
indicated with reference no. 1) for the treating of a hydrocarbon
feed stream such as natural gas whereby ethane and heavier
hydrocarbons are recovered to a certain extent.
[0050] The process scheme of FIG. 1 comprises a first gas/liquid
separator 2, a second gas/liquid separator 3, a first expander 6, a
second expander 7 (in the from of a throttling valve), a separate
source 4 of LNG from a separate plant (in the embodiment of FIG. 1
an LNG storage tank at an LNG import terminal), a gas network 11
and a fractionation unit 9. The second gas/liquid separator 3 may
be provided in the form of a distillation column 3, such as a
de-methanizer as is the case in the embodiment of present FIG. 1.
The person skilled in the art will readily understand that further
elements may be present if desired.
[0051] During use, a partly condensed feed stream 10 containing
natural gas is supplied to the inlet 21 of the first gas/liquid
separator 2 at a certain inlet pressure and inlet temperature.
Typically, the inlet pressure to the first gas/liquid separator 2
will be between 10 and 100 bar, preferably above 30 bar and
preferably below 90 bar, more preferably below 70 bar. The
temperature will usually be between 0 and -80.degree. C. To obtain
the partly condensed feed stream 10, it may have been pre-cooled in
several ways. In the embodiment of FIG. 1, the feed steam has been
heat exchanged in heat exchanger 12 against a C2+ lean gaseous
stream 60 (hereinafter also referred to as gaseous overhead stream
60 or just overhead stream 60, and to be discussed hereafter) and
subsequently in heat exchanger 5 against a LNG stream, in the
embodiment of FIG. 1 an LNG stream 70 (indicated as streams 70a and
70b) originating from the separate plant. Instead of or in addition
to heat exchange against streams 60 and 70 also a common external
refrigerant such as propane or another cooler such as an air or
water cooler may be used to cool the feed stream 10.
[0052] If desired the feed stream 10 may have been further
pre-treated before it is fed to the first gas/liquid separator 2.
As an example, H.sub.2O, CO.sub.2, H.sub.2S and hydrocarbon
components having the molecular weight of pentane or higher may
also at least partially have been removed from the feed stream 10
before entering the first separator 2.
[0053] In the first gas/liquid separator 2, the feed stream 10 (fed
at inlet 21) is separated into a gaseous stream 20 (removed at
first outlet 22) and a liquid stream 30 (removed at second outlet
23). The gaseous stream 20, which may hereinafter be referred to as
the gaseous overhead stream 20, is enriched in methane relative to
the feed stream 10.
[0054] The liquid stream 30, which may hereinafter be referred to
as the liquid bottom stream 30, is generally liquid and usually
contains some components that are freezable when they would be
brought to a temperature at which methane is liquefied. The bottom
stream 30 may also contain hydrocarbons that can be separately
processed to form liquefied petroleum gas (LPG) products. The
stream 30 is expanded in the second expander 7 to the operating
pressure of the distillation column 3 (usually about 25 bar) and
fed into the same at a first feeding point 31 as stream 40. If
desired a further heat exchanger (not shown) may be present on line
40 to heat the stream 40. The second expander 7 may be any
expansion device such as a liquid expander as well as a flash
valve.
[0055] The gaseous overhead stream 20 removed at the first outlet
22 of the first separator 2 is at least partially condensed in the
first expander 6 and subsequently fed as an at least partially
condensed stream 50 into the distillation column 3 at a second
feeding point 32. The second feeding point 32 is at a higher level
than the first feeding point 31. If desired a further heat
exchanging step may take place between the first expander 6 and the
second feeding point 32. The pressure drop over the expander 6 may
be lower than 15 bar, even lower than 10 bar, as no extra cooling
is required for the stream 50 in view of the use of the cold stream
70 (to be discussed hereafter).
[0056] If desired (and as indicated with dashed lines in FIG. 1)
the gaseous overhead stream 20 may be split into two streams; the
`additional` stream 20a may be expanded in expander 6a and fed into
the distillation column at a further feeding point 37.
[0057] The LNG stream 70 is, after cooling the feed stream 10 in
heat exchanger 5, fed as stream 70b into the distillation column 3
at a third feeding point 33, the third feeding point 33 being at a
higher level than the second feeding point 32. Preferably the third
feeding point 33 is at or near the top of the distillation column
3.
[0058] Preferably, the pressure in the distillation column 3 is
from 15 to 40 bar, preferably from 20 to 30 bar.
[0059] Preferably, the temperature of the LNG stream 70 is below
-150.degree. C. just before heat exchanging (as stream 70a) against
stream 10 in heat exchanger 5, and below -100.degree. C. but
usually above -150.degree. C. just before feeding (as stream 70b)
in the second gas/liquid separator 3 at the third feeding point 33.
Herewith no reflux of the overhead stream 60 to the distillation
column 3 is required in order to recover a major part of the ethane
present in the feed stream 10 in the bottom product stream 80. As a
result the capital expenses are significantly reduced.
[0060] The gaseous overhead stream 60 obtained at the top of the
second gas/liquid separator 3 (at first outlet 34) is sent to the
gas network 11 (for use as a sales gas) after heat exchanging
against the feed stream 10 in heat exchanger 12 and optionally
compressing in compressor 8 (which may be functionally coupled to
first expander 6). Preferably, the gaseous stream 60 is not
subsequently liquefied.
[0061] A liquid stream 80, hereinafter also referred to as a liquid
bottom stream 80, is removed from the second outlet 35 of the
distillation column 3. Liquid bottom stream 80 may be cooled in
ambient cooler 81 and is usually subjected to one or more
fractionation steps, e.g. in a fractionation unit 9, to collect
various natural gas liquid products. For example, as shown in FIG.
1, fractionation unit 9 may produce at least two liquid streams
(100, 110), such as a liquefied petroleum gas (LPG) stream and a
condensate stream. Usually an ethane stream (not shown) is also
produced from fractionation unit 9.
[0062] If desired, and as shown in FIG. 1, a part of the liquid
bottom stream 80 may be returned to the bottom of the distillation
column 3 as stream 90, the remainder of stream 80 being indicated
with stream 80a.
[0063] The person skilled in the art will understand that the
amount of ethane recovered in the bottom stream will also be
dependent on the composition of the LNG stream 70 originating from
the source 4. In case the LNG stream 70 contains large amounts of
ethane, this ethane will be substantially recovered in the bottom
stream 80.
[0064] Table I gives an overview of the pressures and temperatures
of a stream at various parts in an example process of FIG. 1. The
feed stream in line 10 of FIG. 1 comprised approximately the
following composition: 79 mole % methane, 10 mole % ethane, 6 mole
% propane, 3 mole % butanes and pentane, and 2 mole % N.sub.2.
Other components such as H.sub.2S and H.sub.2O were previously
removed.
TABLE-US-00001 TABLE I Temperature Mole % Line Pressure (bar)
(.degree. C.) ethane 10 35.5 -70.0 10.0 20 35.4 -69.6 3.4 30 35.4
-69.6 20.8 40 20.2 -83.7 20.8 50 20.2 -91.6 3.4 60 20.0 -104.7 0.4
70a 20.0 -155 8.5 80 20.2 -19.0 51.4
[0065] It was found that according to the present invention the
amount of overhead gas stream 60 (that can be used as sales gas)
was relatively high when compared with the same line-up as FIG. 1,
but wherein a reflux column was used for the overhead stream 60 as
a result of which a part of the stream 60 was refluxed to the
distillation column 3.
[0066] The person skilled in the art will readily understand that
many modifications may be made without departing from the scope of
the invention. As an example, the compressor may comprise two or
more compression stages. Further, each heat exchanger may comprise
a train of heat exchangers.
* * * * *