U.S. patent application number 16/499652 was filed with the patent office on 2020-04-16 for overhead recycle process apparatus and method of overhead recycle processing of hydrocarbons.
This patent application is currently assigned to LINDE AKTIENGESELLSCHAFT. The applicant listed for this patent is LINDE AKTIENGESELLSCHAFT. Invention is credited to Heinz BAUER, Andreas BUB, Lisa KOPPL.
Application Number | 20200116427 16/499652 |
Document ID | / |
Family ID | 58544710 |
Filed Date | 2020-04-16 |
United States Patent
Application |
20200116427 |
Kind Code |
A1 |
BAUER; Heinz ; et
al. |
April 16, 2020 |
OVERHEAD RECYCLE PROCESS APPARATUS AND METHOD OF OVERHEAD RECYCLE
PROCESSING OF HYDROCARBONS
Abstract
An overhead recycle process apparatus (100) comprises a heat
exchange arrangement (116, 118, 120, 146, 150, 198) and a separator
(110) in fluid communication with an absorber (104) and a
de-ethaniser (106), the absorber (104) having a reflux inlet port
(164). An ethane rectifier (170) in fluid communication with the
de-ethaniser (106) is also provided, the de-ethaniser (106) being
arranged to provide cooling by heat exchange to an overhead stream
path (194) of the ethane rectifier (170). The ethane rectifier
(170) comprises a reflux drum (182) having an ethane outlet port
(184) and a vapour phase outlet port (185) in fluid communication
with the reflux inlet port (164) of the absorber (104).
Inventors: |
BAUER; Heinz; (Ebenhausen,
DE) ; KOPPL; Lisa; (Neuried, DE) ; BUB;
Andreas; (Munchen, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LINDE AKTIENGESELLSCHAFT |
Munich |
|
DE |
|
|
Assignee: |
LINDE AKTIENGESELLSCHAFT
Munich
DE
|
Family ID: |
58544710 |
Appl. No.: |
16/499652 |
Filed: |
March 22, 2018 |
PCT Filed: |
March 22, 2018 |
PCT NO: |
PCT/EP2018/057272 |
371 Date: |
September 30, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 2245/02 20130101;
F25J 3/0209 20130101; F25J 3/0233 20130101; F25J 3/0242 20130101;
F25J 2200/32 20130101; F25J 2200/74 20130101; F25J 2215/62
20130101; F25J 3/0238 20130101; F25J 2240/02 20130101; F25J 2200/04
20130101; F25J 2200/72 20130101; F25J 2205/04 20130101; F25J
2200/78 20130101 |
International
Class: |
F25J 3/02 20060101
F25J003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2017 |
EP |
17164141.8 |
Claims
1. An overhead recycle process apparatus (100) comprising: a heat
exchange arrangement (116, 118, 120, 146, 150, 198); a separator
(110) in fluid communication with an absorber (104) and a
de-ethaniser (106), the absorber (104) having a reflux inlet port
(164); and an ethane rectifier (170) in fluid communication with
the de-ethaniser (106), the de-ethaniser (106) being arranged to
provide cooling by heat exchange to an overhead stream path (194)
of the ethane rectifier (170); and the ethane rectifier (170)
comprises a reflux drum (182) having an ethane outlet port (184)
and a vapour outlet port (185) in fluid communication with the
reflux inlet port (164) of the absorber (104).
2. An apparatus as claimed in claim 1, wherein the de-ethaniser
(106) comprises a bottom product outlet port (197) arranged to
provide hydrocarbon fractions having a molecular weight heavier
than a molecular weight of ethane.
3. An apparatus as claimed in claim 1, further comprising: a side
stream circuit (172, 174, 176, 178, 180); wherein the de-ethaniser
(106) comprises a side stream inlet port (172) and a side stream
outlet port (174), the side stream outlet port (174) being disposed
above the side stream inlet port (172) of the de-ethaniser (106);
the ethane rectifier (170) comprises a rectifier bottom product
inlet port (176), a rectifier bottom product outlet port (178) and
a bottom product reservoir (180); the side stream circuit (172,
174, 176, 178, 180) extends from the side stream outlet port (174)
into the bottom product reservoir (180) via the rectifier bottom
product inlet port (176) and returns to the side stream inlet port
(172) via the rectifier bottom product outlet port (178); and the
side stream outlet port (174) is located at a location along the
de-ethaniser (170) corresponding to an expected presence of
elevated levels of ethane content in the de-ethaniser (106).
4. An apparatus as claimed in claim 1, wherein the reflux drum
(182) of the ethane rectifier (170) comprises a reflux inlet port
(186) and a rectification portion (190) of the ethane rectifier
(170) comprises an overhead stream outlet port (192), the overhead
stream path (194) extending from the overhead stream outlet port
(192) to the reflux inlet port (186) via the heat exchange
arrangement (120) so as to define an ethane reflux path.
5. An apparatus as claimed in claim 4, wherein the de-ethaniser
(106) comprises a primary reflux inlet port (154), a secondary
reflux inlet port (161) and an overhead stream outlet port (156); a
primary de-ethaniser reflux path (158) extends from the overhead
stream outlet port (156) of the de-ethaniser (106) to the primary
reflux inlet port (154) of the de-ethaniser (106) via the heat
exchange arrangement (118) and the separator (110); a secondary
de-ethaniser reflux path (159) branching from the primary
de-ethaniser reflux path (158) and extending to the secondary
reflux inlet port (161) via the heat exchange arrangement (120);
and the heat exchange arrangement (120) comprises an ethane reflux
heat exchanger (120), the secondary de-ethaniser reflux path (159)
and the ethane reflux path passing through the ethane reflux heat
exchanger (120).
6. An apparatus as claimed in claim 1, further comprising: a lean
gas outlet path (142); a lean gas outlet port (144) in fluid
communication with the lean gas outlet path (142); wherein the heat
exchange arrangement (116, 118, 120, 146, 150, 198) comprises a
first heat exchanger (116) and a second heat exchanger (118); and a
compressor (112); wherein the lean gas outlet path (142) extends
from an overhead stream outlet port (140) of the absorber to the
lean gas outlet port (144), passing through the second heat
exchanger (118) and the first heat exchanger (116); and the
compressor (112) is in the lean gas outlet path (142) after the
first heat exchanger (116).
7. An apparatus as claimed in claim 6, further comprising: a gas
feed inlet port (102); another separator (108) having an inlet port
in fluid communication with the gas feed inlet port (102) via the
first heat exchanger (116), the another separator (108) having a
vapour outlet port and a liquid outlet port.
8. An apparatus as claimed in claim 7, further comprising: an
expander (114) operably coupled to the compressor (112); wherein
the vapour outlet port of the another separator (108) is in fluid
communication with the expander (114) and the expander (114) is in
fluid communication with a bottom product reservoir of the absorber
(104); and the liquid outlet port of the another separator (108) is
in fluid communication with a first feed inlet port (126) of the
de-ethaniser (106).
9. An apparatus as claimed in claim 6, further comprising: a second
feed fluid path (130) in fluid communication at one end thereof
with a bottom fraction outlet port (132) of the absorber (104) and
in fluid communication at another end thereof with a second feed
inlet port (134) of the de-ethaniser (106); wherein the second feed
fluid path (130) passes through the first heat exchanger (116).
10. An apparatus as claimed in claim 6, wherein the separator (110)
comprises a vapour outlet port and a liquid outlet port, the vapour
outlet port being in fluid communication with the reflux inlet port
(164) of the absorber (104) via the second heat exchanger (118) and
the liquid outlet port being in fluid communication with the
primary reflux inlet port (154) of the de-ethaniser (106).
11. An apparatus as claimed in claim 10, wherein the overhead
outlet stream port (156) of the de-ethaniser (106) is in fluid
communication with an inlet port of the separator (110) via the
second heat exchanger (118).
12. An apparatus as claimed in claim 1, wherein the de-ethaniser
(106) comprises a bottom fraction reservoir (195), and a bottom
fraction inlet port (196) and a bottom fraction outlet port (197)
in fluid communication with the bottom fraction reservoir (195);
and a reboiler circuit path extends from the bottom fraction outlet
port (197) and returns to the bottom fraction reservoir (195) via
the bottom fraction inlet port (196), the reboiler circuit path
passing through the heat exchange arrangement (198).
13. An apparatus as claimed in claim 1, wherein the de-ethaniser
(106) comprises a heavy hydrocarbon fractions outlet port (199) for
hydrocarbon fractions having a molecular weight heavier than the
molecular weight of ethane.
14. An apparatus as claimed in claim 6, further comprising: a light
fractions compression and cooling arrangement (112, 146, 148, 150)
in fluid communication at a first end thereof with the lean gas
outlet port (144) and at a second end thereof with the first heat
exchanger (116); wherein the compression and cooling arrangement
(112, 146, 148, 150) comprises the compressor (112).
15. A method of overhead recycle processing of hydrocarbons, the
method comprising: drawing off (240) ethane from a de-ethaniser
(106); rectifying the drawn off ethane in a rectifier (170);
generating reflux (242) from an overhead stream path of the
rectifier (170); and introducing the reflux into a reflux drum
(182) of the rectifier (170).
Description
[0001] The present invention relates to an overhead recycle process
apparatus of the type that, for example, recovers hydrocarbon
products having a molecular weight heavier than ethane from natural
gas. The present invention also relates to a method of overhead
recycle processing of hydrocarbons, the method being of the type
that recovers hydrocarbon products having a molecular weight
heavier than ethane from natural gas.
[0002] In the field of hydrocarbon recovery from natural gas,
processes for the recovery hydrocarbons having molecular weights
heavier than ethane, for example natural gas liquids, are known.
One known process is the so-called overhead recycle process that
essentially draws a vapour stream from a de-ethaniser for
condensation and then introduction into an absorber as reflux in
order to rectify vapour leaving an expander. Heavier hydrocarbon
fractions are thereby absorbed in the absorber for recovery from a
bottom product reservoir of the de-ethaniser. The process is
described in U.S. Pat. No. 4,617,039, and is optimised for bulk
propane recovery.
[0003] It is often the case that recovery of considerable
quantities of ethane from the natural gas, for example 90% or more,
when recovering the heavier hydrocarbon fractions is not
commercially justified, because a demand for large quantities of
ethane is lacking. Nevertheless, a demand exists, for example in
the refrigerant market, to justify recovering a smaller quantity of
ethane, for example less than about 10%, such as less than 5%.
[0004] Known process architectures for the recovery of smaller
quantities of ethane from the natural gas employ, for example, a
sequence of fractionating units, for example a de-methaniser and a
de-ethaniser. However, such configurations are not cost-effective
for recovering relatively small quantities of ethane from the
natural gas where the primary consideration is the recovery of the
molecularly heavier hydrocarbon fractions. Additionally, if applied
in the context of the overhead recycle process described above,
efficiency of extraction of propane would be reduced.
[0005] According to a first aspect of the present invention, there
is provided an overhead recycle process apparatus comprising: a
heat exchange arrangement; a separator in fluid communication with
an absorber and a de-ethaniser, the absorber having a reflux inlet
port; and an ethane rectifier in fluid communication with the
de-ethaniser, the de-ethaniser being arranged to provide cooling by
heat exchange to an overhead stream path of the ethane rectifier;
and the ethane rectifier comprises a reflux drum having an ethane
outlet port and a vapour outlet port in fluid communication with
the reflux inlet port of the absorber.
[0006] The de-ethaniser may comprise a bottom product outlet port
arranged to provide hydrocarbon fractions having a molecular weight
heavier than a molecular weight of ethane.
[0007] The apparatus may further comprise: a side stream circuit;
wherein the de-ethaniser may comprise a side stream inlet port and
a side stream outlet port; the side stream outlet port may be
disposed above the side stream inlet port of the de-ethaniser; the
ethane rectifier may comprise a rectifier bottom product inlet
port, a rectifier bottom product outlet port and a bottom product
reservoir; the side stream circuit may extend from the side stream
outlet port into the bottom product reservoir via the rectifier
bottom product inlet port and returns to the side stream inlet port
via the rectifier bottom product outlet port; and the side stream
outlet port may be located at a location along the de-ethaniser
corresponding to an expected presence of elevated levels of ethane
content in the de-ethaniser.
[0008] The reflux drum of the ethane rectifier may comprise a
reflux inlet port and a rectification portion of the ethane
rectifier may comprise an overhead stream outlet port; the overhead
stream path may extend from the overhead stream outlet port to the
reflux inlet port via the heat exchange arrangement so as to define
an ethane reflux path.
[0009] The de-ethaniser may comprise a primary reflux inlet port, a
secondary reflux inlet port and an overhead stream outlet port; a
primary de-ethaniser reflux path may extend from the overhead
stream outlet port of the de-ethaniser to the primary reflux inlet
port of the de-ethaniser via the heat exchange arrangement and the
separator; a secondary de-ethaniser reflux path may branch from the
primary de-ethaniser reflux path and extend to the secondary reflux
inlet port via the heat exchange arrangement; and the heat exchange
arrangement may comprise an ethane reflux heat exchanger; the
secondary de-ethaniser reflux path and the ethane reflux path may
pass through the ethane reflux heat exchanger.
[0010] The apparatus may further comprise: a lean gas outlet path;
a lean gas outlet port in fluid communication with the lean gas
outlet path; wherein the heat exchange arrangement may comprise a
first heat exchanger and a second heat exchanger; and a compressor;
wherein the lean gas outlet path may extend from an overhead stream
outlet port of the absorber to the lean gas outlet port, and pass
through the second heat exchanger and the first heat exchanger; and
the compressor may be in the lean gas outlet path after the first
heat exchanger.
[0011] The apparatus may further comprise: a gas feed inlet port;
another separator that may have an inlet port in fluid
communication with the gas feed inlet port via the first heat
exchanger; the another separator may have a vapour outlet port and
a liquid outlet port.
[0012] The apparatus may further comprise: an expander operably
coupled to the compressor; wherein the vapour outlet port of the
another separator may be in fluid communication with the expander
and the expander may be in fluid communication with a bottom
product reservoir of the absorber; and the liquid outlet port of
the another separator may be in fluid communication with a first
feed inlet port of the de-ethaniser.
[0013] The apparatus may further comprise: a second feed fluid path
in fluid communication at one end thereof with a bottom fraction
outlet port of the absorber and in fluid communication at another
end thereof with a second feed inlet port of the de-ethaniser;
wherein the second feed fluid path may pass through the first heat
exchanger.
[0014] The separator may comprise a vapour outlet port and a liquid
outlet port; the vapour outlet port may be in fluid communication
with the reflux inlet port of the absorber via the second heat
exchanger and the liquid outlet port may be in fluid communication
with the primary reflux inlet port of the de-ethaniser.
[0015] The overhead outlet stream port of the de-ethaniser may be
in fluid communication with an inlet port of the separator via the
second heat exchanger.
[0016] The de-ethaniser may comprise: a bottom fraction reservoir,
and a bottom fraction inlet port and a bottom fraction outlet port
in fluid communication with the bottom fraction reservoir; and a
reboiler circuit path may extend from the bottom fraction outlet
port and return to the bottom fraction reservoir via the bottom
fraction inlet port; the reboiler circuit path may pass through the
heat exchange arrangement.
[0017] The de-ethaniser may comprise a heavy hydrocarbon fractions
outlet port for hydrocarbon fractions having a molecular weight
heavier than the molecular weight of ethane.
[0018] The apparatus may further comprise: a light fractions
compression and cooling arrangement in fluid communication at a
first end thereof with the lean gas outlet port and at a second end
thereof with the first heat exchanger; wherein the compression and
cooling arrangement may comprise the compressor.
[0019] The lean gas outlet port may be associated with hydrocarbon
fractions having a molecular weight lighter than the molecular
weight of ethane.
[0020] According to a second aspect of the present invention, there
is provided a method of overhead recycle processing of
hydrocarbons, the method comprising: drawing off ethane from a
de-ethaniser; rectifying the drawn off ethane in a rectifier;
generating reflux from an overhead stream path of the rectifier;
and introducing the reflux into a reflux drum of the rectifier.
[0021] The method may further comprise providing an ethane
rectifier having a reflux drum and an absorber; wherein an overhead
stream of the reflux drum provides reflux to the absorber.
[0022] It is thus possible to provide an overhead recycle process
apparatus and method capable of recovering relatively small
quantities of ethane whilst recovering molecularly heavier
hydrocarbon fractions from natural gas in an efficient and economic
manner. Furthermore, the ethane recovered is of a desired purity,
for example better than 95 mol %, such as better than 98 mol %.
Additionally, the apparatus and method obviates the need to provide
additional rotating hardware, for example compressors and pumps, in
order to support recovery of the ethane.
[0023] At least one embodiment of the invention will now be
described, by way of example only, with reference to the
accompanying drawings, in which:
[0024] FIG. 1 is a schematic diagram of an overhead recycle process
apparatus constituting an embodiment of the invention; and
[0025] FIGS. 2 to 4 are parts of a flow diagram of a method of
overhead recycle processing constituting another embodiment of the
invention.
[0026] Referring to FIG. 1, an overhead recycle process apparatus
100 comprises a natural gas inlet port 102, an absorber 104 and a
de-ethaniser 106 in fluid communication with each other via a heat
exchange arrangement, a first separator 108, a second separator
110, a first compressor 112, an expander 114 and other components
to be described later herein, for example Joule-Thomson devices,
such as throttling devices, and pumps.
[0027] In this example, the heat exchange arrangement comprises a
first heat exchanger 116, a second heat exchanger 118 and an ethane
reflux heat exchanger 120.
[0028] An inlet fluid path 122 extends from the natural gas inlet
port 102 and passes through the first heat exchanger 116 via first
inlet and outlet ports of the first heat exchanger 116 and is in
fluid communication with an inlet port of the first separator 108.
The first separator 108 has a first vapour outlet port and a first
liquid outlet port, the first vapour outlet port of the first
separator 108 being in fluid communication with a bottom product
inlet port 124 of the absorber 104 via the expander 114. The first
liquid outlet port of the first separator 108 is in fluid
communication with a first feed inlet port 126 of the de-ethaniser
106 via a first Joule-Thomson device, for example a first valve
128.
[0029] A second feed path 130 is in fluid communication at a first
end thereof with a bottom product outlet port 132 of the absorber
104 and at a second end thereof with a second feed inlet port 134.
A first pump 136 is disposed in the second feed path 130 before the
second feed path 130 passes through the first heat exchanger 116
via second inlet and outlet ports of the first heat exchanger 116.
A second Joule-Thomson device, such as a second valve 138, is
disposed in the second feed path 130 before the second end of the
second feed path 130 reaches the second feed inlet port 134, but
downstream of the first heat exchanger 116.
[0030] The absorber 104 has an overhead vapour outlet port 140 and
a lean gas outlet path 142 is in fluid communication with the
overhead vapour outlet port 140 at a first end thereof, a second
end of the lean gas outlet path 142 being in fluid communication
with a lean gas outlet port 144. From the overhead vapour outlet
port 140, the lean gas outlet path 142 passes through the second
heat exchanger 118 via first inlet and outlet ports of the second
heat exchanger 118 before passing subsequently through the first
heat exchanger 116 via third inlet and outlet ports thereof. The
lean gas outlet path 142 then passes through a light fractions
compression and cooling arrangement disposed between the first heat
exchanger 116 and the lean gas outlet port 144. In this example,
the light fractions compression and cooling arrangement comprises
the first compressor 112 having an inlet port in fluid
communication with the third outlet port of the first heat
exchanger 116, an outlet port of the first compressor 112 being in
fluid communication with an intermediary heat exchanger, for
example an intercooler 146. An outlet port of the intercooler 148
is in fluid communication with an inlet port of a second compressor
148, an outlet port of the second compressor 148 being in fluid
communication with a post-compression heat exchanger, for example a
post- or after-cooler 150. An outlet port of the after-cooler 150
is in fluid communication with the lean gas outlet port 144. In
this example, the first compressor 112 is operably coupled to the
expander 114 by a drive shaft 152.
[0031] The de-ethaniser 106 also comprises a de-ethaniser primary
reflux inlet port 154, and an overhead vapour outlet port 156 in
fluid communication with a primary de-ethaniser reflux path 158 at
a first end thereof, the primary de-ethaniser reflux path 158 being
in fluid communication with the de-ethaniser primary reflux inlet
port 154 at a second end thereof. The primary de-ethaniser reflux
path 158 extends from the overhead vapour outlet inlet port 156 to
an inlet port of the second separator 110, passing through the
second heat exchanger 118 via second inlet and outlet ports
thereof. The second separator 110 comprises a second vapour outlet
port and a second liquid outlet port, the second liquid outlet port
being in fluid communication with a second pump 160 and a third
Joule-Thomson device, for example a third valve 162, disposed
downstream of the second pump 160 before the primary de-ethaniser
reflux path 158 reaches the de-ethaniser primary reflux inlet port
154.
[0032] A secondary de-ethaniser reflux path 159 is in fluid
communication at a first end thereof with the primary de-ethaniser
reflux path 158 between the second pump 160 and the third valve
162. The secondary de-ethaniser reflux path 159 passes through the
ethane reflux heat exchanger 120 via first inlet and outlet ports
thereof. A second end of the secondary de-ethaniser reflux path 159
is in fluid communication with a de-ethaniser secondary reflux
inlet port 161.
[0033] The second vapour outlet port of the second separator 110 is
in fluid communication with an absorber reflux inlet port 164 of
the absorber 104 by way of an absorber reflux path 166 that is in
fluid communication with the second vapour outlet port of the
second separator 110 at a first end thereof. The absorber reflux
path 166 also passes through the second heat exchanger 118 via
third inlet and outlet ports of the second heat exchanger 118. A
fourth Joule-Thomson device, for example a fourth valve 168, is
disposed in the absorber reflux path 166 between the second heat
exchanger 118 and the absorber reflux inlet port 164.
[0034] An ethane rectifier 170 is in fluid communication with the
de-ethaniser 106 via a side stream circuit. In this regard, the
de-ethaniser comprises a side stream inlet port 172 and a side
stream outlet port 174, the side stream outlet port 174 being
disposed above the side stream inlet port 172. The ethane rectifier
170 comprises a rectifier bottom product inlet port 176, a
rectifier bottom product outlet port 178 and a bottom product
reservoir 180. The side stream circuit extends from the side stream
outlet port 174 into the bottom product reservoir 180 via the
rectifier bottom product inlet port 176 and returns to the side
stream inlet port 172, below the side stream outlet port 174, via
the rectifier bottom product outlet port 178. The side stream
outlet port 174 is located at a location along the de-ethaniser 106
corresponding to an expected presence of elevated levels of ethane
content in the de-ethaniser 106, and is located below the second
feed inlet port 134, although it should be appreciated that in some
embodiments the side stream outlet port 174 can be disposed
slightly above the second feed inlet port 134.
[0035] The ethane rectifier 170 comprises a reflux drum 182 having
an ethane outlet port 184, an overhead vapour outlet port 185 and a
reflux inlet port 186, the overhead vapour outlet port 185 being in
fluid communication with the absorber reflux inlet port 164 via a
fifth Joule-Thomson device, for example a fifth valve 188. A
rectification portion 190 of the ethane rectifier 170 comprises an
overhead stream outlet port 192 in fluid communication with a first
end of an overhead stream path 194, a second end of the overhead
stream path 194 being in fluid communication with the reflux inlet
port 186 via the ethane reflux heat exchanger 120.
[0036] The de-ethaniser 106 also comprises a bottom fractions
reservoir 195, and a bottom fractions inlet port 196 and a bottom
fractions outlet port 197 in fluid communication with the bottom
fractions reservoir 195. A reboiler circuit path extends from the
bottom fractions outlet port 197 and returns to the bottom
fractions reservoir 195 via the bottom fractions inlet port 196. In
this example, the reboiler circuit path passes through a reboiler
heat exchanger 198. The bottom fractions outlet port 197 is also in
fluid communication with a heavy hydrocarbon fractions outlet port
199 at a temperature of between about 110.degree. C. and about
130.degree. C., for example about 118.degree. C., and a pressure of
between about 2.5 MPa (25 bar abs) and about 4 MPa (40 bar abs),
for example about 3.4 MPa (34 bar abs).
[0037] In this example, the heat exchange arrangement also
comprises the intercooler 146, the after-cooler 150 and the
reboiler heat exchanger 198.
[0038] In operation (FIGS. 2 to 4), natural gas is supplied at the
natural gas inlet port 102. In this example, the gas is at a
temperature of between about 10.degree. C. and about 60.degree. C.,
for example about 40.degree. C., and a pressure of between about 4
MPa (40 bar abs) and about 8 MPa (80 bar abs), for example about 6
MPa (60 bar abs). The natural gas follows the inlet fluid path 122
and passes through the first heat exchanger 116, where the natural
gas is cooled and partially liquefied (Step 200) through heat
exchange, to yield a fluid between -55.degree. C. and about
-35.degree. C. in temperature, for example about -44.degree. C.,
and between about 3.9 MPa (39 bar abs) and about 7.9 MPa (79 bar
abs) in pressure, for example 5.9 MPa (59 bar abs). The cooled and
partially liquefied natural gas then enters the first separator 108
(Step 202), the vapour fraction being between about 0.94 mol/mol
and about 0.99 mol/mol, for example about 0.97 mol/mol, The liquid
fraction of the cooled natural gas leaves the first separator 108
and is cooled further by passage through the first valve 128 before
entering (Step 204) the de-ethaniser 106 at a temperature of
between about -65.degree. C. and about -45.degree. C., for example
about -56.degree. C., and a pressure of between about 2.5 MPa (25
bar abs) and about 4 MPa (40 bar abs), for example about 3.4 MPa
(34 bar abs). The vapour fraction of the cooled liquid fraction is
between about 0.15 mol/mol and about 0.3 mol/mol, for example about
0.23 mol/mol.
[0039] The vapour fraction of the cooled natural gas enters the
expander 114 where the vapour fraction undergoes expansion (Step
206) leading to a drop in pressure and temperature of the vapour
fraction. The expanded vapour, which is now partially condensed, is
then fed (Step 208) into a bottom product reservoir of the absorber
104. In this example, the expanded vapour is at a temperature of
between about -80.degree. C. and about -60.degree. C., for example
about -71.degree. C., and a pressure of between about 2.5 MPa (25
bar abs) and about 4 MPa (40 bar abs), for example about 3.2 MPa
(32 bar abs). The vapour fraction of the expanded vapour is between
about 0.9 mol/mol and about 0.98 mol/mol, for example about 0.96
mol/mol.
[0040] In the absorber 104, vapour fractions leaving the absorber
104 via the overhead vapour outlet port 140 do so at a temperature
of between about -85.degree. C. and about -65.degree. C., for
example about -75.degree. C., and a pressure of between about 2.5
MPa (25 bar abs) and about 4 MPa (40 bar abs), for example about
3.2 MPa (32 bar abs), and follow the lean gas outlet path 142 and
pass through the second heat exchanger 118 and then the first heat
exchanger 116. Thereafter, the light fractions compression and
cooling arrangement comprising the first and second compressors
112, 148 and the intercooler 146 and the post-cooler 150 compress
and cool (Step 210) the so-called "light" fractions present in the
lean gas outlet path 142, for example nitrogen, methane and ethane.
The light fractions have a lower molecular weight than propane and
are present at the lean gas outlet port 144, and are at a
temperature of between about 10.degree. C. and about 60.degree. C.,
for example about 37.degree. C., and a pressure of between about 4
MPa (40 bar abs) and about 10 MPa (100 bar abs), for example about
6 MPa (60 bar abs). In this example, the lean gas outlet path 142
supports cooling in the first and second heat exchangers 116,
118.
[0041] Liquid fractions at the bottom of the absorber 104 leave the
absorber 104 at a temperature of between about -80.degree. C. and
about -65.degree. C., for example about -72.degree. C., and a
pressure of between about 2.5 MPa (25 bar abs) and about 4 MPa (40
bar abs), for example about 3.2 MPa (32 bar abs), and are pumped by
the first pump 136 so as to follow the second feed fluid path 130,
the liquid fractions passing through the first heat exchanger 116,
thereby experiencing heating and partial vaporisation. Thereafter,
the warmed liquid fractions pass through the second valve 138,
resulting in the cooling of the liquid fractions in the second feed
fluid path 130, and then enter the de-ethaniser 106 via the second
feed inlet port 134 (Step 212) at a temperature of between about
-10.degree. C. and about 30.degree. C., for example about
10.degree. C., and a pressure of between about 2.5 MPa (25 bar abs)
and about 4 MPa (40 bar abs), for example about 3.4 MPa (34 bar
abs). The vapour fraction of the fluid entering the de-ethaniser
106 is between about 0.7 mol/mol and about 1.0 mol/mol, for example
about 0.82 mol/mol.
[0042] An overhead vapour stream emanates from the overhead vapour
port 156 of the de-ethaniser 106 at a temperature of between about
-15.degree. C. and about 10.degree. C., for example about
-2.degree. C., and a pressure of between about 2.5 MPa (25 bar abs)
and about 4 MPa (40 bar abs), for example about 3.4 MPa (34 bar
abs), and follows the primary de-ethaniser reflux path 158 and
enters the second separator 110 (Step 220) at a temperature of
between about -25.degree. C. and about 0.degree. C., for example
about -16.degree. C., and a pressure of between about 2.5 MPa (25
bar abs) and about 4 MPa (40 bar abs), for example about 3.3 MPa
(33 bar abs). The vapour fraction of the fluid entering the second
separator 110 is between about 0.75 mol/mol and about 0.95 mol/mol,
for example about 0.86 mol/mol. Vapour fractions leave the second
separator 110 and follow the absorber reflux path 166 and pass
through the second heat exchanger 118 and the fourth valve 168
where the vapour fractions are cooled (Step 222) before entering
the absorber 104 via the absorber reflux inlet port 164 at a
temperature of between about -80.degree. C. and about -65.degree.
C., for example about -72.degree. C., and a pressure of between
about 2.5 MPa (25 bar abs) and about 4 MPa (40 bar abs), for
example about 3.2 MPa (32 bar abs). The vapour fraction of the
fluid entering the absorber 104 via the absorber reflux inlet port
164 is between about 0.2 mol/mol and about 0.35 mol/mol, for
example about 0.27 mol/mol.
[0043] Liquid fractions leave the second separator 110 and are
pumped (Step 226) by the second pump 160 to the de-ethaniser
primary reflux inlet port 154 via the third valve 162, which serves
to cool the liquid fractions passing therethrough. The cooled
liquid fractions then enter the de-ethaniser primary reflux inlet
port 154 at a temperature of between about -25.degree. C. and about
0.degree. C., for example about -15.degree. C., and a pressure of
between about 2.5 MPa (25 bar abs) and about 4 MPa (40 bar abs),
for example about 3.4 MPa (34 bar abs) and serve as reflux (Step
228). A portion of the liquid fractions is tapped off the primary
de-ethaniser reflux path 158 so as to follow the secondary
de-ethaniser reflux path 159, the tapped off liquid fractions pass
(Step 230) through the ethane reflux heat exchanger 120 to support
cooling by the ethane reflux heat exchanger 120, before entering
(Step 232) the de-ethaniser 106 via the secondary reflux inlet port
161 a temperature of between about 0.degree. C. and about
20.degree. C., for example about 12.degree. C., and a pressure of
between about 2.5 MPa (25 bar abs) and about 4 MPa (40 bar abs),
for example about 3.3 MPa (33 bar abs). The vapour fraction of the
fluid entering the de-ethaniser 106 via the secondary reflux inlet
port 161 is between about 0.1 mol/mol and about 0.35 mol/mol, for
example about 0.26 mol/mol. When tapped off, the tapped off liquid
fractions mentioned above are at a temperature of between about
-25.degree. C. and about 0.degree. C., for example about
-15.degree. C., and a pressure of between about 2.5 MPa (25 bar
abs) and about 4 MPa (40 bar abs), for example about 3.8 MPa (38
bar abs). The flow fraction of the secondary de-ethaniser reflux
path 159 is between about 60% and about 100%, for example about
90%, of the total liquid leaving the separator 110 in the primary
de-ethaniser reflux path 158.
[0044] A proportion of the bottom fractions leaving the
de-ethaniser 106 via the bottom fraction outlet port 197 follow a
reboiler circuit path (Step 234) and are heated and partially
vaporised in the reboiler heat exchanger 198 and reintroduced into
the bottom fraction reservoir 195 of the de-ethaniser 106. The
remaining proportion of the bottom fractions leaving the
de-ethaniser 106 via the bottom fraction outlet port 197 are drawn
off (Step 236) via the heavy hydrocarbon fractions outlet port
199.
[0045] Ethane present in the de-ethaniser 106 is circulated (Step
240) through a side stream circuit; the ethane vapour leaves the
de-ethaniser 106 via the side stream outlet port 174 at a
temperature of between about 60.degree. C. and about 80.degree. C.,
for example about 70.degree. C., and a pressure of between about
2.5 MPa (25 bar abs) and about 4 MPa (40 bar abs), for example
about 3.4 MPa (34 bar abs), and enters the bottom product reservoir
180 of the ethane rectifier 170. Lighter fractions in vapour phase
rise through the ethane rectifier 170, whilst heavier liquid
fractions reside in the bottom product reservoir 180, and are
returned to the de-ethaniser via the rectifier bottom product
outlet port 178 and the side stream inlet port 172 at a temperature
of between about 50.degree. C. and about 70.degree. C., for example
about 60.degree. C., and a pressure of between about 2.5 MPa (25
bar abs) and about 4 MPa (40 bar abs), for example about 3.4 MPa
(34 bar abs). The vapour fractions travelling up the rectification
portion 190 of the ethane rectifier 170 encounter reflux
originating from the reflux drum 182, which serves to rectify the
vapour fractions before the vapour fractions leave the
rectification portion 190 of the ethane rectifier 170 via the
overhead stream outlet port 192 at a temperature of between about
5.degree. C. and about 25.degree. C., for example about 14.degree.
C., and a pressure of between about 2.5 MPa (25 bar abs) and about
4 MPa (40 bar abs), for example about 3.4 MPa (34 bar abs). The
vapour fractions then follow the overhead stream path 194 and pass
through the ethane reflux heat exchanger 120 in which they are
cooled and at least partially condensed (Step 242), before entering
the reflux drum 182 via the reflux inlet port 186 at a temperature
of between about 0.degree. C. and about 20.degree. C., for example
about 11.degree. C., and a pressure of between about 2.5 MPa (25
bar abs) and about 4 MPa (40 bar abs), for example about 3.4 MPa
(34 bar abs) to provide the reflux mentioned above. The reflux
comprises between about 0 mol/mol and about 0.1 mol/mol vapour, for
example about 0 mol/mol vapour. The reflux travels down the
rectification portion 190 of the ethane rectifier 170, and a
proportion of the ethane in the reflux drum 182 is drawn (Step 244)
from the reflux drum 182 at the ethane outlet port 184 at a
temperature of between about 0.degree. C. and about 20.degree. C.,
for example about 11.degree. C., and a pressure of between about
2.5 MPa (25 bar abs) and about 4 MPa (40 bar abs), for example
about 3.4 MPa (34 bar abs).
[0046] An overhead drum stream leaving the reflux drum 182 via the
overhead vapour outlet port 185 undergoes cooling by passage
through the fifth valve 188, before being fed into the absorber
reflux path 166 where the cooled overhead drum stream contributes
(Step 246) to the reflux entering the absorber 104 via the absorber
reflux inlet port 164.
[0047] The skilled person should appreciate that the
above-described implementations are merely examples of the various
implementations that are conceivable within the scope of the
appended claims. Indeed, although in this example, a heat exchanger
arrangement comprises the various heat exchangers, the skilled
person will appreciate that cooling can be provided using any
suitable manner of cooling and distribution of cooling
apparatus.
[0048] Although the above examples have been described in the
context of gases, the skilled person should appreciate that fluids
can be employed.
* * * * *