U.S. patent application number 15/658650 was filed with the patent office on 2017-11-23 for integrated process for ngl (natural gas liquids recovery) and lng (liquefaction of natural gas).
This patent application is currently assigned to LINDE ENGINEERING NORTH AMERICA INC.. The applicant listed for this patent is LINDE ENGINEERING NORTH AMERICA INC.. Invention is credited to Heinz BAUER, Stephan BURMBERGER, Danielle R. GOLDBECK, Christoph HERTEL, Ronald D. KEY, Aleisha MARTY.
Application Number | 20170336138 15/658650 |
Document ID | / |
Family ID | 51015634 |
Filed Date | 2017-11-23 |
United States Patent
Application |
20170336138 |
Kind Code |
A1 |
BURMBERGER; Stephan ; et
al. |
November 23, 2017 |
INTEGRATED PROCESS FOR NGL (NATURAL GAS LIQUIDS RECOVERY) AND LNG
(LIQUEFACTION OF NATURAL GAS)
Abstract
The invention relates to an integrated process and apparatus for
liquefaction of natural gas and recovery of natural gas liquids. In
particular, the improved process and apparatus reduces the energy
consumption of a Liquefied Natural Gas (LNG) unit by using a
portion of the already cooled overhead vapor from a fractionation
column from an NGL (natural gas liquefaction) unit to, depending
upon composition, provide, for example, reflux for fractionation in
the NGL unit and/or a cold feed for the LNG unit, or by cooling,
within the NGL unit, a residue gas originating from a fractionation
column of the NGL unit and using the resultant cooled residue gas
to, depending upon composition, provide, for example, reflux/feed
for fractionation in the NGL and/or a cold feed for the LNG unit,
thereby reducing the energy consumption of the LNG unit and
rendering the process more energy-efficient.
Inventors: |
BURMBERGER; Stephan;
(Neuried, DE) ; GOLDBECK; Danielle R.; (Tulsa,
OK) ; HERTEL; Christoph; (Wolfratshausen, DE)
; MARTY; Aleisha; (Broken Arrow, OK) ; BAUER;
Heinz; (Ebenhausen, DE) ; KEY; Ronald D.;
(Broken Arrow, OK) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LINDE ENGINEERING NORTH AMERICA INC. |
BLUE BELL |
PA |
US |
|
|
Assignee: |
LINDE ENGINEERING NORTH AMERICA
INC.
BLUE BELL
PA
|
Family ID: |
51015634 |
Appl. No.: |
15/658650 |
Filed: |
July 25, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14143755 |
Dec 30, 2013 |
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15658650 |
|
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61746727 |
Dec 28, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 1/0045 20130101;
F25J 2240/02 20130101; F25J 1/0204 20130101; F25J 1/0205 20130101;
F25J 1/0208 20130101; F25J 2270/90 20130101; F25J 1/0052 20130101;
F25J 2200/78 20130101; F25J 1/004 20130101; F25J 3/0238 20130101;
F25J 1/023 20130101; F25J 2200/30 20130101; F25J 2200/74 20130101;
F25J 2200/76 20130101; F25J 2270/66 20130101; F25J 1/021 20130101;
F25J 2200/70 20130101; F25J 3/0233 20130101; F25J 1/005 20130101;
F25J 1/0072 20130101; F25J 2270/42 20130101; F25J 2290/40 20130101;
F25J 1/0212 20130101; F25J 1/0035 20130101; F25J 2220/62 20130101;
F25J 2205/04 20130101; F25J 2200/02 20130101; F25J 3/0209 20130101;
F25J 1/0241 20130101; F25J 2245/90 20130101; F25J 1/0022 20130101;
F25J 1/0215 20130101; F25J 2260/20 20130101; F25J 1/0219
20130101 |
International
Class: |
F25J 3/02 20060101
F25J003/02; F25J 1/02 20060101 F25J001/02; F25J 1/00 20060101
F25J001/00 |
Claims
1. A process for integrated liquefaction of natural gas and
recovery of natural gas liquids, said process comprising: cooling a
feed stream containing light hydrocarbons in one or more heat
exchangers, wherein said feed stream is cooled and partially
condensed by indirect heat exchange; introducing the partially
condensed feed stream into a gas/liquid cold separator producing an
overhead gaseous stream and bottoms liquid stream which are to be
introduced into a fractionation system, said fractionation system
comprising a demethanizer column; expanding at least a portion of
the overhead gaseous stream from the gas/liquid cold separator and
introducing the expanded portion of said overhead gaseous stream
into an upper region of said demethanizer column; introducing at
least a portion of the bottoms liquid stream from said gas/liquid
cold separator into said demethanizer column at an intermediate
point thereof; removing a liquid product stream from the bottom of
said demethanizer column; and removing a overhead gaseous stream
from the top of said demethanizer column, said process further
comprising: (A) removing a portion of the overhead gaseous stream
from the demethanizer column as a side stream, and partially
liquefying said side stream by heat exchange; introducing the
partially liquefied side stream into a further separation means,
recovering liquid product from said further separation means and
introducing the recovered liquid product into said demethanizer
column as a liquid reflux stream; and recovering an overhead vapor
stream from said further separation means, subjecting said overhead
vapor stream from said further separation means to indirect heat
exchange for additional cooling and partial condensation, and
removing the resultant condensate from said partial condensation as
liquefied natural gas product; or (B) subjecting at least a portion
of said overhead gaseous from the demethanizer column to heat
exchange wherein said overhead gaseous from the demethanizer column
is used to cool at least one other process stream, and then
compressing the least a portion of said overhead gaseous from the
demethanizer column from the heat exchange to form a residue gas;
cooling at least portion of said residue gas to obtain a cooled
residue gas; introducing a part of the cooled residue gas into said
demethanizer column as a reflux stream; and introducing another
part of the cooled residue gas into a further separation means, and
recovering liquefied natural gas product from said further
separation means.
2. (canceled)
3. (canceled)
4. (canceled)
5. The process according to claim 1, wherein: said feed stream
containing light hydrocarbons is split into at least a first
partial stream and a second partial stream; introducing said first
partial stream of the feed stream into a main heat exchanger
wherein said first partial stream of the feed stream is cooled and
partially condensed by indirect heat exchange with process streams
removed from said demethanizer column; introducing said second
partial stream of the feed stream into another heat exchanger
wherein said second partial stream of the feed stream is cooled and
partially condensed by indirect heat exchange at least a portion of
the overhead gaseous stream from said demethanizer column;
recombining said first and second partial streams of the feed
stream, and optionally subjecting the resultant recombined feed
stream to heat exchange with a refrigerant; and introducing the
recombined feed stream into said gas/liquid cold separator to
produce said overhead gaseous stream and said bottoms liquid
stream.
6-16. (canceled)
17. An apparatus for integration of liquefaction of natural gas and
recovery of natural gas liquids, said apparatus comprising: one or
more heat exchangers for cooling and partially condensing by
indirect heat exchange a feed stream containing light hydrocarbons;
a gas/liquid cold separator and means for introducing a partially
condensed feed stream from the one or more heat exchangers into the
gas/liquid cold separator, the gas/liquid cold separator having
upper outlet means for removing an overhead gaseous stream and
lower outlet means for removing a bottoms liquid stream; means for
introducing overhead gaseous stream and bottoms liquid stream from
the gas/liquid cold separator into a fractionation system
comprising a demethanizer column, the means comprising an expansion
device for expanding at least a portion of overhead gaseous stream
from the gas/liquid cold separator and means for introducing
expanded overhead gaseous stream into an upper region of a
demethanizer column, and means for introducing at least a portion
of bottoms liquid stream from the gas/liquid cold separator into a
demethanizer column at an intermediate point thereof; means for
removing a liquid product stream from the bottom of the
demethanizer column; means for removing a overhead gaseous stream
from the top of the demethanizer column, and said apparatus further
comprising: (A) (i) a heat exchanger for subjecting a first portion
of the overhead gaseous stream from the demethanizer column to
indirect heat exchange with a stream obtained by combining a
portion of the overhead gaseous stream from the gas/liquid cold
separator and a portion of the bottoms liquid stream from
gas/liquid cold separator to obtain a residue gas; (ii) means for
removing a second portion of the overhead gaseous from the
demethanizer column as a side stream, and a further heat exchanger
for partially liquefying the side stream by heat exchange; (iii)
means for introducing the partially liquefied side stream into a
further separation means, means for recovering liquid product from
the further separation means and introducing the recovered liquid
product into the demethanizer column as a liquid reflux stream, and
(iv) means for recovering an overhead vapor stream from the further
separation means, a further heat exchange means for subjecting this
overhead vapor stream to indirect heat exchange for additional
cooling and partial condensation, and means for removing the
resultant condensate as a final LNG liquid product; or (B) (i) a
heat exchanger for subjecting the demethanizer column overhead
gaseous stream to indirect heat exchange with a stream obtained by
combining a portion of the overhead gaseous stream from the
gas/liquid cold separator and a portion of the bottoms liquid
stream from gas/liquid cold separator; (ii) means for subjecting
the overhead gaseous stream from the demethanizer column to further
heating and a compressor for compressing the overhead gaseous
stream from the demethanizer column to produce a residue gas; (iii)
a further heat exchanger for cooling at least a portion of the
residue gas whereby the portion of the residue gas is partially
liquefied; (iv) means for introducing this partially liquefied
residue gas into a further separation means; (v) means for
recovering liquid product from the further separation means and
introducing the recovered liquid product as reflux to the
demethanizer column; (vi) means for recovering an overhead vapor
stream from the further separation means, means for subjecting this
overhead vapor stream to heat exchange whereby the overhead vapor
stream is partially liquefied; (vii) means for introducing this
partially liquefied overhead vapor stream into another further
separation means; and (viii) means for recovering LNG liquid
product from the another further separation means.
18. (canceled)
19. The process according to claim 1, wherein said process
comprises: removing a portion of the overhead gaseous from the
demethanizer column as a side stream, and partially liquefying said
side stream by heat exchange; introducing the partially liquefied
side stream into a further separation means, recovering liquid
product from said further separation means and introducing the
recovered liquid product into said demethanizer column as a liquid
reflux stream; and recovering an overhead vapor stream from said
further separation means, subjecting said overhead vapor stream
from said further separation means to indirect heat exchange for
additional cooling and partial condensation, and removing the
resultant condensate from said partial condensation as liquefied
natural gas product.
20. The process according to claim 1, wherein said process
comprises: subjecting at least a portion of said overhead gaseous
from the demethanizer column to heat exchange wherein said overhead
gaseous from the demethanizer column is used to cool at least one
other process stream, and then compressing the least a portion of
said overhead gaseous from the demethanizer column from the heat
exchange to form a residue gas; cooling at least portion of said
residue gas to obtain a cooled residue gas; introducing a part of
the cooled residue gas into said demethanizer column as a reflux
stream; and introducing another part of the cooled residue gas into
a further separation means, and recovering liquefied natural gas
product from said further separation means.
21. The process according to claim 1, wherein said process further
comprises: dividing said bottoms liquid stream from said gas/liquid
cold separator into at least a first portion and a second portion;
dividing said overhead gaseous stream from said gas/liquid cold
separator into at least a first portion and a second portion;
expanding said first portion of said bottoms liquid stream from
said gas/liquid cold separator and introducing the expanded first
portion of said bottoms liquid stream from said gas/liquid cold
separator into said demethanizer column at said intermediate point;
expanding said first portion of said overhead gaseous stream from
said gas/liquid cold separator and introducing the expanded first
portion of said overhead gaseous stream from said gas/liquid cold
separator into said upper region of said demethanizer column;
combining said second portion of said bottoms liquid stream from
said gas/liquid cold separator with said second portion of said
overhead gaseous stream from said gas/liquid cold separator;
cooling the resultant combined cold separator stream by indirect
heat exchange with at least a portion of said overhead vapor from
said demethanizer column, whereby the combined cold separator
stream is cooled and partially condensed and the overhead gaseous
stream from the top of said demethanizer column is heated; and
expanding the cooled resultant combined cold separator stream, and
then introducing the expanded cooled combined cold separator stream
into the top of said demethanizer column.
22. The process according to claim 5, wherein said process further
comprises introducing said liquid product stream removed from the
bottom of said demethanizer column into said main heat exchanger
for indirect heat exchange with said first partial stream of the
feed stream.
23. The process according to claim 5, wherein said process further
comprises: dividing said bottoms liquid stream from said gas/liquid
cold separator into at least a first portion and a second portion;
dividing said overhead gaseous stream from said gas/liquid cold
separator into at least a first portion and a second portion;
expanding said first portion of said bottoms liquid stream from
said gas/liquid cold separator and introducing the expanded first
portion of said bottoms liquid stream from said gas/liquid cold
separator into said demethanizer column at said intermediate point;
expanding said first portion of said overhead gaseous stream from
said gas/liquid cold separator and introducing the expanded first
portion of said overhead gaseous stream from said gas/liquid cold
separator into said upper region of said demethanizer column;
combining said second portion of said bottoms liquid stream from
said gas/liquid cold separator with said second portion of said
overhead gaseous stream from said gas/liquid cold separator;
cooling the resultant combined cold separator stream by indirect
heat exchange with at least a portion of said overhead vapor from
said demethanizer column, whereby the combined cold separator
stream is cooled and partially condensed and the overhead gaseous
stream from the top of said demethanizer is heated; and expanding
the cooled resultant combined cold separator stream, and then
introducing the expanded cooled combined cold separator stream into
the top of said demethanizer column.
24. The process according to claim 23, wherein said process further
comprises: after said overhead gaseous stream from the top of said
demethanizer column is subjected to indirect heat exchange with the
combined cold separator stream, further heating said overhead
gaseous stream from the top of said demethanizer by indirect heat
exchange with said second partial feed stream in said another heat
exchanger, and then compressing and removing at least a portion of
the overhead gaseous stream from said demethanizer as said residue
gas; introducing at least a portion of said residue gas stream from
the overhead gaseous stream of said demethanizer into said another
heat exchanger wherein the residue gas stream is cooled by indirect
heat exchange, and then subjecting the cooled residue gas stream to
further indirect heat exchange with said overhead gaseous stream
from the top of said demethanizer whereby the residue gas stream is
further cooled and partially liquefied; expanding a first portion
of the further cooled residue gas stream and introducing the
resultant partially liquefied first portion of the residue gas
stream into the upper region of said demethanizer as said reflux
stream; and introducing a second portion of the further cooled
residue gas stream into said further separation means, recovering
an overhead residue gas stream from said further separation means,
recovering a liquid stream from said further separation means as
said liquefied natural gas.
25. The process according to claim 21, wherein said process further
comprises: dividing said overhead vapor from said demethanizer
column into at least a first portion and a second portion, wherein
said second portion of said overhead vapor from said demethanizer
column forms said side stream; and using the first portion of said
overhead vapor from said demethanizer column to cool said resultant
combined cold separator stream by said indirect heat exchange,
whereby the combined cold separator stream is cooled and partially
condensed and the o first portion of overhead gaseous stream from
the top of said demethanizer column is heated.
26. The process according to claim 21, wherein said process further
comprises: after said overhead gaseous stream from the top of said
demethanizer column is subjected to indirect heat exchange with the
combined cold separator stream, further heating said overhead
gaseous stream from the top of said demethanizer by indirect heat
exchange with said second partial feed stream in said another heat
exchanger, and then compressing and removing at least a portion of
the overhead gaseous stream from said demethanizer as residue
gas.
27. The process according to claim 25, wherein said process further
comprises: after said overhead gaseous stream from the top of said
demethanizer column is subjected to indirect heat exchange with the
combined cold separator stream, further heating said overhead
gaseous stream from the top of said demethanizer by indirect heat
exchange with said second partial feed stream in said another heat
exchanger, and then compressing and removing at least a portion of
the overhead gaseous stream from said demethanizer as residue
gas.
28. The process according to claim 20, wherein said process further
comprises: introducing the cooled residue gas into a separation
means and recovering a residue liquid stream from said separation
means as said part of the cooled residue gas and recovering an
overhead gas stream from said separation means as said another part
of the cooled residue gas; introducing said part of the cooled
residue gas into the top region of said demethanizer as said reflux
stream; and cooling said another part of the cooled residue gas by
indirect heat exchange to produce a further cooled residue gas,
expanding said further cooled residue gas and introducing the
expanded further cooled residue gas into a said further separation
means, recovering an overhead stream from said further separation
means as a further residue gas, and recovering a liquid stream from
said further separation means as said liquefied natural gas
product.
29. The process according to claim 20, wherein said at least a
portion of said residue gas is cooled by indirect heat exchange
with at least a portion of the overhead gaseous stream of the
demethanizer column to form said cooled residue; expanding a
portion of the cooled residue gas stream to form said part of the
cooled residue gas and introducing said part of the cooled residue
gas into an upper region of said demethanizer column as said reflux
stream, and expanding another portion of the residue gas stream and
introducing the resultant expanded another portion as said another
part of the cooled residue gas into said further separation
means.
30. The process according to claim 20, wherein said at least a
portion of said residue gas is cooled by indirect heat exchange
with at least a portion of the overhead gaseous stream of the
demethanizer column to form said cooled residue; dividing said
cooled residue gas stream into at least a first portion and a
second portion expanding the first portion of the cooled residue
gas stream and introducing the resultant expanded first portion of
the cooled residue gas stream into an upper region of said
demethanizer, further cooling and partially condensing the second
portion of the cooled residue gas stream by indirect heat exchange,
and then introducing the cooled and partially condensed second
portion of the residue gas stream into a separation means,
recovering a residue liquid stream from said separation means and
introducing the residue liquid stream into the top region of said
demethanizer as said reflux stream; and recovering an overhead gas
stream from said separation means, cooling said overhead gas stream
from said separation means by indirect heat exchange, expanding the
further cooled overhead gas stream from said separation means and
introducing this expanded further cooled overhead gas stream from
said separation means into said further separation means.
31. The process for integrated liquefaction of natural gas and
recovery of natural gas liquids, said process comprising: cooling a
feed stream containing light hydrocarbons by indirect heat exchange
in a feed heat exchanger; introducing the cooled feed stream into a
gas/liquid cold separator, removing from said gas/liquid cold
separator an overhead gaseous stream and bottoms liquid stream, and
introducing said overhead gaseous stream and bottoms liquid stream
into a fractionation system, said fractionation system comprising a
demethanizer column; removing a liquid product stream from said
fractionation system; removing an overhead gaseous stream from said
fractionation system; generating a residue gas stream from said
overhead gaseous stream from said fractionation system; introducing
said residue gas stream into a further separation means, and
recovering from said further separation means a liquid product
stream and an overhead vapor stream; introducing either said liquid
product stream or said overhead vapor stream to an LNG
exchanger/separator; subjecting either said liquid product stream
or said overhead vapor stream to liquefaction in said LNG
exchanger/separator; and removing LNG liquid product from said LNG
exchanger/separator.
32. The process according to claim 31, said process further
comprising: splitting said overhead gaseous stream from said
gas/liquid cold separator into a first cold separator overhead
gaseous stream and a second cold separator overhead gaseous stream;
splitting said bottoms liquid stream from said gas/liquid cold
separator into a first cold separator bottoms liquid stream and a
second cold separator bottoms liquid stream; introducing said first
cold separator overhead gaseous stream and said cold separator
first bottoms liquid stream into said demethanizer; combining said
second cold separator overhead gaseous stream and said second cold
separator bottoms liquid stream; splitting an overhead gaseous
stream from said demethanizer into a first demethanizer overhead
gaseous stream and a second demethanizer overhead gaseous stream;
heating said first demethanizer overhead gaseous stream by indirect
heat exchange with the combined second cold separator overhead
gaseous stream and second cold separator bottoms liquid stream;
cooling said second demethanizer overhead gaseous stream by heat
exchange; introducing the cooled second demethanizer overhead
gaseous stream into said further separation means as said residue
gas; introducing said liquid product stream from said further
separation means into said demethanizer as said liquid reflux
stream; and introducing said gaseous vapor stream from said further
separation means into said LNG exchanger/separator.
33. The process according to claim 31, said process further
comprising: splitting said overhead gaseous stream from said
gas/liquid cold separator into a first cold separator overhead
gaseous stream and a second cold separator overhead gaseous stream;
splitting said bottoms liquid stream from said gas/liquid cold
separator into a first cold separator bottoms liquid stream and a
second cold separator bottoms liquid stream; introducing said first
cold separator overhead gaseous stream and said cold separator
first bottoms liquid stream into said demethanizer; combining said
second cold separator overhead gaseous stream and said second cold
separator bottoms liquid stream; heating an overhead gaseous stream
said demethanizer by indirect heat exchange with the combined
second cold separator overhead gaseous stream and second cold
separator bottoms liquid stream; heating and compressing the heated
overhead gaseous stream from said demethanizer column to produce
said residue gas; cooling said residue gas and introducing the
cooled residue gas into said further separation means; introducing
said liquid product stream from said further separation means into
said demethanizer as said liquid reflux stream; and introducing
said gaseous vapor stream from said further separation means into
said LNG exchanger/separator.
34. The process according to claim 31, wherein said fractionation
system comprises a demethanizer column, and said process further
comprises: splitting said feed stream containing light hydrocarbons
into a first partial feed stream and a second partial feed stream;
cooling said first partial feed stream in said feed heat exchanger
by indirect heat exchange; cooling said second partial feed stream
in another heat exchanger by indirect heat exchange; recombining
said first and second partial feed streams, and optionally cooling
the resultant recombined feed stream by heat exchange with a
refrigerant; and introducing the recombined feed stream into said
gas/liquid cold separator.
35. The process according to claim 34, wherein said fractionation
system comprises a demethanizer column, and said process further
comprises splitting said overhead gaseous stream from said
gas/liquid cold separator into a first cold separator overhead
gaseous stream and a second cold separator overhead gaseous stream;
splitting said bottoms liquid stream from said gas/liquid cold
separator into a first cold separator bottoms liquid stream and a
second cold separator bottoms liquid stream; expanding said first
cold separator overhead gaseous stream and introducing the expanded
first cold separator overhead gaseous stream into an upper region
of said demethanizer column; expanding said cold separator first
bottoms liquid stream and introducing the expanded cold separator
first bottoms liquid stream into an intermediate region of said
demethanizer; and combining said second cold separator overhead
gaseous stream and said second cold separator bottoms liquid
stream.
36. The process for integrated liquefaction of natural gas and
recovery of natural gas liquids, said process comprising: cooling a
feed stream (1) containing light hydrocarbons by indirect heat
exchange in a feed heat exchanger (2);introducing the cooled feed
stream into a gas/liquid cold separator (3), removing from said
gas/liquid cold separator (3) an overhead gaseous stream (4) and
bottoms liquid stream (8), and introducing said overhead gaseous
stream (4) and bottoms liquid stream (8) into a fractionation
system, said fractionation system comprising a demethanizer column;
removing a liquid product stream (15) of natural gas liquids from
said fractionation system; removing an overhead gaseous stream (12)
from said fractionation system; generating a residue gas stream
(23, 59) from said overhead gaseous stream from said fractionation
system; cooling (48) said residue gas stream, introducing the
cooled residue gas stream into a further gas/liquid separator or
further distillation column (26), and removing from said further
gas/liquid separator or further distillation column (26) a liquid
stream (27) and an overhead vapor stream (28); introducing said
liquid stream (27) from said further gas/liquid separator or
further distillation column (26) into said light ends fractionation
column (7), said heavy ends fractionation column (9) or said
demethanizer (62) of said fractionation system as a liquid reflux
stream; introducing said overhead vapor stream (28) from said
further gas/liquid separator or further distillation column (26) to
a heat exchanger (48) wherein said overhead vapor stream is cooled;
introducing the cooled overhead vapor stream (29) into a separator
(50); and removing a liquid product of liquefied natural gas from
said separator.
Description
[0001] The invention relates to an integrated process and apparatus
for liquefaction of natural gas and recovery of natural gas
liquids. In particular, the improved process and apparatus reduces
the energy consumption of a Liquefied Natural Gas (LNG) unit by
using a portion of the already cooled overhead vapor from a
fractionation column (e.g., a light-ends fractionation column
(LEFC) or a demethanizer/de-ethanizer) from an NGL (natural gas
liquefaction) unit to, depending upon composition, provide, for
example, reflux for fractionation in the NGL unit and/or a cold
feed for the LNG unit, or by cooling, within the NGL unit (e.g.,
via a standalone refrigeration system), a residue gas originating
from a fractionation column of the NGL unit and using the resultant
cooled residue gas to, depending upon composition, provide, for
example, reflux/feed for fractionation in the NGL and/or a cold
feed for the LNG unit, thereby reducing the energy consumption of
the LNG unit and rendering the process more energy-efficient.
[0002] Natural gas is an important commodity throughout the world,
as both an energy source and a source a raw materials. Worldwide
natural gas consumption is expected to rise from 110.7 trillion
cubic feet in 2008 to 123 trillion cubic feet in 2015, and 168.7
trillion cubic feet in 2035 [U.S Energy Information Administration,
International Energy Outlook 2011, Sep. 19, 2011, Report Number
DOE/EIA-0484(2011)].
[0003] Natural gas obtained from oil and gas production wellheads
mainly contains methane, but also may contain hydrocarbons of
higher molecular weight including ethane, propane, butane, pentane,
their unsaturated analogs, and heavy hydrocarbons including
aromatics (e.g., benzene). Natural gas often also contains
non-hydrocarbon impurities such as water, hydrogen, nitrogen,
helium, argon, hydrogen sulfide, carbon dioxide, and/or
mercaptans.
[0004] Before being introduced into high pressure gas pipelines for
delivery to consumers, natural gas is treated to remove impurities
such as carbon dioxide and sulfur compounds. In addition, the
natural gas may be treated to remove a portion of the natural gas
liquids (NGL). These include lighter hydrocarbons, namely ethane,
propane, and butane, as well as the heavier C5+ hydrocarbons. Such
treatment yields a leaner natural gas, which the consumer may
require, but also provides a source of valuable materials. For
example, the lighter hydrocarbons can be used as feedstock for
petrochemical processes and as fuel. The C5+ hydrocarbons can be
used in gasoline blending.
[0005] Often factors such as the location of the wellhead and/or
the absence of requisite infrastructure may preclude the
possibility of transporting natural gas via pipeline. In such
cases, the natural gas can be liquefied (LNG) and transported in
liquid form via a cargo carrier (truck, train, ship). However,
during liquefaction of natural gas by cryogenic processes, heavier
hydrocarbons within the natural gas can solidify which can then
lead to damage to the cryogenic equipment and interruption of the
liquefaction process. Thus, in this case also it is desirable to
remove heavier hydrocarbons from the natural gas.
[0006] Numerous processes are known for the recovery of natural gas
liquids. For example, Buck (U.S. Pat. No. 4,617,039) describes a
process wherein a natural gas feed stream is cooled, partially
condensed, and then separated in a high pressure separator. The
liquid stream from the separator is warmed and fed into the bottom
of a distillation (deethanizer) column. The vapor stream from the
separator is expanded and introduced into a separator/absorber.
Bottom liquid from separator/absorber is used as liquid feed for
the deethanizer column. The overhead stream from the deethanizer
column is cooled and partially condensed by heat exchange with the
vapor stream removed from the top of the separator/absorber. The
partially condensed overhead stream from the deethanizer column is
then introduced into the upper region of the separator/absorber.
The vapor stream removed from the top of the separator/absorber can
be further warmed by heat exchange and compressed to provide a
residue gas which, upon further compression, can be reintroduced
into a natural gas pipeline.
[0007] Other C2+ and/or C3+ recovery processes are known in which
the fed gas is subjected to cooling and expansion to yield a vapor
stream that is introduced into the bottom region of a light ends
fractionation column and a liquid stream that is introduced into a
high ends fractionation column. Residue gas is removed from the top
of the light ends fractionation column and product liquid is
removed from the bottom of the high ends fractionation column.
Liquid from the bottom of the light ends fractionation column is
fed to the upper region of the heavy ends fractionation column.
Overhead vapor from the heavy ends fractionation column is
partially condensed and the condensate portion is used as reflux in
the light ends fractionation column. The gaseous portion may be
combined with the residue gas. See, for example, Buck et al. (U.S.
Pat. No. 4,895,584), Key et al. (U.S. Pat. No. 6,278,035), Key et
al. (U.S. Pat. No. 6,311,516), and Key et al. (U.S. Pat. No.
7,544,272).
[0008] Further, there are many known processes for liquefaction of
natural gas. Typically, the natural gas is distilled in a
demethanizer and the resultant methane-enriched gas is subjected to
cooling and expansion to produce LNG product. The bottom liquid
from the demethanizer can be sent for further processing for
recovery of natural gas liquids. See, for example, Shu et al. (U.S.
Pat. No. 6,125,653), Wilkinson et al. (U.S. Pat. No. 6,742,358),
Wilkinson et al. (U.S. Pat. No. 7,155,931), Wilkinson et al. (U.S.
Pat. No. 7,204,100), Cellular et al. (U.S. Pat. No. 7,216,507),
Cellular et al. (U.S. Pat. No. 7,631,516), Wilkinson et al. (US
2004/0079107). In other systems, the natural gas is cooled and
partially liquefied and then separated in a gas/liquid separator.
The resultant gas and liquid streams are both used as feeds to a
demethanizer. A liquid products stream is removed from the bottom
of the demethanizer, and the vapor stream removed from the top of
the demethanizer, after providing cooling to process streams, is
removed as residue gas. See, for example, Campbell et al. (U.S.
Pat. No. 4,157,904) and Campbell et al. (U.S. Pat. No.
5,881,569).
[0009] In addition, many attempts have been made to integrate a NGL
recovery process with a LNG process for liquefaction of natural
gas. See, for example, Houshmand et al. (U.S. Pat. No. 5,615,561),
Campbell et al. (U.S. Pat. No. 6,526,777), Wilkinson et al. (U.S.
Pat. No. 6,889,523), Qualls et al. (US 2007/0012072), Mak et al.
(US 2007/0157663), Mak (US 2008/0271480), and Roberts et al. (US
2010/0024477).
[0010] However, while these processes provide some integration of
NGL recovery and LNG production, improvements are still needed with
regards to achieving such integration in a simple and efficient
manner, particularly in a manner which reduces energy
consumption.
[0011] Therefore, an aspect of the present invention is to provide
a process and apparatus which integrate NGL recovery and LNG
production in a cost effective manner, and in particular reduces
the energy consumption of the LNG production.
[0012] In particular, the invention provides improvements to NGL
recovery processes, such as the CRYO-PLUS.TM. process (see, e.g.,
Buck (U.S. Pat. No. 4,617,039), Key et al. (U.S. Pat. No.
6,278,035), and Key et al. (U.S. Pat. No. 7,544,272)), the Gas
Subcooled (GSP) process (see, e.g., Campbell et al. (U.S. Pat. No.
4,157,904)), and the Recycle Split Vapor (RSV) process (see, e.g.,
Campbell et al. (U.S. Pat. No. 5,881,569), that is improvements
which integrate these NGL recovery processes with an LNG production
process.
[0013] The specification provides other aspects and advantages of
the invention.
[0014] These aspects are achieved, according to the invention, by
using a side stream of the already cooled overhead vapor from a
fractionation column of an NGL recovery unit, such as a light ends
fractionation column or a demethanizer/de-ethanizer, to, depending
upon composition, provide reflux for fractionation in the NGL
and/or a cold feed for the LNG unit, thereby reducing the energy
consumption of the LNG production unit while having a minimal
impact on the NGL recovery unit. Alternatively, these aspects are
achieved by cooling, within the NGL unit (e.g., via a standalone
refrigeration system), a residue gas originating from a
fractionation column of the NGL unit and using the resultant cooled
residue gas to, depending upon composition, provide reflux/feed for
fractionation in the NGL and/or a cold feed for the LNG unit,
thereby reducing the energy consumption of the LNG unit and
rendering the process more energy-efficient.
[0015] Although the inventive processes and apparatuses are
generally described herein as being suitable for the treatment of
natural gas, i.e., gas resulting from oil or gas production wells,
the invention is suitable for treating any feed stream which
contains a predominant amount of methane along with other light
hydrocarbons such as ethane, propane, butane and/or pentane.
[0016] In general, the invention provides a process and an
apparatus wherein a feed stream containing light hydrocarbons
(e.g., a natural gas feed stream) is processed in a natural gas
liquefaction recovery (NGL) unit that comprises a main heat
exchanger, a cold separator, and a fractionation system comprising
either (a) a light ends fractionation column and a heavy ends
fractionation column, or (b) a demethanizer/de-ethanizer, wherein
at least a part of the overhead vapor stream originating from the
fractionation system of the NGL unit (e.g., a part of already
overhead or residue gas that is cooled by supplemental
refrigeration) is used , depending upon composition, provide
reflux/feed for fractionation in the NGL and/or a cold feed for the
LNG unit.
[0017] According to a general process aspect of the invention there
is provided a process comprising:
[0018] cooling a feed stream containing light hydrocarbons (e.g., a
natural gas feed stream) in one or more heat exchangers, wherein
the feed stream is cooled and partially condensed by indirect heat
exchange;
[0019] introducing the partially condensed feed stream into a
gas/liquid cold separator to produce an overhead gaseous stream and
bottoms liquid stream which are to be introduced into a
fractionation system comprising (a) a light ends fractionation
column and a heavy ends fractionation column, or (b) a demethanizer
(or deethanizer) column;
[0020] expanding at least a portion of the overhead gaseous stream
from the gas/liquid cold separator and introducing this expanded
overhead gaseous stream into (a) a lower region of a light ends
fractionation column or (b) an upper region of a demethanizer (or
deethanizer) column;
[0021] introducing at least a portion of the bottoms liquid stream
from the gas/liquid cold separator into (a) a heavy ends
fractionation column at an intermediate point thereof or (b) a
demethanizer (or deethanizer) column at an intermediate point
thereof;
[0022] removing a liquid product stream from the bottom of (a) the
heavy ends fractionation column or (b) the bottom of the
demethanizer (or deethanizer) column;
[0023] removing a overhead gaseous stream from the top of (a) the
light ends fractionation column or (b) the demethanizer (or
deethanizer) column; and
[0024] if the fractionation system comprises a light ends
fractionation column and a heavy ends fractionation column,
removing a bottoms liquid stream from a lower region of the light
ends fractionation column, and introducing this bottoms liquid
stream from the light ends fractionation column into an upper
region of the heavy ends fractionation column;
[0025] (a) when the fractionation system comprises a light ends
fractionation column and a heavy ends fractionation column, [0026]
(i) subjecting a first portion of the overhead gaseous stream from
the light ends fractionation column to indirect heat exchange
(e.g., in a subcooler) with an overhead gaseous stream removed from
the top of the heavy ends fractionation column, whereby the
overhead gaseous stream from the top of the heavy ends
fractionation column is cooled and partially condensed, and
introducing this cooled and partially condensed overhead gaseous
stream from the top of the heavy ends fractionation column into the
light ends fractionation column; [0027] (ii) removing a second
portion of the overhead gaseous stream from the light ends
fractionation column as a side stream, and subjecting the side
stream to indirect heat exchange for further cooling, and partially
liquefying the side stream; [0028] (iii) introducing the partially
liquefied side stream into a further separation means, recovering
liquid product from the further separation means and introducing
the recovered liquid product into the light ends fractionation
column as a liquid reflux stream and/or into the heavy ends
fractionation column as a liquid reflux stream, [0029] (iv)
recovering an overhead vapor stream from the further separation
means, subjecting this overhead vapor stream to indirect heat
exchange for additional cooling and partial condensation, and
feeding the resultant vapor and condensate to an LNG separator
wherein a LNG liquid product is produced; and [0030] (v) recovering
an overhead vapor stream from the further separation means,
compressing this overhead vapor stream to form a residue gas;
or
[0031] (b) when the fractionation system comprises a light ends
fractionation column and a heavy ends fractionation column, [0032]
(i) subjecting the overhead gaseous stream from the light ends
fractionation column to indirect heat exchange (e.g., in a
subcooler) with an overhead gaseous stream removed from the top of
the heavy ends fractionation column, whereby the overhead gaseous
stream from the light ends fractionation column is heated and the
overhead gaseous stream from the top of the heavy ends
fractionation column is cooled and partially condensed, and
introducing this cooled and partially condensed overhead gaseous
stream from the top of the heavy ends fractionation column into the
light ends fractionation column; [0033] (ii) further heating and
compressing the overhead gaseous stream from the light ends
fractionation column to produce a residue gas; [0034] (iii) cooling
at least a portion of the residue gas whereby the portion of the
residue gas is partially liquefied; [0035] (iv) introducing an
expanded portion of the partially liquefied residue gas into the
light ends fractionation column; [0036] (vi) expanding another
portion of the partially liquefied residue gas and introducing this
expanded portion into a further separation means; [0037] (vii)
recovering liquid product from the further separation means as LNG
liquid product; and [0038] (viii) recovering an overhead vapor
stream from the further separation means, and compressing this
overhead vapor stream to form a residue gas; or
[0039] (c) when the fractionation system comprises a demethanizer
(or deethanizer) column, [0040] (i) subjecting a first portion of
the overhead gaseous stream from the demethanizer (or deethanizer)
column to indirect heat exchange (e.g., in a subcooler) with a
stream obtained by combining a portion of the overhead gaseous
stream from the gas/liquid cold separator and a portion of the
bottoms liquid stream from the gas/liquid cold separator; [0041]
(ii) removing a second portion of the overhead gaseous from the
demethanizer (or deethanizer) column as a side stream, and
partially liquefying the side stream by heat exchange; [0042] (iii)
introducing the partially liquefied side stream into a further
separation means, recovering liquid product from the further
separation means and introducing the recovered liquid product into
the demethanizer (or deethanizer) column as a liquid reflux stream,
and [0043] (iv) recovering an overhead vapor stream from the
further separation means, subjecting this overhead vapor stream to
indirect heat exchange for additional cooling and partial
condensation, and removing the resultant condensate as an LNG
liquid product; or
[0044] (d) when the fractionation system comprises a demethanizer
(or deethanizer) column, [0045] (j) subjecting the overhead gaseous
stream from the demethanizer (or deethanizer) column to indirect
heat exchange (e.g., in a subcooler) with a stream obtained by
combining a portion of the overhead gaseous stream from the
gas/liquid cold separator and a portion of the bottoms liquid
stream from the gas/liquid cold separator; [0046] (ii) further
heating and compressing the overhead gaseous stream from the
demethanizer (or deethanizer) column to produce a residue gas;
[0047] (iii) cooling at least a portion of the residue gas whereby
the portion of the residue gas is partially liquefied; [0048] (iv)
introducing this partially liquefied residue gas into a further
separation means; [0049] (v) recovering liquid product from the
further separation means and introducing the recovered liquid
product as reflux to the demethanizer (or deethanizer) column;
[0050] (vi) recovering an overhead vapor stream from the further
separation means, cooling this overhead vapor stream whereby the
overhead vapor stream is partially liquefied; [0051] (vii)
introducing this partially liquefied overhead vapor stream into
another further separation means; and [0052] (viii) recovering
liquid product from the another further separation means as an LNG
product.
[0053] In accordance with a first process aspect of the invention,
there is provided a process comprising:
[0054] introducing a feed stream containing light hydrocarbons
(e.g., a natural gas feed stream) into a main heat exchanger (e.g.,
a plate-fin heat exchanger or shell and tube heat exchanger)
wherein the feed stream is cooled and partially condensed by
indirect heat exchange;
[0055] introducing the partially condensed feed stream into a
gas/liquid cold separator producing an overhead gaseous stream and
bottoms liquid stream;
[0056] expanding the overhead gaseous stream from the gas/liquid
cold separator and then introducing the expanded overhead gaseous
stream into a lower region of a light ends fractionation
column;
[0057] introducing the bottoms liquid stream from the gas/liquid
cold separator into a heavy ends fractionation column at an
intermediate point thereof;
[0058] removing a liquid product stream from the bottom of the
heavy ends fractionation column and introducing the liquid product
stream into the main heat exchanger where it undergoes indirect
heat exchanger with the feed stream;
[0059] removing a bottoms liquid stream from a lower region of the
light ends fractionation column, and introducing the bottoms liquid
stream from the light ends fractionation column into an upper
region of the heavy ends fractionation column;
[0060] removing a overhead gaseous stream from the top of the light
ends fractionation column, and subjecting a first portion of this
overhead gaseous stream to indirect heat exchange (e.g., in a
subcooler) with an overhead gaseous stream removed from the top of
the heavy ends fractionation column, whereby the overhead gaseous
stream from the top of the heavy ends fractionation column is
cooled and partially condensed, and discharging the first portion
of the second overhead gaseous stream from the light ends
fractionation column as residue gas;
[0061] removing a bottoms liquid stream from a lower region of the
heavy ends fractionation column, heating the bottoms liquid stream
from the heavy ends fractionation column by indirect heat exchange
and returning the bottoms liquid stream from the heavy ends
fractionation column to the lower region of the heavy ends
fractionation column as a reboiler stream;
[0062] introducing the cooled and partially condensed overhead
gaseous stream from the top of the heavy ends fractionation column
into the light ends fractionation column;
[0063] removing a second portion of the overhead gaseous from the
light ends fractionation column as a side stream, partially
liquefying the side stream across a flow-control valve, and
subjecting the partially liquefied side stream to indirect heat
exchange with a refrigerant fluid for further cooling,
[0064] introducing the partially liquefied side stream into a
further separation means (e.g., a further gas/liquid separator or a
further distillation column), recovering liquid product (containing
the majority of ethane, as well as heavier hydrocarbon components,
of the partially liquefied side stream) and introducing the
recovered liquid product into the light ends fractionation column
as a liquid reflux stream and/or into the heavy ends fractionation
column as a liquid reflux stream, and
[0065] recovering an overhead vapor stream rich in methane, from
the further separation means, subjecting the overhead vapor stream
to indirect heat exchange with a refrigerant fluid for additional
cooling and partial condensation, feeding the resultant condensate
to an LNG exchanger, where liquefaction is performed.
[0066] The LNG process may be an industry standard mixed
refrigerant or nitrogen refrigeration process. Thus, in the process
according to the invention, a single refrigerant stream may be used
to provide the cooling necessary to liquefy the natural gas into
LNG. In a typical LNG process, a refrigerant cycle compressor
increases the pressure of the circulating refrigerant. This high
pressure refrigerant is cooled via exchange with air, water or
other cooling media. The resulting cool, high pressure refrigerant,
often present in both a liquid and gas phase, passes through the
LNG exchanger where the refrigerant is fully liquefied or becomes a
cooled vapor at high pressure. The cold refrigerant is then reduced
in pressure via a Joule-Thomson valve (isenthalpic, i.e., a process
that generally proceeds without any change in enthalpy) or via a
turboexpander (isentropic, i.e., a process that generally proceeds
without any change in entropy) to a lower pressure resulting in the
flashing of the cold, high pressure refrigerant into a two-phase
vapor and liquid mixture or single phase vapor that is colder than
the preceding stream and is also colder in temperature than the
liquefaction point (bubble point) of the LNG feed stream. This low
pressure, cold, two-phase vapor and liquid mixture or single phase
vapor refrigerant stream returns to the LNG exchanger to provide
sufficient liquefaction cooling for both the refrigerant as well as
the natural gas feed stream that is to be liquefied. Along the
course of flowing through the LNG exchanger, the refrigerant stream
is fully vaporized. This vapor flows to the refrigerant cycle
compressor to begin the cooling cycle again.
[0067] Thus, in accordance with the invention, when a refrigerant
system is used to cool a residue gas stream or a side stream from
the overhead vapors of light ends fractionation column or a
demethanizer, the refrigerant system can involve the use of a
single refrigerant system or mixed refrigerant cooling system or an
expander based system or a combination of a mixed refrigerant
system and an expander based refrigeration system.
[0068] Additionally, the refrigerant system can use a refrigerant
composition: either it is a pure single refrigerant (concentration
>95 vol %) or a mixture of two or more components with
concentrations >5 vol % each. Suitable refrigerant components
include light paraffinic or olefinic hydrocarbons like methane,
ethane, ethylene, propane, propylene, butane, pentane, and
inorganic components like nitrogen, argon as well as possibly
carbon monoxide, carbon dioxide, hydrogen sulfide, ammonia.
Further, the refrigerant system can involve (a) a closed or open
loop refrigeration cycle, (b) two or more pressure levels in the
entire refrigeration cycle, (c) pressure reduction from a higher
pressure to a lower pressure either via work expansion (turbo
expander) and/or via isenthalpic throttling (control valve,
restriction orifice), or (d) phase condition of the refrigerant
either all vapor phase or changing from vapor to liquid and back to
vapor. For example, this refrigeration system can utilize (a) a
phase-change mixed refrigerant cycle without work expansion of a
high pressure gas fraction, (b) a phase-change mixed refrigerant
cycle with work expansion of a high pressure gas fraction, (c) a
vapor phase mixed refrigerant cycle with work expansion of a high
pressure gas fraction in one or more stages, or (d) a vapor phase
pure refrigerant cycle with work expansion of a high pressure gas
fraction in one or more stages.
[0069] In the description herein and in the drawings, expansions of
fluids are often characterized as being performed by an expansion
valve or "expansion across a valve." One skilled in the art would
recognize that these expansion can be performed using various types
expansion devices such as an expander, a control valve, a
restrictive orifice or other device intended to reduce the pressure
of the circulating fluid. The use of these expansion devices to
perform the expansions described herein is included within the
scope of the invention.
[0070] By removing a side stream from the overhead gaseous stream
of the light ends fractionation column, cooling and partially
condensing this side stream, and then delivering at least part of
the resulting condensate to an LNG exchanger, an integration of the
NGL and LNG processes is achieved in a manner which does not
compromise the NGL recovery process. The utilization of a portion
of the cold overhead gaseous stream from the LEFC of the NGL
process reduces refrigeration requirements of the LNG process,
thereby reducing overall energy consumption, and improving
recoveries for both processes.
[0071] According to one embodiment of the invention, the liquid
product recovered from the further separation means (e.g., further
distillation column) is introducing into the light ends
fractionation column as a liquid reflux stream. According to
another embodiment of the invention, the liquid product recovered
from the further separation means (e.g., further distillation
column) is introducing into the heavy ends fractionation column as
a liquid reflux stream.
[0072] In accordance with a second process aspect of the invention,
there is provided a further process comprising:
[0073] introducing a feed stream containing light hydrocarbons
(e.g., a natural gas feed stream) into a main heat exchanger (e.g.,
a plate-fin heat exchanger or shell and tube heat exchanger)
wherein the feed stream is cooled and partially condensed by
indirect heat exchange;
[0074] introducing the partially condensed feed stream into a
gas/liquid cold separator producing an overhead gaseous stream and
bottoms liquid stream;
[0075] expanding the overhead gaseous stream from the gas/liquid
cold separator and then introducing the expanded overhead gaseous
stream into a lower region of a light ends fractionation
column;
[0076] introducing the bottoms liquid stream from the gas/liquid
cold separator into a heavy ends fractionation column at an
intermediate point thereof;
[0077] removing a liquid product stream from the bottom of the
heavy ends fractionation column and introducing the liquid product
stream from the bottom of the heavy ends fractionation column into
the main heat exchanger where it undergoes indirect heat exchanger
with the feed stream;
[0078] removing a bottoms liquid stream from a lower region of the
light ends fractionation column, and introducing the bottoms liquid
stream from the light ends fractionation column into an upper
region of the heavy ends fractionation column;
[0079] removing a overhead gaseous stream from the top of the light
ends fractionation column, and subjecting this overhead gaseous
stream to indirect heat exchange (e.g., in a subcooler) with an
overhead gaseous stream removed from the top of the heavy ends
fractionation column, whereby the overhead gaseous stream from the
top of the heavy ends fractionation column is cooled and partially
condensed, and then discharging the overhead gaseous stream from
the light ends fractionation column as residue gas;
[0080] removing a bottoms liquid stream from a lower region of the
heavy ends fractionation column, heating the bottoms liquid stream
from the heavy ends fractionation column by indirect heat exchange
and returning the bottoms liquid stream from the heavy ends
fractionation column to the lower region of the heavy ends
fractionation column as a reboiler stream;
[0081] introducing the cooled and partially condensed overhead
gaseous stream from the top of the heavy ends fractionation column
into the light ends fractionation column;
[0082] introducing a residue gas stream into the main heat
exchanger wherein the residue gas stream is cooled by indirect heat
exchange, and then subjecting the cooled residue gas stream to
further indirect heat exchange (e.g., in the subcooler) with an
overhead gaseous stream removed from the top of the heavy ends
fractionation column whereby the residue gas stream is further
cooled; [0083] expanding the further cooled residue gas stream and
introducing the resultant partially liquefied residue gas stream
into a further separation means (e.g., a further gas/liquid
separator or a further distillation column), recovering an overhead
residue gas stream from the further separation means, recovering a
liquid stream from the further separation means and feeding this
liquid stream to an LNG exchanger, where liquefaction is
performed.
[0084] In accordance with a third process aspect of the invention,
there is provided a further process comprising:
[0085] introducing a feed stream containing light hydrocarbons
(e.g., a natural gas feed stream) into a main heat exchanger (e.g.,
a plate-fin heat exchanger or shell and tube heat exchanger)
wherein the feed stream is cooled and partially condensed by
indirect heat exchange;
[0086] introducing the partially condensed feed stream into a
gas/liquid cold separator producing an overhead gaseous stream and
bottoms liquid stream;
[0087] expanding the overhead gaseous stream from the gas/liquid
cold separator and then introducing the expanded overhead gaseous
stream from the gas/liquid cold separator into a lower region of a
light ends fractionation column;
[0088] introducing the bottoms liquid stream from gas/liquid cold
separator into a heavy ends fractionation column at an intermediate
point thereof;
[0089] removing a liquid product stream from the bottom of the
heavy ends fractionation column and introducing the liquid product
stream from the bottom of the heavy ends fractionation column into
the main heat exchanger where it undergoes indirect heat exchanger
with the feed stream;
[0090] removing a bottoms liquid stream from a lower region of the
light ends fractionation column, and introducing the bottoms liquid
stream from the light ends fractionation column into an upper
region of the heavy ends fractionation column;
[0091] removing a overhead gaseous stream from the top of the light
ends fractionation column, and subjecting this overhead gaseous
stream to indirect heat exchange (e.g., in a subcooler) with an
overhead gaseous stream removed from the top of the heavy ends
fractionation column, whereby the overhead gaseous stream from the
top of the heavy ends fractionation column is cooled and partially
condensed;
[0092] removing a bottoms liquid stream from a lower region of the
heavy ends fractionation column, heating the bottoms liquid stream
from the heavy ends fractionation column by indirect heat exchange
and returning the bottoms liquid stream from the heavy ends
fractionation column to the lower region of the heavy ends
fractionation column as a reboiler stream;
[0093] introducing the cooled and partially condensed overhead
gaseous stream from the top of the heavy ends fractionation column
into the light ends fractionation column;
[0094] introducing the overhead gaseous stream from the light ends
fractionation column, after being heated by heat exchange and
compressed, as a residue gas into a heat exchanger wherein the
residue gas is cooled and partially liquefied by indirect heat
exchange; and
[0095] introducing the resultant partially liquefied residue gas
stream into a further separation means (e.g., a further gas/liquid
separator or a further distillation column), recovering a liquid
stream from the further separation means which is introduced into
the light ends fractionation column as reflux, recovering an
overhead residue gas stream from the further separation means, and
feeding at least a portion of the overhead residue gas stream from
the further separation means to an LNG exchanger where liquefaction
is performed.
[0096] According to a further embodiment of the above described
processes, the bottoms liquid stream removed from the lower region
of the heavy ends fractionation column that is recycled as a
reboiler stream is heated in the main heat exchanger by indirect
heat exchange with the feed stream (e.g., natural gas), before
being returned to the lower region of the heavy ends fractionation
column.
[0097] In addition, a further liquid stream can be removed from an
intermediate point of the heavy ends fractionation column and also
used for cooling the natural gas feed stream in the main heat
exchanger. The further liquid stream is removed from a first
intermediate point of the heavy ends fractionation column, heated
by indirect heat exchange with the natural gas feed stream in the
main heat exchanger, and then reintroduced into the heavy ends
fractionation column at another intermediate point below the first
intermediate point.
[0098] According to another embodiment of the invention, additional
reflux streams are provided for the light ends fractionation
column. A portion of the gaseous overhead stream removed from the
top of cold separator, prior to expansion, is fed to a subcooler
where it undergoes indirect heat exchange with the overhead vapor
from the light ends fractionation column. This portion of the
gaseous overhead stream is cooled and partially liquefied in the
subcooler and introduced into the top region of the light ends
fractionation column to provide additional reflux.
[0099] Additionally or alternatively, a portion of bottoms liquid
stream from the gas/liquid cold separator is delivered to a
liquid/liquid heat exchanger where it undergoes indirect heat
exchange with the bottom liquid stream removed from the light ends
fractionation column. Thereafter, the stream is then fed to an
intermediate region of the light ends fractionation column as a
liquid reflux. Each of these two additional reflux streams improves
recovery of ethane and heavier hydrocarbon components.
[0100] In accordance with a further embodiment an additional reflux
for the light ends fractionation column is provided through a
combination of a portion of the gaseous overhead stream removed
from the top of cold separator and a portion of bottoms liquid
stream from cold separator. In this embodiment, prior to expansion,
a portion of the gaseous overhead stream removed from the top of
cold separator is combined with a portion of bottoms liquid stream
from cold separator, and the combined stream is fed to the
subcooler. In the subcooler it undergoes indirect heat exchange
with the overhead vapor from light ends fractionation column. The
combined stream is cooled and partially liquefied in the subcooler
and introduced into the top region of the light ends fractionation
column to provide additional reflux. This additional reflux stream
for the light ends fractionation column improves recovery of ethane
and heavier hydrocarbon components.
[0101] In one version of the above mentioned embodiment, the side
stream from the overhead gaseous stream of the light ends
fractionation column is eventually introduced into the light ends
fractionation column. According to a modification, the side stream
from the overhead gaseous stream of the light ends fractionation
column is eventually introduced into the heavy ends fractionation
column, rather than the light ends fractionation column. As
described previously, the side stream is partially liquefied across
a flow-control valve. The partially liquefied vapor undergoes
indirect heat exchange with a refrigerant fluid for further cooling
and is then fed into the further distillation column. The
methane-rich overhead vapor stream from the further separation
means (e.g., further distillation column) undergoes indirect heat
exchange with the refrigerant fluid for additional cooling, and is
then fed into the LNG exchanger, where liquefaction occurs. The
majority of ethane as well as heavier hydrocarbon components are
recovered from the bottom of the further separation means (e.g.,
further distillation column) as liquid product. This liquid product
is introduced into the top of the heavy ends fractionation column
as a liquid reflux stream.
[0102] According to a further embodiment of the invention, the
system can incorporate a refrigeration loop through the NGL process
which results in a reduction in energy consumption. For example, a
stream of refrigerant fluid from the refrigerant system is fed
through the main heat exchanger where it undergoes indirect heat
exchange with the natural gas feed stream and possibly other
streams (e.g., the liquid product stream from the bottom of the
heavy ends fractionation column, the further liquid stream from an
intermediate point of the heavy ends fractionation column, the
reboiler stream removed from the bottom region of the heavy ends
fractionation column, and/or the overhead vapor product stream
removed from the top of the light ends fractionation column). The
refrigerant stream is cooled and partially liquefied in the main
heat exchanger and is then introduced into the subcooler where it
is further cooled and liquefied. The refrigerant stream is then
flashed across a valve, causing the fluid to reach even colder
temperatures, and is then fed back to the subcooler to provide
cooling for the additional reflux streams of the light ends
fractionation column. The refrigerant stream then returns to the
main heat exchanger, where it functions as a coolant for the NGL
process streams. Thereafter, the refrigerant stream is returned to
the refrigeration system for compression.
[0103] According to a further embodiment, a modified refrigeration
loop is used. A stream of refrigerant fluid from the refrigerant
system is fed through the main heat exchanger where it undergoes
indirect heat exchange with the natural gas feed stream and
possibly other streams (e.g., the liquid product stream from the
bottom of the heavy ends fractionation column, the further liquid
stream from an intermediate point of the heavy ends fractionation
column, the reboiler stream removed from the bottom region of the
heavy ends fractionation column, and/or the overhead vapor product
stream removed from the top of the light ends fractionation
column). In the main heat exchanger, the refrigerant stream is
cooled and partially liquefied and is then introduced into the
subcooler where it is further cooled and liquefied. This stream is
then introduced into the heat exchanger used for cooling the side
stream of the overhead vapor product stream from the light ends
fractionation column. The refrigerant stream exits the heat
exchanger and is flashed across a valve, causing the fluid to reach
even colder temperatures. The resultant stream is then fed back to
the same heat exchanger to provide further cooling. Thereafter, the
refrigerant passes through the subcooler and then into the main
heat exchanger, where it serves as a coolant to the NGL process
streams. The refrigerant stream then flows back to the
refrigeration system for compression.
[0104] According to a further embodiment, a residue gas stream is
recovered from the partially condensed overhead vapor stream
obtained from the further separation means, and this residue gas
stream is used to cool, by indirect heat exchange, the overhead
vapor stream from the further separation means and/or the side
stream of the overhead vapor product stream from the light ends
fractionation column. Thereafter, the residue gas stream can be
compressed to the desired pressure. According to a further
modification, the residue gas stream can be compressed and then
optionally used for indirect heat exchange with the overhead vapor
stream from the further separation means and/or the side stream of
the overhead vapor product stream from the light ends fractionation
column.
[0105] In accordance with a fourth process aspect of the invention,
there is provided a further process comprising:
[0106] splitting a feed stream containing light hydrocarbons (e.g.,
a natural gas feed stream) into at least a first partial stream and
a second partial stream;
[0107] introducing the first partial stream of the feed stream into
a main heat exchanger (e.g., a plate-fin heat exchanger or shell
and tube heat exchanger) wherein the first partial stream of the
feed stream is cooled and partially condensed by indirect heat
exchange;
[0108] introducing the second partial stream of the feed stream
into a heat exchanger wherein the second partial stream of the feed
stream is cooled and partially condensed by indirect heat
exchange;
[0109] recombining the first and second partial streams of the feed
stream, and optionally subjecting the resultant recombined feed
stream to heat exchange with a refrigerant (e.g., a propane
refrigerant);
[0110] introducing the cooled recombined feed stream into a
gas/liquid cold separator to produce an overhead gaseous stream and
bottoms liquid stream;
[0111] expanding a portion of the overhead gaseous stream from the
gas/liquid cold separator and then introducing the expanded portion
of the overhead gaseous stream into an upper region of a
demethanizer column;
[0112] expanding a portion of the bottoms liquid stream from the
gas/liquid cold separator and introducing this expanded portion of
the bottoms liquid stream into an intermediate region of the
demethanizer;
[0113] combining another portion of the bottoms liquid stream from
the gas/liquid cold separator with another portion of the overhead
gaseous stream from the gas/liquid cold separator, cooling the
resultant combined cold separator stream by indirect heat exchange
(e.g., in a subcooler) with overhead vapor from the demethanizer,
expanding the cooled resultant combined cold separator stream, and
then introducing the expanded cooled combined cold separator stream
into the top of the demethanizer;
[0114] removing a liquid product stream from the bottom of the
demethanizer and introducing the liquid product stream into the
main heat exchanger where it undergoes indirect heat exchanger with
the first partial stream of the feed stream;
[0115] removing a overhead gaseous stream from the top of the
demethanizer, and subjecting this overhead gaseous stream to
indirect heat exchange (e.g., in a subcooler) with the combined
cold separator streams, whereby the combined cold separator streams
is cooled and partially condensed and the overhead gaseous stream
from the top of the demethanizer is heated, further heating the
overhead gaseous stream from the top of the demethanizer by
indirect heat exchange with the second partial feed stream, and
then compressing and removing at least a portion of the overhead
gaseous stream from the demethanizer as residue gas (another
optional portion can be removed as fuel gas);
[0116] introducing at least a portion of the residue gas stream
from the overhead gaseous stream of the demethanizer into the main
heat exchanger wherein the residue gas stream is cooled by indirect
heat exchange, and then subjecting the cooled residue gas stream to
further indirect heat exchange (e.g., in the subcooler) with the
overhead gaseous stream from the top of the demethanizer whereby
the residue gas stream is further cooled;
[0117] expanding a first portion of the further cooled residue gas
stream and introducing the resultant partially liquefied first
portion of the residue gas stream into an upper region of the
demethanizer; and
[0118] introducing a second portion of the further cooled residue
gas stream into a further separation means (e.g., a further
gas/liquid separator (LNGL separator, i.e., a separator that
integrates and combines the NGL and LNG units)) or a further
distillation column), recovering an overhead residue gas stream
from said further separation means, recovering a liquid stream from
the further separation means, and feeding this liquid stream from
the further separation means to an LNG exchanger, where
liquefaction is performed.
[0119] In accordance with a fifth process aspect of the invention,
there is provided a further process comprising:
[0120] splitting a feed stream containing light hydrocarbons (e.g.,
a natural gas feed stream) into at least a first partial stream and
a second partial stream;
[0121] introducing the first partial stream of the feed stream into
a main heat exchanger (e.g., a plate-fin heat exchanger or shell
and tube heat exchanger) wherein the first partial stream of the
feed stream is cooled and partially condensed by indirect heat
exchange;
[0122] introducing the second partial stream of the feed stream
into a heat exchanger wherein the second partial stream of the feed
stream is cooled and partially condensed by indirect heat
exchange;
[0123] recombining the first and second partial streams of the feed
stream, and optionally subjecting the resultant recombined feed
stream to heat exchange with a refrigerant (e.g., a propane
refrigerant);
[0124] introducing the cooled recombined feed stream into a
gas/liquid cold separator to produce an overhead gaseous stream and
bottoms liquid stream;
[0125] expanding a portion of the overhead gaseous stream from the
gas/liquid cold separator and then introducing the expanded portion
of the overhead gaseous stream into an upper region of a
demethanizer column;
[0126] expanding a portion of the bottoms liquid stream from the
gas/liquid cold separator and introducing this expanded portion of
the bottoms liquid stream into an intermediate region of the
demethanizer;
[0127] combining another portion of the bottoms liquid stream from
the gas/liquid cold separator with another portion of the overhead
gaseous stream from the gas/liquid cold separator, cooling the
resultant combined cold separator stream by indirect heat exchange
(e.g., in a subcooler) with overhead vapor from the demethanizer,
expanding the cooled resultant combined cold separator stream, and
then introducing the expanded cooled combined cold separator stream
into the top of the demethanizer;
[0128] removing a liquid product stream from the bottom of the
demethanizer and introducing the liquid product stream into the
main heat exchanger where it undergoes indirect heat exchanger with
the first partial stream of the feed stream;
[0129] removing a first portion of an overhead gaseous stream from
the top of the demethanizer, and subjecting this first portion of
the overhead gaseous stream to indirect heat exchange (e.g., in a
subcooler) with the combined cold separator stream, whereby the
combined cold separator stream is cooled and partially condensed
and the overhead gaseous stream from the top of the demethanizer is
heated, further heating the overhead gaseous stream from the top of
the demethanizer by indirect heat exchange with the second partial
feed stream, and then compressing and removing at least a portion
of the overhead gaseous stream from the demethanizer as residue gas
(another optional portion can be removed as fuel gas);
[0130] removing a second portion of the overhead gaseous from the
demethanizer as a side stream, and subjecting the side stream to
indirect heat exchange with a refrigerant fluid whereby the side
stream is further cooled and partially liquefied:
[0131] introducing the partially liquefied side stream into a
further separation means (e.g., a further gas/liquid separator or a
further distillation column), recovering a liquid stream
(containing ethane and heavier hydrocarbon components, of the
partially liquefied side stream) and introducing the recovered
liquid stream into the demethanizer as a liquid reflux stream,
and
[0132] recovering an overhead vapor stream rich in methane, from
the further separation means, subjecting the overhead vapor stream
to indirect heat exchange with a refrigerant fluid for additional
cooling and partial condensation, and feeding the resultant
condensate to an LNG exchanger, where liquefaction is
performed.
[0133] In accordance with a sixth process aspect of the invention,
there is provided a further process comprising:
[0134] splitting a feed stream containing light hydrocarbons (e.g.,
a natural gas feed stream) into at least a first partial stream and
a second partial stream;
[0135] introducing the first partial stream of the feed stream into
a main heat exchanger (e.g., a plate-fin heat exchanger or shell
and tube heat exchanger) wherein the first partial stream of the
feed stream is cooled and partially condensed by indirect heat
exchange;
[0136] introducing the second partial stream of the feed stream
into a heat exchanger wherein the second partial stream of the feed
stream is cooled and partially condensed by indirect heat
exchange;
[0137] recombining the first and second partial streams of the feed
stream, and optionally subjecting the resultant recombined feed
stream to heat exchange with a refrigerant (e.g., a propane
refrigerant);
[0138] introducing the cooled recombined feed stream into a
gas/liquid cold separator to produce an overhead gaseous stream and
bottoms liquid stream;
[0139] expanding a portion of the overhead gaseous stream from the
gas/liquid cold separator and then introducing the expanded portion
of the overhead gaseous stream into an upper region of a
demethanizer column;
[0140] expanding a portion of the bottoms liquid stream from the
gas/liquid cold separator and introducing this expanded portion of
the bottoms liquid stream into an intermediate region of the
demethanizer;
[0141] combining another portion of the bottoms liquid stream from
the gas/liquid cold separator with another portion of the overhead
gaseous stream from the gas/liquid cold separator, cooling the
resultant combined cold separator stream by indirect heat exchange
(e.g., in a subcooler) with overhead vapor from the demethanizer,
expanding the cooled resultant combined cold separator stream, and
then introducing the expanded cooled combined cold separator stream
into the top of the demethanizer;
[0142] removing a liquid product stream from the bottom of the
demethanizer and introducing the liquid product stream into the
main heat exchanger where it undergoes indirect heat exchanger with
the first partial stream of the feed stream;
[0143] removing a overhead gaseous stream from the top of the
demethanizer, and subjecting this overhead gaseous stream to
indirect heat exchange (e.g., in a subcooler) with the combined
cold separator stream, whereby the combined cold separator stream
is cooled and partially condensed and the overhead gaseous stream
from the top of the demethanizer is heated, further heating the
overhead gaseous stream from the top of the demethanizer by
indirect heat exchange with the second partial feed stream;
[0144] recycling at least a portion of overhead gaseous stream from
the top of the demethanizer, after indirect heat exchange with the
second partial feed stream, as a residue gas stream to a heat
exchanger wherein the residue gas stream is cooled and partially
condensed by indirect heat exchange (e.g., with a refrigerant), and
then introducing the cooled and partially condensed residue gas
stream into a further separation means (e.g., a further gas/liquid
separator or a further distillation column), recovering a residue
liquid stream from the further separation means and introducing the
residue liquid stream into the top region of the demethanizer as
reflux; and
[0145] recovering an overhead gas stream from the further
separation means, cooling the overhead gas stream by indirect heat
exchange (e.g., with a refrigerant), expanding the further cooled
overhead gas stream and introducing this expanded further cooled
overhead gas stream into a second further separation means (e.g., a
further gas/liquid separator (LNGL separator) or a further
distillation column), recovering an overhead stream from the second
further separation means as a further residue gas (boil off gas),
recovering a liquid stream from the second further separation
means, and feeding this liquid stream from the second further
separation means to an LNG exchanger, where liquefaction is
performed.
[0146] In accordance with a seventh process aspect of the
invention, there is provided a further process comprising:
[0147] splitting a feed stream containing light hydrocarbons (e.g.,
a natural gas feed stream) into at least a first partial stream and
a second partial stream;
[0148] introducing the first partial stream of the feed stream into
a main heat exchanger (e.g., a plate-fin heat exchanger or shell
and tube heat exchanger) wherein the first partial stream of the
feed stream is cooled and partially condensed by indirect heat
exchange;
[0149] introducing the second partial stream of the feed stream
into a heat exchanger wherein the second partial stream of the feed
stream is cooled and partially condensed by indirect heat
exchange;
[0150] recombining the first and second partial streams of the feed
stream, and optionally subjecting the resultant recombined feed
stream to heat exchange with a refrigerant (e.g., a propane
refrigerant);
[0151] introducing the cooled recombined feed stream into a
gas/liquid cold separator to produce an overhead gaseous stream and
bottoms liquid stream;
[0152] expanding a portion of the overhead gaseous stream from the
gas/liquid cold separator and then introducing the expanded portion
of the overhead gaseous stream into an upper region of a
demethanizer column;
[0153] expanding a portion of the bottoms liquid stream from the
gas/liquid cold separator and introducing this expanded portion of
the bottoms liquid stream into an intermediate region of the
demethanizer;
[0154] combining another portion of the bottoms liquid stream from
the gas/liquid cold separator with another portion of the overhead
gaseous stream from the gas/liquid cold separator, cooling the
resultant combined cold separator stream by indirect heat exchange
in a heat exchanger (e.g. a subcooler) with overhead vapor from the
demethanizer, expanding the cooled resultant combined cold
separator stream, and then introducing the expanded cooled combined
cold separator stream into the top of the demethanizer;
[0155] removing a liquid product stream from the bottom of the
demethanizer and introducing the liquid product stream into the
main heat exchanger where it undergoes indirect heat exchanger with
the first partial stream of the feed stream;
[0156] removing a overhead gaseous stream from the top of the
demethanizer, and subjecting this overhead gaseous stream to
indirect heat exchange in with the combined cold separator stream
(e.g., in the subcooler), whereby the combined cold separator
stream is cooled and partially condensed and the overhead gaseous
stream from the top of the demethanizer is heated, further heating
the overhead gaseous stream from the top of the demethanizer by
indirect heat exchange with the second partial feed stream, and
then compressing and removing at least a portion of the overhead
gaseous stream from the demethanizer as residue gas (another
optional portion can be removed as fuel gas);
[0157] subjecting at least a portion of the residue gas stream from
the overhead gaseous stream of the demethanizer to heat exchange
(e.g., in the subcooler) wherein the residue gas stream is cooled
by indirect heat exchange with the overhead gaseous stream from the
top of the demethanizer ;
[0158] expanding a portion of the cooled residue gas stream and
introducing the resultant expanded portion of the cooled residue
gas stream into an upper region of the demethanizer, expanding
another portion of the residue gas stream and introducing the
resultant expanded another portion into a further separation means
(e.g., a further gas/liquid separator (LNGL separator) or a further
distillation column), recovering an overhead residue gas stream
from the further separation means as a further residue gas (boil
off gas), recovering a liquid stream from the further separation
means, and feeding this liquid stream from the further separation
means to an LNG exchanger where liquefaction is performed.
[0159] In accordance with a eighth process aspect of the invention,
there is provided a further process comprising:
[0160] splitting a feed stream containing light hydrocarbons (e.g.,
a natural gas feed stream) into at least a first partial stream and
a second partial stream;
[0161] introducing the first partial stream of the feed stream into
a main heat exchanger (e.g., a plate-fin heat exchanger or shell
and tube heat exchanger) wherein the first partial stream of the
feed stream is cooled and partially condensed by indirect heat
exchange;
[0162] introducing the second partial stream of the feed stream
into a heat exchanger wherein the second partial stream of the feed
stream is cooled and possibly partially condensed (depending upon
the composition of the feed gas stream) by indirect heat
exchange;
[0163] recombining the first and second partial streams of the feed
stream, and optionally subjecting the resultant recombined feed
stream to heat exchange with a refrigerant (e.g., a propane
refrigerant);
[0164] introducing the cooled recombined feed stream into a
gas/liquid cold separator to produce an overhead gaseous stream and
bottoms liquid stream;
[0165] expanding a portion of the overhead gaseous stream from the
gas/liquid cold separator and then introducing the expanded portion
of the overhead gaseous stream into an upper region of a
demethanizer column;
[0166] expanding a portion of the bottoms liquid stream from the
gas/liquid cold separator and introducing this expanded portion of
the bottoms liquid stream into an intermediate region of the
demethanizer;
[0167] combining another portion of the bottoms liquid stream from
the gas/liquid cold separator with another portion of the overhead
gaseous stream from the gas/liquid cold separator, cooling the
resultant combined cold separator stream by indirect heat exchange
in a heat exchanger (e.g., a subcooler) with overhead vapor from
the demethanizer, expanding the cooled resultant combined cold
separator stream, and then introducing the expanded cooled combined
cold separator stream into the top of the demethanizer;
[0168] removing a liquid product stream from the bottom of the
demethanizer and introducing the liquid product stream into the
main heat exchanger where it undergoes indirect heat exchanger with
the first partial stream of the feed stream;
[0169] removing a overhead gaseous stream from the top of the
demethanizer, and subjecting this overhead gaseous stream to
indirect heat exchange with the combined cold separator stream
expanding the cooled resultant combined cold separator stream,
whereby the combined cold separator stream is cooled and partially
condensed (depending upon the composition of the stream) and the
overhead gaseous stream from the top of the demethanizer is heated,
further heating the overhead gaseous stream from the top of the
demethanizer by indirect heat exchange with the second partial feed
stream, and then compressing and removing at least a portion of the
overhead gaseous stream from the demethanizer as residue gas
(another optional portion can be removed as fuel gas);
[0170] subjecting at least a portion of the residue gas stream from
the overhead gaseous stream of the demethanizer to heat exchange
(e.g., in the subcooler) wherein the residue gas stream is cooled
by indirect heat exchange with the overhead gaseous stream from the
top of the demethanizer;
[0171] separating the cooled residue gas stream into a first
portion and a second portion, expanding the first portion of the
cooled residue gas stream and introducing the resultant expanded
first portion of the cooled residue gas stream into an upper region
of the demethanizer,
[0172] further cooling and partially condensing the second portion
of the cooled residue gas stream by indirect heat exchange in a
heat exchanger (e.g., against a refrigerant), and then introducing
the cooled and partially condensed second portion of the residue
gas stream into a further separation means (e.g., a further
gas/liquid separator or a further distillation column), recovering
a residue liquid stream from the further separation means and
introducing the residue liquid stream into the top region of the
demethanizer as reflux; and
[0173] recovering an overhead gas stream from the further
separation means, cooling the overhead gas stream by indirect heat
exchange (e.g., with a refrigerant), expanding the further cooled
overhead residue gas stream and introducing this expanded further
cooled overhead residue gas stream into a second further separation
means (e.g., a further gas/liquid separator (LNGL separator) or a
further distillation column), recovering an overhead stream from
the second further separation means as a further residue gas (boil
off gas), recovering a liquid stream from the second further
separation means, and feeding this liquid stream from the second
further separation means to an LNG exchanger, where liquefaction is
performed.
[0174] In accordance with a ninth process aspect of the invention,
there is provided a further process comprising:
[0175] splitting a feed stream containing light hydrocarbons (e.g.,
a natural gas feed stream) into at least a first partial stream and
a second partial stream;
[0176] introducing the first partial stream of the feed stream into
a main heat exchanger (e.g., a plate-fin heat exchanger or shell
and tube heat exchanger) wherein the first partial stream of the
feed stream is cooled and partially condensed by indirect heat
exchange;
[0177] introducing the second partial stream of the feed stream
into a heat exchanger wherein the second partial stream of the feed
stream is cooled and partially condensed by indirect heat
exchange;
[0178] recombining the first and second partial streams of the feed
stream, and optionally subjecting the resultant recombined feed
stream to heat exchange with a refrigerant (e.g., a propane
refrigerant);
[0179] introducing the cooled recombined feed stream into a
gas/liquid cold separator to produce an overhead gaseous stream and
bottoms liquid stream;
[0180] expanding a portion of the overhead gaseous stream from the
gas/liquid cold separator and then introducing the expanded portion
of the overhead gaseous stream into an upper region of a
demethanizer column;
[0181] expanding a portion of the bottoms liquid stream from the
gas/liquid cold separator and introducing this expanded portion of
the bottoms liquid stream into an intermediate region of the
demethanizer;
[0182] combining another portion of the bottoms liquid stream from
the gas/liquid cold separator with another portion of the overhead
gaseous stream from the gas/liquid cold separator, cooling the
resultant combined cold separator stream by indirect heat exchange
in a heat exchanger (e.g., a subcooler) with overhead vapor from
the demethanizer, expanding the cooled resultant combined cold
separator stream, and then introducing the expanded cooled combined
cold separator stream into the top of the demethanizer;
[0183] removing a liquid product stream from the bottom of the
demethanizer and introducing the liquid product stream into the
main heat exchanger where it undergoes indirect heat exchanger with
the first partial stream of the feed stream;
[0184] removing a overhead gaseous stream from the top of the
demethanizer, and subjecting this overhead gaseous stream to
indirect heat exchange with the combined cold separator stream,
(e.g., in the subcooler) whereby the combined cold separator stream
is cooled and partially condensed (depending upon the composition
of the stream) and the overhead gaseous stream from the top of the
demethanizer is heated, further heating the overhead gaseous stream
from the top of the demethanizer by indirect heat exchange with the
second partial feed stream, and then compressing and removing at
least a portion of the overhead gaseous stream from the
demethanizer as a residue gas stream (another optional portion can
be removed as fuel gas);
[0185] cooling a portion of the residue gas stream by indirect heat
exchange in a heat exchanger (e.g., against a refrigerant), and
then introducing the cooled portion of the residue gas stream into
a further separation means (e.g., a further gas/liquid separator or
a further distillation column), recovering a residue liquid stream
from the further separation means and introducing the residue
liquid stream into the top region of the demethanizer as reflux;
and
[0186] recovering an overhead gas stream from the further
separation means, cooling the overhead gas stream by indirect heat
exchange (e.g., with a refrigerant), expanding the further cooled
overhead residue gas stream and introducing this expanded further
cooled overhead gas stream into a second further separation means
(e.g., a further gas/liquid separator (LNGL separator) or a further
distillation column), recovering an overhead stream from the second
further separation means as a further residue gas (boil off gas),
recovering a liquid stream from the second further separation
means, and feeding this liquid stream from the second further
separation means to an LNG exchanger, where liquefaction is
performed.
[0187] According to a general apparatus aspect of the invention
there is provided an apparatus comprising:
[0188] one or more heat exchangers for cooling and partially
condensing by indirect heat exchange a feed stream containing light
hydrocarbons (e.g., a natural gas feed stream);
[0189] gas/liquid cold separator and means (e.g., piping conduits)
for introducing a partially condensed feed stream from the one or
more heat exchangers into the gas/liquid cold separator, the
gas/liquid cold separator having upper outlet means (e.g., piping
conduits) for removing an overhead gaseous stream and lower outlet
means (e.g., piping conduits) for removing a bottoms liquid
stream;
[0190] means for introducing overhead gaseous stream and bottoms
liquid stream from the gas/liquid cold separator into a
fractionation system comprising (a) a light ends fractionation
column and a heavy ends fractionation column, or (b) a demethanizer
(or deethanizer) column, the means comprising an expansion device
for expanding at least a portion of overhead gaseous stream from
the gas/liquid cold separator and means (e.g., piping conduits) for
introducing expanded overhead gaseous stream into (a) a lower
region of a light ends fractionation column or (b) an upper region
of a demethanizer (or deethanizer) column, and means (e.g., piping
conduits) for introducing at least a portion of bottoms liquid
stream from the gas/liquid cold separator into (a) a heavy ends
fractionation column at an intermediate point thereof or (b) a
demethanizer (or deethanizer) column at an intermediate point
thereof;
[0191] means (e.g., piping conduits) for removing a liquid product
stream from the bottom of (a) the heavy ends fractionation column
or (b) the demethanizer (or deethanizer) column;
[0192] means (e.g., piping conduits) for removing a overhead
gaseous stream from the top of (a) the light ends fractionation
column or (b) the demethanizer (or deethanizer) column, and
[0193] if the fractionation system comprises a light ends
fractionation column and a heavy ends fractionation column, the
apparatus further comprises means (e.g., piping conduits) for
removing a bottoms liquid stream from a lower region of the light
ends fractionation column, and introducing this bottoms liquid
stream from the light ends fractionation column into the upper
region of the heavy ends fractionation column;
said apparatus further comprising:
[0194] (a) when the fractionation system comprises a light ends
fractionation column and a heavy ends fractionation column, [0195]
(i) a heat exchanger for subjecting a first portion of the light
ends fractionation column overhead gaseous stream to indirect heat
exchange (e.g., a subcooler) with an overhead gaseous stream
removed from the top of the heavy ends fractionation column,
whereby the overhead gaseous stream from the top of the heavy ends
fractionation column is cooled and partially condensed, and means
(e.g., piping conduits) for introducing this cooled and partially
condensed overhead gaseous stream from the top of the heavy ends
fractionation column into the light ends fractionation column;
[0196] (ii) means (e.g., piping conduits) for removing a second
portion of the overhead gaseous stream from the light ends
fractionation column as a side stream, and a further heat exchanger
for subjecting the side stream to indirect heat exchange to further
cool, and partially liquefy the side stream; [0197] (iii) means
(e.g., piping conduits) for introducing the partially liquefied
side stream into a further separation means, means (e.g., piping
conduits) for recovering liquid product from the further separation
means and means (e.g., piping conduits) for introducing the
recovered liquid product into the light ends fractionation column
as a liquid reflux stream and/or the heavy ends fractionation
column as a liquid reflux stream, [0198] (iv) means (e.g., piping
conduits) for recovering an overhead vapor stream from the further
separation means, a further heat exchanger for subjecting this
overhead vapor stream to indirect heat exchange for additional
cooling and partial condensation, means (e.g., piping conduits) for
feeding the resultant vapor and condensate to an LNG separator, and
means (e.g., piping conduits) for recovering LNG liquid product
from the LNG separator, and [0199] (v) means (e.g., piping
conduits) for recovering an overhead vapor stream from the further
separation means, a compressor for compressing this overhead vapor
stream to form a residue gas; or
[0200] (b) when the fractionation system comprises a light ends
fractionation column and a heavy ends fractionation column, [0201]
(i) a heat exchanger for subjecting the light ends fractionation
column overhead gaseous stream to indirect heat exchange (e.g., in
a subcooler) with an overhead gaseous stream removed from the top
of the heavy ends fractionation column, whereby the overhead
gaseous stream from the light ends fractionation column Is heated
and the overhead gaseous stream from the top of the heavy ends
fractionation column is cooled and partially condensed, and means
(e.g., piping conduits) for introducing this cooled and partially
condensed overhead gaseous stream from the top of the heavy ends
fractionation column into the light ends fractionation column;
[0202] (ii) means (e.g., piping conduits) for introducing the
overhead gaseous stream from the light ends fractionation column to
a heat exchanger for further heating, and a compressor for
compressing the overhead gaseous stream from the light ends
fractionation column to produce a residue gas; [0203] (iii) a
further heat exchanger for further cooling at least a portion of
the residue gas whereby the portion of the residue gas is partially
liquefied; [0204] (iv) means (e.g., piping conduits) for
introducing a portion of the partially liquefied residue gas into
the light ends fractionation column; [0205] (v) an expansion device
for expanding another portion of the partially liquefied residue
gas and means (e.g., piping conduits) for introducing this expanded
portion into a further separation means; [0206] (vi) means (e.g.,
piping conduits) for recovering liquid product from the further
separation means; and [0207] (vii) means (e.g., piping conduits)
for recovering an overhead vapor stream from the further separation
means, a compressor for compressing this overhead vapor stream to
form a residue gas; or
[0208] (c) when the fractionation system comprises a demethanizer
(or deethanizer) column, [0209] (j) a heat exchanger for subjecting
a first portion of the overhead gaseous stream from the
demethanizer (or deethanizer) column to indirect heat exchange
(e.g., in a subcooler) with a stream obtained by combining a
portion of the overhead gaseous stream from the gas/liquid cold
separator and a portion of the bottoms liquid stream from
gas/liquid cold separator to obtain a residue gas; [0210] (ii)
means (e.g., piping conduits) for removing a second portion of the
overhead gaseous from the demethanizer (or deethanizer) column as a
side stream, and a further heat exchanger for partially liquefying
the side stream by heat exchange; [0211] (iii) means (e.g., piping
conduits) for introducing the partially liquefied side stream into
a further separation means, means (e.g., piping conduits) for
recovering liquid product from the further separation means and
introducing the recovered liquid product into the demethanizer (or
deethanizer) column as a liquid reflux stream, and [0212] (iv)
means (e.g., piping conduits) for recovering an overhead vapor
stream from the further separation means, a further heat exchange
means for subjecting this overhead vapor stream to indirect heat
exchange for additional cooling and partial condensation, and means
(e.g., piping conduits) for removing the resultant condensate as a
final LNG liquid product; or
[0213] (d) when the fractionation system comprises a demethanizer
(or deethanizer) column, [0214] (i) a heat exchanger for subjecting
the demethanizer (or deethanizer) column overhead gaseous stream to
indirect heat exchange (e.g., in a subcooler) with a stream
obtained by combining a portion of the overhead gaseous stream from
the gas/liquid cold separator and a portion of the bottoms liquid
stream from gas/liquid cold separator; [0215] (ii) means for
subjecting the overhead gaseous stream from the demethanizer (or
deethanizer) column to further heating and a compressor for
compressing the overhead gaseous stream from the demethanizer (or
deethanizer) column to produce a residue gas; [0216] (iii) a
further heat exchanger for cooling at least a portion of the
residue gas whereby the portion of the residue gas is partially
liquefied; [0217] (iv) means (e.g., piping conduits) for
introducing this partially liquefied residue gas into a further
separation means; [0218] (v) means (e.g., piping conduits) for
recovering liquid product from the further separation means and
introducing the recovered liquid product as reflux to the
demethanizer (or deethanizer) column; [0219] (vi) means (e.g.,
piping conduits) for recovering an overhead vapor stream from the
further separation means, means for subjecting this overhead vapor
stream to heat exchange whereby the overhead vapor stream is
partially liquefied; [0220] (vii) means (e.g., piping conduits) for
introducing this partially liquefied overhead vapor stream into
another further separation means; and [0221] (viii) means (e.g.,
piping conduits) for recovering LNG liquid product from the another
further separation means.
[0222] In accordance with a first apparatus aspect of the
invention, there is provided an apparatus for performing the first
aspect of the inventive process. The apparatus comprises:
[0223] a light ends fractionation column and a heavy ends
fractionation column;
[0224] a main heat exchanger (e.g., a plate-fin heat exchanger or
shell and tube heat exchanger) for cooling and partially condensing
a natural gas feed stream by indirect heat exchange;
[0225] a gas/liquid cold separator for separating a partially
condensed feed stream into an overhead gaseous stream and bottoms
liquid stream;
[0226] an expansion device (e.g., expansion valve, turbo-expander)
for expanding overhead gaseous stream from the gas/liquid cold
separator and means for introducing (e.g., pipes, conduits)
expanded overhead gaseous stream into a lower region of the light
ends fractionation column;
[0227] means for introducing (e.g., pipes, conduits) bottoms liquid
stream from the gas/liquid cold separator into the heavy ends
fractionation column at an intermediate point thereof;
[0228] means for removing (e.g., pipes, conduits) a liquid product
stream from the bottom of the heavy ends fractionation column and
means for introducing (e.g., pipes, conduits) liquid product stream
from the bottom of the heavy ends fractionation column into the
main heat exchanger for indirect heat exchange with natural gas
feed stream;
[0229] means for removing (e.g., pipes, conduits, pump) bottoms
liquid stream from a lower region of the light ends fractionation
column and introducing it into the upper region of the heavy ends
fractionation column;
[0230] means for removing (e.g., pipes, conduits) overhead gaseous
stream from the top of the light ends fractionation column and
introducing overhead gaseous stream from the top of the light ends
fractionation column into a subcooler for indirect heat exchange
with overhead gaseous stream removed from the top of the heavy ends
fractionation column;
[0231] means for removing (e.g., pipes, conduits) bottoms liquid
stream from a lower region of the heavy ends fractionation column,
a heat exchanger for heating bottoms liquid stream from a lower
region of the heavy ends fractionation column by indirect heat
exchange, and means for returning (e.g., pipes, conduits) bottoms
liquid stream to the lower region of the heavy ends fractionation
column as a reboiler stream;
[0232] means for removing (e.g., pipes, conduits) overhead gaseous
stream from the top of the heavy ends fractionation column and
introducing it into the subcooler for indirect heat exchange with
overhead gaseous stream from the top of the light ends
fractionation column;
[0233] means for removing (e.g., pipes, conduits) cooled and
partially condensed overhead gaseous stream from the subcooler and
introducing it into the light ends fractionation column;
[0234] means for removing (e.g., pipes, conduits) a portion of the
overhead gaseous from the light ends fractionation column as a side
stream, a flow-control valve for partially liquefying the side
stream, and a refrigerant heat exchanger for subjecting partially
liquefied side stream to indirect heat exchange with a refrigerant
fluid for further cooling;
[0235] means for introducing (e.g., pipes, conduits) partially
liquefied side stream into a further separation means (e.g., a
further gas/liquid separator or a further distillation column),
[0236] means for recovering (e.g., pipes, conduits) liquid product
from the further separation means and introducing it into the light
ends fractionation column as a liquid reflux stream and/or the
heavy ends fractionation column as a liquid reflux stream, and
[0237] means for recovering (e.g., pipes, conduits) an overhead
vapor stream from the further separation means,
[0238] a heat exchanger for subjecting overhead vapor stream from
the further separation means to indirect heat exchange with a
refrigerant fluid for additional cooling and partial condensation,
and
[0239] means for feeding (e.g., pipes, conduits) resultant
condensate to an LNG exchanger, where liquefaction is
performed.
[0240] Second through ninth apparatus aspects of the invention are
apparatus systems capable of performing the processes corresponding
to each of the second to ninth process aspects described above,
examples of which are illustrated in the Figures.
DESCRIPTION OF THE DRAWINGS
[0241] The invention as well as further advantages, features and
examples of the present invention are explained in more detail by
the following descriptions of embodiments based on the Figures,
wherein:
[0242] FIGS. 1-27 each schematically show shows exemplary
embodiments in accordance with the invention.
[0243] The embodiments of FIGS. 1-16 are modifications of the
CRYO-PLUS.TM. process. The embodiments of FIGS. 17-21, on the other
hand, are modifications of the so-called Gas Subcooled Process
(GSP), and the embodiments of FIGS. 22-26 are modifications of the
so-called Recycle Split Vapor (RSV) process.
[0244] In FIG. 1, gas feed stream (1), containing, for example,
helium, nitrogen methane, ethane, ethylene, and C3+ hydrocarbons
(e.g., a natural gas feed stream) is introduced into the system at
a temperature of, e.g., 10 to 50.degree. C. and a pressure of,
e.g., 250 to 1400 psig. The gas feed stream (1) is cooled and
partially condensed by indirect heat exchange in a main heat
exchanger (2) against process streams (15, 16, 18) and then
introduced into a gas/liquid cold separator (3). The gaseous
overhead stream (4) removed from the top of the cold separator (3)
is expanded, for example, in a turboexpander (5), and then
introduced (6) into the lower region of the light ends
fractionation column (7) (LEFC). The bottoms liquid stream (8) from
the cold separator (3) is introduced into the heavy ends
fractionation column (9) (HEFC) at an intermediate point thereof.
The light ends fractionation column typically operates at a
temperature of -70 to -135.degree. C. and a pressure of 60 to 500
psig. The heavy ends fractionation column typically operates at a
temperature of -135 to +70.degree. C. and a pressure of 60 to 500
psig.
[0245] A liquid stream (10) is removed from the bottom of the LEFC
(7) and delivered, via pump (11), to the top of the HEFC (9). An
overhead vapor product (12), also called a residue gas, is removed
from the top of the LEFC (7), undergoes indirect heat exchange in a
subcooler (13) with a gas stream (14) discharged from the top of
the HEFC (9), before being heated in the main heat exchanger (2)
and then discharged from the system. A portion of this overhead
vapor product can be used as fuel gas. Another portion of the
overhead vapor product can be further compressed before being sent
to a gas pipeline.
[0246] In a typical system, the warm overhead product from the LEFC
can be sent to a gas pipeline for delivery to the consumer, or it
can be 100% liquefied in an LNG unit, or a portion can flow to the
gas pipeline while the remainder can be liquefied by the LNG unit.
Liquefying the overhead gas product after warming the gas requires
energy. However, as described further below, the inventive process
uses overhead gas product from the top of the LEFC as the LNG unit
feed, thereby preserving cooling of the overhead gas product and
reducing energy consumption.
[0247] A liquid product stream (15) is removed from the bottom of
the HEFC (9) and passed through the main heat exchanger (2) where
it undergoes indirect heat exchanger with the gas feed stream (1).
In addition, a further liquid stream (16) is removed from a first
intermediate point of the HEFC (9). This further liquid stream (16)
is heated by indirect heat exchange with the gas feed stream (1)
(e.g., in main heat exchanger (2)), and then reintroduced (17) into
the HEFC (9) at a second intermediate point below the first
intermediate point. An additional liquid stream (18) is removed
from the lower region of the HEFC (9), heated in an indirect heat
exchanger (e.g., in main heat exchanger (2) acting as a reboiler
for the HEFC (9), and returned (19) to the lower region of the HEFC
(9). Further, as noted above, a gas stream (14) is removed from the
top of the HEFC (9).
[0248] Additional structural elements shown in FIG. 1 are a product
surge tank (20) which allows for recycling of a portion of the
liquid product stream (15) back to the bottom of the HEFC (9).
There also can be a trim reboiler (21) in the reboiler system of
the HEFC (9) to supplement the heating provided by the reboiler for
the HEFC. Also, in addition to the cooling provided in the main
heat exchanger, the refrigeration needed for the cooling and
partially condensation of the gas feed stream (1) can be partially
provided by passing the gas feed stream (1) through a chiller (22),
wherein it undergoes indirect heat exchange with an external
refrigerant stream.
[0249] In accordance with the invention, a side stream (23) is
taken from the overhead vapor product of the LEFC and partially
liquefied, via Joule-Thomson effect cooling, across a flow-control
valve (24). The partially liquefied vapor stream is then delivered
to a refrigerant system wherein it undergoes indirect heat exchange
with a refrigerant fluid for further cooling. The resultant stream
(25) is then fed into a further separation means (26), such as a
further gas/liquid separator or a further distillation column,
where the majority of ethane as well as heavier hydrocarbon
components are recovered as liquid product (27) and returned to the
LEFC as a liquid reflux stream. If a further distillation column is
desired as the separation means, it can be integrated into the LNG
unit. If the further distillation column requires a reboiler, the
reboiler can be integrated into the LNG exchanger.
[0250] The overhead vapor stream (28) from the further separation
means, rich in methane, undergoes indirect heat exchange with the
refrigerant fluid of the refrigerant system for additional cooling.
The resultant cooled stream (29) is then fed into the LNG exchanger
where it is subjected to liquefaction to form the LNG product. This
cooled stream (29) can then be sent to a gas/liquid separator for
separating light components, such as nitrogen, before being
introduced into the LNG unit.
[0251] At an intermediate point in the LNG exchanger, a
vapor-liquid stream can be removed and introduced into an
intermediate separator to separate heavier hydrocarbons (C.sub.2+)
and return a lighter (essentially nitrogen, methane and ethane)
stream to the LNG exchanger for final liquefaction, to allow the
LNG product to meet desired specifications. The resulting liquids
are increased in pressure via a pump and can be introduced into the
LEFC as an additional reflux stream to further improve the C.sub.2+
recovery. The vapor stream from the intermediate separator reenters
the LNG exchanger and proceeds, via additional cooling, to
liquefy.
[0252] This integration of the NGL and LNG processes allows for a
significant reduction of energy consumption in the LNG unit without
compromising the NGL recovery process. The utilization of a portion
of the cold overhead vapor from the LEFC of the NGL process reduces
refrigeration requirements, allowing the processes to take place in
a more efficient manner that not only reduces overall energy
consumption, but also provides improved recoveries for both
processes.
[0253] FIG. 2 illustrates an alternative embodiment of the
invention. As in FIG. 1, a side stream (23) is taken from the
overhead vapor product (12) of the LEFC and partially liquefied
across a flow-control valve (24). The partially liquefied vapor
undergoes indirect heat exchange with a refrigerant fluid for
further cooling and is then fed into a further separation means
(e.g., a further gas/liquid separator or further distillation
column) where the majority of ethane as well as heavier hydrocarbon
components are recovered as liquid product (27) and returned to the
LEFC (7) as a liquid reflux stream. The methane-rich overhead vapor
stream (28) from the further separation means undergoes indirect
heat exchange with the refrigerant fluid for additional cooling,
and is then fed as into the LNG exchanger, where liquefaction
occurs.
[0254] In FIG. 2, however, additional reflux streams are provided
for the LEFC (7). Prior to expansion of the gaseous overhead stream
(4), obtained from cold separator (3), in the turboexpander (5), a
portion (30) of the gaseous overhead stream (4) is fed to the
subcooler (13) where it undergoes indirect heat exchange with the
overhead vapor from LEFC (7). In the subcooler (13), portion (30)
of the gaseous overhead stream (4) is cooled further and partially
liquefied, and then is introduced into the top region of the LEFC
(7) to thereby provide additional reflux (31).
[0255] In addition, a portion (32) of bottoms liquid stream (8)
from cold separator (3) is delivered to a liquid/liquid heat
exchanger (33), where it undergoes indirect heat exchange with
bottom liquid (10) removed from the bottom of the LEFC (7). The
resultant stream (34) is then fed to an intermediate region of the
LEFC (7) as a liquid reflux. These two additional reflux streams
for the LEFC (7) improve recovery of the ethane and heavier
hydrocarbon components.
[0256] A further embodiment is illustrated in FIG. 3. As in FIGS. 1
and 2, a side stream (23) is taken from the overhead vapor product
(12) of the LEFC and partially liquefied across a flow-control
valve (24). The partially liquefied vapor undergoes indirect heat
exchange with a refrigerant fluid for further cooling and is then
fed into a further separation means (e.g., a further gas/liquid
separator or further distillation column) where the majority of
ethane as well as heavier hydrocarbon components are recovered in
as liquid product (27) and returned to the LEFC (7) as a liquid
reflux stream. The methane-rich overhead vapor stream (28) from the
further separation means undergoes indirect heat exchange with the
refrigerant fluid for additional cooling, and is then fed as into
the LNG exchanger, where liquefaction occurs.
[0257] As in FIG. 2, FIG. 3 provides additional reflux for the LEFC
(7). Here again, prior to expansion in the turboexpander (5), a
portion (30) is branched off from the gaseous overhead stream (4)
removed from the top of cold separator (3) (4). In this case,
however, the portion (30) is combined with a portion (32) of
bottoms liquid stream (8) removed from the bottom of the cold
separator (3). The relative proportions of the liquid and vapor
removed provide the mechanism to allow the generation of additional
reflux in the indirect heat exchanger (subcooler) that follows. For
example, in the combined stream the proportion of the gaseous
overhead stream is up to 80%, and the proportion of the bottoms
liquid stream is up to 99%
[0258] The combined stream (35) is fed to the subcooler (13) where
it undergoes indirect heat exchange with the overhead vapor from
LEFC (7). Stream (35) is cooled and partially liquefied in the
subcooler (13) and introduced into the top region of the LEFC (7)
to provide additional reflux. This additional reflux stream for the
LEFC (7) improves recovery of the ethane and heavier hydrocarbon
components.
[0259] FIG. 4 illustrates a modification of the embodiment of FIG.
3. As in FIGS. 1-3, a side stream (23) is taken from the overhead
vapor product (12) of the LEFC and partially liquefied across a
flow-control valve (24). In FIG. 4, this partially liquefied stream
is treated in the same manner as in As in FIG. 3, a portion (30) of
the gaseous overhead stream (4) removed from the top of cold
separator (3) is combined with a portion (32) of bottoms liquid
stream (8) removed from the bottom of the cold separator (3). The
combined stream (35) is fed to the subcooler (13), where it
undergoes indirect heat exchange with the overhead vapor from LEFC
(7). The cooled and partially liquefied stream (35) is introduced
into the top region of the LEFC (7) to provide additional
reflux.
[0260] As in FIGS. 1-3, a side stream (23) is taken from the
overhead vapor product (12) of the LEFC and partially liquefied
across a flow-control valve (24). However, in FIG. 4, this side
stream (23) taken from the overhead vapor product (12) of the LEFC
is treated differently. The partially liquefied vapor undergoes
indirect heat exchange with a refrigerant fluid for further cooling
and is then fed into a further separation means (e.g., a further
gas/liquid separator or further distillation column). The
methane-rich overhead vapor stream (28) from the further separation
means undergoes indirect heat exchange with the refrigerant fluid
for additional cooling, and is then fed as into the LNG exchanger,
where liquefaction occurs. The majority of ethane as well as
heavier hydrocarbon components are recovered from the bottom of the
further separation means as liquid product (27). But, instead of
being sent to the LEFC (7), this liquid product (27) is introduced
into the top of the HEFC (9) as a liquid reflux stream.
[0261] FIG. 5 illustrates a modification of the embodiment of FIG.
2. As in FIG. 2, a side stream (23) is taken from the overhead
vapor product (12) of the LEFC and partially liquefied across a
flow-control valve (24). The partially liquefied vapor undergoes
indirect heat exchange with a refrigerant fluid for further cooling
and is then fed into a further separation means (26) where the
majority of ethane as well as heavier hydrocarbon components are
recovered as liquid product (27) and returned to the LEFC (7) as a
liquid reflux stream. The methane-rich overhead vapor stream (28)
from the further separation means (26) undergoes indirect heat
exchange with the refrigerant fluid for additional cooling, and is
then fed as into the LNG exchanger, where liquefaction occurs.
[0262] Further, as in FIG. 2, additional reflux streams are
provided for the LEFC (7). Prior to expansion of the gaseous
overhead stream (4), obtained from cold separator (3), in the
turboexpander (5), portion (30) of the gaseous overhead stream (4)
removed from the top of cold separator (3) is fed to the subcooler
(13), where it undergoes indirect heat exchange with the overhead
vapor (12) from LEFC (7). In the subcooler (13), portion (30) of
the gaseous overhead stream (4) is cooled further and partially
liquefied in the subcooler (13) and introduced into the top region
of the LEFC (7) to thereby provide additional reflux. In addition,
a portion (32) of bottoms liquid stream (8) removed from the bottom
of the cold separator (3) is delivered to a liquid/liquid heat
exchanger (33), where it undergoes indirect heat exchange with the
bottom liquid stream (10) removed from the bottom of the LEFC (7).
The resultant stream (34) is then fed to an intermediate region of
the LEFC (7) as a liquid reflux.
[0263] FIG. 5, however, incorporates a refrigeration loop through
the NGL process which results in a reduction in energy consumption.
Specifically, a stream of refrigerant fluid (36) from the
refrigerant system is fed through the main heat exchanger (2)
(e.g., a plate-fin heat exchanger) where it undergoes indirect heat
exchange with the gas feed stream (1), the liquid product stream
(15) from the bottom of the HEFC (9), the further liquid stream
(16) from an intermediate point of the HEFC (9), the reboiler
stream (18) removed from the bottom region of the HEFC (9), and the
overhead vapor product stream (12) removed from the top of the LEFC
(7). The refrigerant stream, cooled and partially liquefied, leaves
the main heat exchanger as stream (37). Thereafter, the refrigerant
stream is introduced into the subcooler (13) where it is further
cooled and liquefied. This stream is then flashed across a valve
(38), causing the fluid to reach even colder temperatures and is
then fed back to the subcooler (13) to provide cooling to the
reflux streams of the LEFC (7). The refrigerant stream (39) then
returns to the main heat exchanger (2), where it serves as a
coolant to the NGL process streams. The refrigerant stream is then
returned to the refrigeration system for compression.
[0264] FIG. 6 illustrates an embodiment which is similar to that
shown in FIG. 5, but with a modified refrigeration loop. A stream
of refrigerant fluid (36) from the refrigerant system is fed
through the main heat exchanger (2) where it undergoes indirect
heat exchange with the gas feed stream (1), the liquid product
stream (15) from the bottom of the HEFC (9), the further liquid
stream (16) from an intermediate point of the HEFC (9), the
reboiler stream (18) removed from the bottom region of the HEFC
(9), and the overhead vapor product stream (12) removed from the
top of the LEFC (7). The refrigerant stream, cooled and partially
liquefied, leaves the main heat exchanger (2) as stream (37).
Thereafter, the refrigerant stream is introduced into the subcooler
(13) where it is further cooled and liquefied. This stream is then
introduced into a heat exchanger (40) for cooling the side stream
(23) from the LEFC overhead vapor product stream (12). The
refrigerant stream exits heat exchanger (40) and is flashed across
a valve (41), causing the fluid to reach even colder temperatures.
The resultant stream is then fed back to the same heat exchanger
(40) to provide further cooling. Thereafter, the refrigerant passes
through the subcooler (13) and the main heat exchanger (2), and
then flows to the refrigeration system for compression.
[0265] FIG. 7 shows a further embodiment of the invention. In this
embodiment, a side stream is not removed from the overhead vapor
product of the LEFC. Moreover, a residual gas stream is utilized in
the main heat exchanger (2) (and the subcooler (13) and then
treated in the further separation means (26). This embodiment
allows for a reduction in utility consumption when compared to a
standalone LNG unit, thereby rendering the process more energy
efficient.
[0266] Thus, in FIG. 7, a portion of the high pressure residue gas
(42) is introduced into the cryogenic process and passes through
the main heat exchanger (2). In main heat exchanger (2), this high
pressure residue gas is cooled by heat exchange against various
process stream (e.g., residue gas from the top of the LEFC, the
feed stream, product stream from the bottom of the HEFC, and side
streams from the HEFC). Thereafter, the cooled high pressure
residue gas (43) is further cooled in the subcooler (13) by heat
exchange with overhead vapor product (12), also called a residue
gas, removed from the top of the LEFC (7), and overhead vapor
product (12) removed from the top of the HEFC (9).
[0267] A portion of the cooled high pressure reside gas stream (44)
is then flashed expanded (e.g., via an expansion valve) to the
operating pressure of the LEFC (7) (and combined with the overhead
vapor product (14) removed from the top of the HEFC, after the
latter is subcooled in subcooler (13). The combined stream serves
as reflux to the LEFC and is considered the top feed to the column.
The remaining portion of the cooled high pressure residue gas
stream (45) is flashed (e.g., via an expansion valve to a lower
pressure then the other portion and is fed to the further
separation means (26) (22-D1200) (e.g., a LNGL separator). The
liquid (27) removed from the bottom of the further separation means
is a methane-rich liquid which is sent to an LNG storage vessel
(46) before being sent to the LNG production unit. The vapor stream
removed from the top of the further separation means (26) is
compressed in a boil-off gas (BOG) compressor (47) and removed as a
residue gas stream. [0268] The BOG compressor, compresses the
potentially nitrogen rich stream from the low pressure of the
liquefaction temperature to the final discharge pressure of the
residue gas compressor. This boil off gas is combined with other
residue gas at a point downstream of the removal of any portion of
residue gas that is to be used in the system. The potentially high
nitrogen concentration in the boil off gas renders it less suitable
for use in the system for cooling purposes.
[0269] FIG. 8 shows a further embodiment of the invention. In this
embodiment, a side stream is removed from the overhead vapor
product (12) of the LEFC (7) is used as feed for the LNG production
unit. The LEFC overhead vapor side stream, before being used as
feed for the LNG production unit is cooled and liquefied by a
standalone refrigeration source (REF). By using a cooled portion of
the LEFC overhead vapor as a feed to the LNG unit, the utility
consumption of the refrigeration unit is decreased and thereby the
process is rendered more energy efficient when compared to a
standalone LNG production unit. Additionally, using a portion of
the cold liquid from the LNG production unit as reflux for the LEFC
increases the efficiency and product recovery.
[0270] As shown in FIG. 8, prior to delivery to the subcooler (13)
a portion (23) of the LEFC overhead vapor is removed and introduced
as feed to the LNG production unit. In particular, this portion of
the LEFC overhead vapor is partially liquefied by heat exchange in
an LNGL heat exchanger (48) (i.e., a heat exchanger that combines
functions of the NGL LNG units) with refrigerant and with a residue
gas from the LNG production unit. The resulting stream partially
liquefied is fed to a further separation means such as a reflux
separator (26), where the majority of ethane as well as heavier
hydrocarbon components are separated as liquid, removed as bottom
liquid from the reflux separator (26), and returned to the LEFC as
reflux (27).
[0271] The methane-rich vapors (28) from the top of the reflux
separator (26) are further cooled by heat exchange in LNGL heat
exchanger (48) against refrigerant and boil off gas from the LNG
production unit. The resultant partially liquefied methane-rich
stream (29) is then flashed (e.g., by expansion in an expansion
valve) to a lower pressure and the resultant stream (41) is fed
into a further separator (50), i.e., a LNGL separator. The
methane-rich liquid methane-rich liquid removed the bottom of the
further separator (50) is optionally sent to an LNG storage vessel
(46) before being sent to further processing, if desired. The vapor
51 (i.e., boil off gas) removed from the top of the further
separator (50) is subjected to heat exchange in the LNGL exchanger
(48) to provide additional cooling for the portion of the LEFC
overhead vapor (23), and is then compressed in a BOG compressor
(47) and combined with residue gas from NGL recovery unit.
[0272] FIG. 9 shows a modification of the embodiment of FIG. 8. In
FIG. 8, the vapor (51, i.e., boil off gas, removed from the top of
the further separator (50) is subjected to heat exchange in the
LNGL exchanger (48) to provide additional cooling for the portion
of the LEFC overhead vapor (23), and is then compressed in the BOG
compressor (47) and combined with residue gas from NGL recovery
unit. However, in FIG. 9, this vapor (51) removed from the top of
the further separator (50) is compressed in the BOG compressor (47)
without previously being used in the LNGL exchanger (48) to provide
additional cooling for the portion of the LEFC overhead vapor (23).
Additionally, a residue gas (52) is introduced into the LNGL heat
exchanger (48), where it is cooled and liquefied. After exiting the
LNGL exchanger (48), the liquefied residue gas is flashed across a
valve, causing the fluid to reach even colder temperatures, and is
then fed back to LNGL heat exchanger (48) to provide further
cooling for the LNG production unit.
[0273] FIG. 10 shows an embodiment that is very similar to the
embodiment of FIG. 1, except that the treatment of the overhead
vapor stream (28) from the further separation means (26) differs.
Thus, as in FIG. 1, in the embodiment of FIG. 10 a side stream (23)
is taken from the overhead vapor product of the LEFC (7). The
partially liquefied vapor stream is delivered to a refrigerant
system where it undergoes indirect heat exchange with a refrigerant
fluid (REF). The resultant stream (25) is then fed into a further
separation means (26), such as a further gas/liquid separator or a
further distillation column. The majority of ethane and heavier
hydrocarbon components are recovered from the bottom of the further
separation means (26) as a liquid product stream (27) and returned
to the LEFC as a liquid reflux.
[0274] The overhead vapor stream (28) from the further separation
means (26), rich in methane, undergoes indirect heat exchange in an
LNGL heat exchanger with the refrigerant fluid of the refrigerant
system for additional cooling. This methane rich stream leaves the
LNGL exchanger as a cooled partially liquefied stream (29) and is
then flashed (e.g., by expansion in an expansion valve) to a lower
pressure. The resultant stream (41) is fed into a further separator
(50), i.e., a LNGL separator. The methane-rich liquid removed the
bottom of the further separator (50) is optionally sent to an LNG
storage vessel (46) before being sent to the LNG production unit.
The vapor removed from the top of the further separator (50) is
compressed in BOG compressor (47) and sent to residue gas, e.g.,
combined with other residue gas from NGL recovery unit.
[0275] FIG. 11 shows an embodiment which combines the embodiment of
FIG. 2 with that of FIG. 10. By using a portion of the cooled LEFC
overhead (23) as a feed to the LNG production unit, the utility
consumption of the refrigeration unit is decreased and thereby the
process is rendered more energy efficient when compared to a
standalone LNG production unit. Additionally, returning a portion
of the cold liquid from the LNG unit as well as streams from the
cold separator as reflux streams to the LEFC increases efficiency
and product recovery of the NGL recovery unit.
[0276] Thus, as in FIG. 2, additional reflux streams are provided
for the LEFC (22-T2000) in the embodiment of FIG. 11. Prior to
expansion, a portion (30) of the gaseous overhead stream (4) from
the cold separator (3) is fed to the subcooler (13) where it
undergoes indirect heat exchange with the overhead vapor from LEFC
(7). In the subcooler (13), this portion (30) is further cooled and
partially liquefied, and then expanded and introduced into the top
region of the LEFC (7) to thereby provide additional reflux
(31).
[0277] In addition, a portion (32) of bottoms liquid stream (8)
from cold separator (3) is delivered to a liquid/liquid heat
exchanger (33), where it undergoes indirect heat exchange with
bottom liquid (10) removed from the bottom of the LEFC (7). The
resultant stream (34) is then expanded and fed into an intermediate
region of the LEFC (7) as a liquid reflux.
[0278] Also, as in FIG. 10, in the embodiment of FIG. 11, the
methane-rich vapor stream that leaves LNGL exchanger as a partially
liquefied stream (29) is flashed (e.g., by expansion in an
expansion valve) to a lower pressure. The resultant stream (41) is
fed into a further separator (50), i.e., a LNGL separator. The
methane-rich liquid removed the bottom of the further separator
(50) is optionally sent to an LNG storage vessel (46) before being
sent to the LNG production unit. The vapor (boil off gas) (51)
removed from the top of the further separator (50) is compressed in
a BOG compressor (47) and sent to residue gas, e.g., combined with
other residue gas from NGL recovery unit.
[0279] FIG. 12 illustrates a system that combines the embodiment of
FIG. 3 with that of FIG. 10. As with the embodiment of FIG. 10, the
use of a portion (23) of the cooled LEFC overhead as a feed to the
LNG production unit decreases utility consumption of the
refrigeration unit and thereby renders the process more energy
efficient. Additionally, returning a portion of the cold liquid
from the LNG unit as well as streams from the cold separator as
reflux streams to the LEFC increases efficiency and product
recovery of the NGL recovery unit.
[0280] In FIG. 12, as in FIGS. 10 and 11, the methane rich stream
that leaves LNGL exchanger (48) as a cooled partially liquefied
stream (29) is flashed (e.g., by expansion in an expansion valve)
to a lower pressure. The resultant stream (41) is fed into a
further separator (50), i.e., a LNGL separator. The methane-rich
liquid removed the bottom of the further separator (50) is
optionally sent to an LNG storage vessel (46) before being sent to
the LNG production unit. The vapor (boil off gas) (51) removed from
the top of the further separator (50) is compressed in a BOG
compressor (47) and sent to residue gas, e.g., combined with other
residue gas from NGL recovery unit.
[0281] As in FIG. 3, the system of FIG. 12 provides additional
reflux streams for the LEFC (7). Prior to expansion in
turboexpander (5), a portion (30) is branched off from the gaseous
overhead stream (4) removed from the top of cold separator (3).
This portion (30) is combined with a portion of bottoms liquid
stream (32) removed from the bottom of the cold separator (3). The
combined stream (35) is fed to subcooler (13) where it undergoes
indirect heat exchange with the overhead vapor from LEFC (7).
Stream (35) is cooled and partially liquefied in the subcooler
(13), and then expanded and introduced into the top region of the
LEFC (7) to provide additional reflux. This additional reflux
stream for the LEFC (7) improves recovery of the ethane and heavier
hydrocarbon components.
[0282] FIG. 13 illustrates a system that combines the embodiments
of FIGS. 4 and 10. As with the embodiment of FIG. 10, the use of a
portion (23) of the cooled LEFC overhead as a feed to the LNG
production unit decreases utility consumption of the refrigeration
unit and thereby renders the process more energy efficient.
Additionally, returning a portion of the cold liquid from the LNG
unit as a reflux stream to the HEFC (see, e.g., FIG. 4), as well as
using streams from the cold separator as reflux streams for the
LEFC, increases efficiency and product recovery of the NGL recovery
unit.
[0283] As in FIG. 4, in the system of FIG. 13 the side stream (23)
taken from the overhead vapor product (12) of the LEFC undergoes
indirect heat exchange in the LNGL exchanger (48) with a
refrigerant fluid for cooling and is then fed into a further
separation means (26) (e.g., a further gas/liquid separator or
further distillation column). The methane-rich overhead vapor
stream (28) from the further separation means (26) undergoes
indirect heat exchange with the refrigerant fluid for additional
cooling in the LNGL exchanger (48). As in FIGS. 10 and 11, the
methane rich stream that leaves LNGL exchanger as a cooled
partially liquefied stream (29) is flashed (e.g., by expansion in
an expansion valve) to a lower pressure. The resultant stream (41)
is fed into a further separator (50), i.e., a LNGL separator. The
methane-rich liquid removed the bottom of the further separator
(22-D1200) is optionally sent to an LNG storage vessel (46) before
being sent to the LNG production unit. The vapor (boil off gas)
(51) removed from the top of the further separator (50) is
compressed in BOG compressor (47) and sent to residue gas, e.g.,
combined with other residue gas from NGL recovery unit.
[0284] As in FIG. 4, the system of FIG. 13 provides additional
reflux streams for both the LEFC (7) and the HEFC (9). The ethane
and heavier hydrocarbon components recovered from the bottom of the
further separation means (26) as liquid product (27) are introduced
into the top of the HEFC (9) as a liquid reflux stream, rather than
being sent to the LEFC (7). Also, prior to expansion in
turboexpander (5), a portion (30) is branched off from the gaseous
overhead stream (4) removed from the top of cold separator (3).
This portion (30) is combined with a portion of bottoms liquid
stream (32) removed from the bottom of the cold separator (3). The
combined stream (35) is fed to subcooler (13) where it undergoes
indirect heat exchange with the overhead vapor (12) from LEFC (7).
Stream (35) is cooled and partially liquefied in the subcooler
(22-E3200), and then expanded and introduced into the top region of
the LEFC (7) to provide additional reflux.
[0285] FIG. 14 illustrates a system that combines the embodiments
of FIGS. 5 and 10. As with the embodiment of FIG. 10, the use of a
portion (13) of the cooled LEFC overhead as a feed to the LNG
production unit decreases utility consumption of the refrigeration
unit and thereby renders the process more energy efficient.
Additionally, returning a portion of the cold liquid from the LNG
unit as a reflux stream to the LEFC (see, e.g., FIG. 5), as well as
using streams from the cold separator as reflux streams for the
LEFC, increases efficiency and product recovery of the NGL recovery
unit. Further, the incorporation of a refrigeration loop through
the NGL process results in further reduction in energy
consumption.
[0286] As in FIGS. 2 and 5, in FIG. 14 a side stream (23) is taken
from the overhead vapor product (12) of the LEFC and subjected to
indirect heat exchange (48) with a refrigerant fluid for further
cooling. This stream is then fed to a further separation means (26)
where the majority of ethane as well as heavier hydrocarbon
components are recovered as liquid product (27) and returned to the
LEFC (7) as a liquid reflux stream. The methane-rich overhead vapor
stream (28) from the further separation means (26) undergoes
indirect heat exchange with the refrigerant fluid for additional
cooling in the LNGL exchanger (48).
[0287] As in FIGS. 10-12, the methane rich stream that leaves LNGL
exchanger as a cooled partially liquefied stream (29) is flashed
(e.g., by expansion in an expansion valve) to a lower pressure. The
resultant stream (41) is fed into a further separator (50), i.e., a
LNGL separator. The methane-rich liquid removed the bottom of the
further separator (50) is optionally sent to an LNG storage vessel
(46) before being sent to the LNG production unit. The vapor (boil
off gas) (51) removed from the top of the further separator (50) is
compressed in a BOG compressor (47) and sent to residue gas, e.g.,
combined with other residue gas from NGL recovery unit.
[0288] Further, as in FIGS. 2 and 5, additional reflux streams are
provided for the LEFC (7). Prior to expansion of the gaseous
overhead stream (4), obtained from cold separator (3) in the
turboexpander (5), a portion (30) of the gaseous overhead stream
(4) is fed to the subcooler (13), where it undergoes indirect heat
exchange with the overhead vapor (12) from LEFC (7). In the
subcooler (13), portion (30) is cooled further and partially
liquefied, and then expanded and introduced into the top region of
the LEFC (7) to provide additional reflux. In addition, a portion
of bottoms liquid stream (32) removed from the bottom of the cold
separator (3) is delivered to a liquid/liquid heat exchanger (33),
where it undergoes indirect heat exchange with the bottom liquid
stream (10) removed from the bottom of the LEFC (7). The resultant
stream (34) is then fed to an intermediate region of the LEFC (7)
as a liquid reflux.
[0289] FIG. 14, however, further incorporates a refrigeration loop
through the NGL process which results in a reduction in energy
consumption. Specifically, a stream of refrigerant fluid (52) from
the refrigerant system is fed through the main heat exchanger (2)
(e.g., a plate-fin heat exchanger) where it undergoes indirect heat
exchange with the liquid product stream (15) from the bottom of the
HEFC (9), the further liquid stream (16) from an intermediate point
of the HEFC (9), the reboiler stream (18) removed from the bottom
region of the HEFC (22-T2100), and the overhead vapor product
stream (12) removed from the top of the LEFC (7). The refrigerant
stream, cooled and partially liquefied, leaves the main heat
exchanger as stream (53). Thereafter, the refrigerant stream is
introduced into the subcooler (13) where it is further cooled and
liquefied. This stream is then flashed across a valve causing the
fluid to reach even colder temperatures and is then fed (54) back
to the subcooler (13) to provide cooling to the reflux streams of
the LEFC (7). The refrigerant stream (55) then returns to the main
heat exchanger (22-E3000), where it serves as a coolant to the NGL
process streams. The refrigerant stream (56) is then returned to
the refrigeration system for compression. The incorporation of this
refrigeration loop through the NGL process results in a reduction
in energy consumption.
[0290] FIG. 15 shows a system that is a modification of the system
of FIG. 14 that combines features of the embodiments of FIGS. 6 and
10. Thus, FIG. 15 illustrates an embodiment which is similar to
that shown in FIG. 14, but with a modified refrigeration loop. A
stream of refrigerant fluid (52) from the refrigerant system is fed
through the main heat exchanger (2) where it undergoes indirect
heat exchange with the liquid product stream (15) from the bottom
of the HEFC (9), the further liquid stream (16) from an
intermediate point of the HEFC (9), the reboiler stream (18)
removed from the bottom region of the HEFC (9), and the overhead
vapor product stream (12) removed from the top of the LEFC (7). The
refrigerant stream, cooled and partially liquefied, leaves the main
heat exchanger (2) as stream (53). Thereafter, the refrigerant
stream is introduced into the subcooler (13) where it is further
cooled and liquefied. This stream is then introduced into a heat
exchanger (48) for cooling the side stream (23) from the LEFC
overhead vapor product stream (12). The refrigerant stream exits
heat exchanger (48) and is flashed across a valve, causing the
fluid to reach even colder temperatures. The resultant stream (54)
is then fed back to the same heat exchanger (48) to provide further
cooling. Thereafter, the refrigerant passes through the subcooler
(13) and the main heat exchanger (2), and then flows to the
refrigeration system for compression. Here again, the incorporation
of a refrigeration loop through the NGL process results in a
reduction in energy consumption.
[0291] FIG. 16 shows a further embodiment of the invention. In this
embodiment, like in the embodiment of FIG. 7, a side stream is not
removed from the overhead vapor product (12) of the LEFC before the
latter is sent to the subcooler (13). Instead, after the overhead
vapor product of the LEFC passes through the subcooler (13), it is
sent to the main heat exchanger, and then at least portion thereof
is compressed. At least a portion of this compressed residue gas is
used as feed for the LNG production unit and to provide a reflux
stream for the LEFC. Using the residue gas as a feed to the LNG
unit reduces the utility consumption of the refrigeration unit
thereby rendering the process more energy efficient when compared
to a standalone LNG unit. Also, returning a portion of the cold
liquid from the LNG production unit as reflux for the LEFC
increases the efficiency and product recovery of the NGL recovery
unit.
[0292] As shown in FIG. 16, overhead vapor (12) obtained from the
top of the LEFC, passes through the subcooler (13) and the main
heat exchanger (2). The resultant stream (57) is compressed in
compressor (58), and then recycled (59) to a LNGL heat exchanger
(48) wherein it is cooled and partially liquefied by heat exchange
with refrigerant. The resulting stream is fed to a further
separation means such as a reflux separator (26). The majority of
ethane and heavier hydrocarbon components are removed as a liquid
stream (27) from the bottom of the reflux separator (26) and
returned to the LEFC as reflux. The methane-rich vapor stream (28)
removed from the top of the reflux separator (26) is sent to the
LNGL heat exchanger (48) where it undergoes heat exchange with the
refrigerant for additional cooling. The resultant partially
liquefied stream (29) exits the LNGL heat exchanger (48) and is
flashed (e.g., by expansion in an expansion valve) to a lower
pressure, and fed as stream (41) to an LNGL separator (50). A
methane-rich liquid is recovered and from the LNGL separator (50)
and optionally sent to an LNG storage vessel (46). The vapor (boil
off gas) (51) from the LNGL separator is compressed in a BOG
compressor (47) and sent to residue gas, e.g., combined with other
residue gas from NGL recovery unit.
[0293] As noted above, FIGS. 17-21 are modifications of the Gas
Subcooled
[0294] Process. In FIG. 17, gas feed stream (1), containing, for
example, helium, nitrogen methane, ethane, ethylene, and C3+
hydrocarbons (e.g., a natural gas feed stream) is introduced into
the system at a temperature of, e.g., 4 to 60.degree. C. and a
pressure of, e.g., 300 to 1500 psig. The gas feed stream (1) is
split into two partial feed streams, first partial feed stream (1A)
and second partial feed stream (1B). The first partial feed stream
(1A) is cooled and partially condensed by indirect heat exchange in
a main heat exchanger (2) against process streams (16, 18, 15),
e.g., streams originating from a demethanizer. The second partial
feed stream (1B) is cooled and partially condensed by indirect heat
exchange in another heat exchanger (60) against a process stream
(12), e.g., an overhead stream from a demethanizer (this heat
exchanger can share a common core with another heat exchanger,
e.g., the subcooler described below). These two partial feed
streams are then recombined (10), optionally further cooled (61)
(e.g., by indirect heat exchange against a refrigerant), and then
introduced into a gas/liquid cold separator (3).
[0295] The gaseous overhead stream (4) removed from the top of the
cold separator (3) is split into two potions (30, 30A). Similarly,
the bottoms liquid stream (8) from the cold separator (22-D1000) is
also split into two potions (32, 32A).
[0296] A first portion of the gaseous overhead stream (30A) is
expanded, for example, in a turboexpander (5), which can be
optionally coupled to a compressor (63) and then introduced (6)
into an intermediate region of a demethanizer column (62) at a
first intermediate point. A first portion of the bottoms liquid
stream (32A) from the cold separator (3) is also introduced and
expanded into an intermediate region of a demethanizer column (62)
at a second intermediate point which is below the first
intermediate point, i.e., the point of introduction of the first
portion of the gaseous overhead stream (6). The second portion of
the gaseous overhead stream (30) is combined with the second
portion of the bottoms liquid stream (32) to form a combined cold
separator stream (35), which is then cooled in a subcooler (13) by
indirect heat exchange with an overhead vapor stream (12) from the
top of the demethanizer (62). Stream (35) is then introduced and
expanded into the upper region of the demethanizer. The
demethanizer column (62) typically operates at a temperature of -70
to -115.degree. C. and a pressure of 100 to 500 psig.
[0297] A liquid product stream is removed from the bottom of the
demethanizer (62) and sent to a product surge vessel (20). Liquid
from the product surge vessel) can be recycled to the bottom region
of the demethanizer (62). The liquid product stream (15) from the
product surge vessel (20) is heated by heat exchange, for example,
by passage through the main heat exchanger (2) where it can undergo
indirect heat exchanger with the first partial feed stream (1A). In
addition, a further liquid stream (16) is removed from a third
intermediate point of the demethanizer, i.e., below the second
intermediate point. This further liquid stream (16) is heated by
indirect heat exchange, e.g., in the main heat exchanger (2)
against first partial feed stream (1A), and then reintroduced (17)
into the demethanizer at a fourth intermediate point i.e., below
the third intermediate point. An additional liquid stream (18) is
removed from the lower region of the demethanizer, i.e., below the
fourth intermediate point. This further liquid stream (18) is
heated by indirect heat exchange, e.g., in the main heat exchanger
(2), acting here as a reboiler, against first partial feed stream
(1A), and then reintroduced (19) into the lower region of the
demethanizer. Further, as noted above, an overhead vapor stream
(12) is removed from the top of the demethanizer (62)).
[0298] A high pressure (e.g., 300 to 1500 psig) residue gas stream
is introduced into the system and cooled by indirect heat exchange
in heat exchanger (60) against a process stream (12), e.g., an
overhead stream from a demethanizer, further cooled in the
subcooler (13), and optionally further cooled in a further heat
exchanger (e.g., an LNGL exchanger). A portion (65) of this cooled
high pressure reside gas stream is expanded (e.g., via an expansion
valve) to the operating pressure of the demethanizer (62), combined
with the combined cold separator stream (35) and then introduced
into the upper region of the demethanizer (62) as the top feed
thereof. The remaining portion of the cooled high pressure residue
gas stream is expanded (e.g., via an expansion valve) to a pressure
below the operating pressure of the demethanizer and fed to a
further separation means, e.g., an LNGL separator (50). A methane
rich liquid stream is removed from the further separation means
(50), optionally stored in an LNG storage vessel (46), before being
sent to the LNG production unit. The overhead vapor (boil off gas)
(51) from the further separation means is compressed in a BOG
compressor (47) and sent to residue gas, e.g., combined with other
residue gas from NGL recovery unit
[0299] The embodiment of FIG. 18 involves the use of a side stream
from the overhead vapor stream of the demethanizer, rather than the
high pressure residue gas stream of the embodiment of FIG. 17.
Thus, in FIG. 18, a portion of the cooled overhead vapor (12) from
the demethanizer (62) is used as feed for the LNG production
unit.
[0300] Before being cooled in the subcooler (13), a side stream
(23) is separated from the overhead vapor stream (12) of the
demethanizer and is partially liquefied by heat exchange in an LNGL
heat exchanger (48) against a refrigerant. The resulting stream is
fed to a further separation means such as a reflux separator (26).
In the reflux separator the majority of ethane and higher
hydrocarbon components are removed as a bottom liquid stream (27)
and returned to the demethanizer as reflux. A methane-rich vapor
stream (28) is removed from the top of the reflux separator (26),
cooled by heat exchange against the refrigerant in the LNGL heat
exchanger (48) and at least partially liquefied therein. The at
least partially liquefied stream (29) exits the LNGL exchanger, is
flashed-expanded via an expansion valve to a lower pressure and fed
into a further separation means (50) (e.g., an LNGL separator). A
methane-rich rich liquid is recovered from the bottom of the
further separation means (50) and optionally stored in the LNG
storage vessel (46) before being sent as feed to the LNG production
unit. A vapor stream (51) (boil off gas) is removed from the top of
the further separation means (50) and used in the LNGL heat
exchanger (48) to provide additional cooling for the side stream
(23) from the demethanizer overhead vapor stream (12) and the
methane-rich vapor stream (28) removed from the top of the reflux
separator (26). The vapor stream (51) from the top of the further
separation means is then compressed in a BOG compressor (47) and
combined with other residue gas from the GSP unit.
[0301] The embodiment of FIG. 19 is similar to the embodiment of
FIG. 18, except that additional cooling in the LNGL heat exchanger
(48) is achieved by the initially cooling and liquefying a residue
gas stream which is then expanded and sent back to the LNGL heat
exchanger (48) as a cooling medium.
[0302] Thus, in FIG. 19 the side stream (23) from the overhead
vapor stream (12) of the demethanizer is partially liquefied by
heat exchange in an LNGL heat exchanger (48)) against a
refrigerant. The resulting stream is fed to a further separation
means such as a reflux separator (26). The bottom liquid stream
(27) (mostly ethane and higher hydrocarbon components) is returned
to the demethanizer as reflux. The methane-rich vapor stream (28)
is cooled by heat exchange against the refrigerant in the LNGL heat
exchanger (48) and at least partially liquefied therein. The at
least partially liquefied stream (29) exits the LNGL exchanger
(48), is flashed-expanded via an expansion valve to a lower
pressure and fed (41) into a further separation means (50) (e.g.,
an LNGL separator (22-D1200)). A methane-rich rich liquid is
recovered from the bottom of the further separation means (50) and
optionally stored in the LNG storage vessel (46) before being sent
as feed to the LNG production unit. A vapor stream (51) (boil off
gas) is removed from the top of the further separation means (50),
compressed in a BOG compressor (47), and combined with other
residue gas from the GSP unit.
[0303] A residue gas (67) is introduced into the LNGL exchanger
(48), where it is cooled and liquefied. The residue gas exits the
LNGL exchanger and is flashed across a valve, causing the fluid to
reach even colder temperatures. The resultant stream (68) is then
fed back to the LNGL exchanger (48) to provide additional cooling
for the side stream (23) from the demethanizer overhead vapor
stream (12) and the methane-rich vapor stream (28) removed from the
top of the reflux separator (26).
[0304] FIG. 20 illustrates an embodiment similar to that of FIGS.
18 and 19. However, in the embodiment of FIG. 20 no additional
cooling, such as from residue gas (67) or the vapor stream from the
top of the further separation means (50), is used in the LNGL heat
exchanger (48).
[0305] Like FIGS. 18-20, the embodiment of FIG. 21 involves the use
of a side stream originating from the overhead vapor stream of the
demethanizer. However, in this case, the side stream is separated
from the overhead vapor stream of the demethanizer after the latter
has undergone further cooling (i.e., in subcooler (13) an heat
exchanger (60). Also, the side stream is compressed before it is
introduced into the LNGL exchanger (48).
[0306] As shown in FIG. 21, the overhead vapor stream (23) from the
top of the demethanizer passes through the subcooler (13) and the
heat exchanger (60) that cools the second partial feed stream (1B).
Thereafter, at least a portion of the overhead vapor stream is
compressed in compressor (63) (which is coupled to expander (5)) to
form a residue gas. Then, a portion of this residue gas is cooled
and partially liquefied by heat exchange in an LNGL heat exchanger
(48) against a refrigerant. The resulting stream is fed to a
further separation means such as a reflux separator (26).
[0307] In the reflux separator (26) the majority of ethane and
higher hydrocarbon components are removed as a bottom liquid stream
(27) and returned to the demethanizer (62) as reflux. A
methane-rich vapor stream (28) is removed from the top of the
reflux separator (26), cooled by heat exchange against the
refrigerant in the LNGL heat exchanger (48) and at least partially
liquefied therein. The at least partially liquefied stream (29)
exits the LNGL exchanger, is flashed-expanded via an expansion
valve to a lower pressure and fed (41) into a further separation
means (50) (e.g., an LNGL separator). A methane-rich rich liquid is
recovered from the bottom of the further separation means (50) and
optionally stored in the LNG storage vessel (46) before being sent
as feed to the LNG production unit. A vapor stream (boil off gas)
(51) is removed from the top of the further separation means (50),
compressed in a BOG compressor (47), and combined with other
residue gas from the GSP unit.
[0308] As noted above, FIGS. 22-26 are modifications of the Recycle
Split Vapor Process. As shown in FIG. 22, gas feed stream (1),
containing, for example, helium, nitrogen methane, ethane,
ethylene, and C3+ hydrocarbons (e.g., a natural gas feed stream) is
introduced into the system at a temperature of, e.g., 4 to
60.degree. C. and a pressure of, e.g., 300 to 1500 psig. The gas
feed stream (1) is split into two partial feed streams, a first
partial feed stream (1A) and second partial feed stream (1B). The
first partial feed stream (1A) is cooled and partially condensed by
indirect heat exchange in a main heat exchanger (2) against process
streams (16, 18, 15). The second partial feed stream (1B) is cooled
and partially condensed by indirect heat exchange in another heat
exchanger (60) against a process stream (12), e.g., an overhead
stream from a demethanizer (62) (this heat exchanger can share a
common core with another heat exchanger, e.g., the subcooler
described below). These two partial feed streams are then
recombined (10), optionally further cooled (61) (e.g., by indirect
heat exchange against a refrigerant), and then introduced into a
gas/liquid cold separator (3).
[0309] The gaseous overhead stream (4) removed from the top of the
cold separator (3) is split into two potions (30, 30A). Similarly,
the liquid bottom stream (8) from the cold separator (3) is also
split into two potions (32, 32A).
[0310] A first portion of the gaseous overhead stream (30A) is
expanded, for example, in a turboexpander (5), which can be
optionally coupled to a compressor (63) and then introduced (6)
into an intermediate region of a demethanizer column (62) at a
first intermediate point. A first portion of the bottoms liquid
stream (32A) from the cold separator (3) is also expanded and
introduced into an intermediate region of a demethanizer column
(62) at a second intermediate point which is below the first
intermediate point, i.e., the point of introduction of the first
portion of the gaseous overhead stream (6). The second portion of
the gaseous overhead stream (30) is combined with the second
portion of the bottoms liquid stream (32) to form a combined cold
separator stream (35), which is then cooled in a subcooler (13) by
indirect heat exchange with an overhead vapor stream (12) from the
top of the demethanizer (22-T2000), and expanded and introduced
into the upper region of the demethanizer as a top feed thereof.
The demethanizer column (22-T2000) typically operates at a
temperature of -70 to -115.degree. C. and a pressure of 100 to 500
psig.
[0311] A liquid product stream is removed from the bottom of the
demethanizer (62) and sent to a product surge vessel (20). Liquid
from the product surge vessel can be recycled to the bottom region
of the demethanizer (62). The liquid product stream (15) from the
product surge vessel (2) is heated by heat exchange, for example,
by passage through the main heat exchanger (2) where it can undergo
indirect heat exchanger with the first partial feed stream (1A). In
addition, a further liquid stream (18) is removed from a third
intermediate point of the demethanizer, i.e., below the second
intermediate point. This further liquid stream (16) is heated by
indirect heat exchange, e.g., in the main heat exchanger (2)
against first partial feed stream (1A), and then reintroduced (17)
into the demethanizer at a fourth intermediate point i.e., below
the third intermediate point. An additional liquid stream (18) is
removed from the lower region of the demethanizer, i.e., below the
fourth intermediate point. This further liquid stream (18) is
heated by indirect heat exchange, e.g., in the main heat exchanger
(2) (in this case acting as a reboiler) against first partial feed
stream (1A), and then reintroduced (19) into the lower region of
the demethanizer. Further, as noted above, an overhead vapor stream
(12) is removed from the top of the demethanizer (62).
[0312] A high pressure (e.g., 300 to 1500 psig) residue gas stream
(69) is introduced into the system and cooled by indirect heat
exchange in the subcooler (13). At least a portion of this residue
gas stream (69) is then expanded (e.g., via an expansion valve) to
the operating pressure of the demethanizer and introduced (70) into
the upper region of the demethanizer as another top feed
thereof.
[0313] Another portion (23) of the residue gas stream is expanded
(e.g., via an expansion valve) to a pressure below the operating
pressure of the demethanizer and fed to a further separation means
(50), e.g., an LNGL separator. A methane rich liquid stream is
removed from the further separation means (50) and optionally
stored in an LNG storage vessel (22-D1300), before being sent to
the LNG production unit. The overhead vapor stream (boil off gas)
(51) removed from the further separation means (50) is compressed
in a BOG compressor (47) and combined with other residue gas from
the GSP unit.
[0314] FIG. 23 shows an embodiment which is the same as the
embodiment of FIG. 222, except that the subcooler (13) is split
into two separate exchangers (13A) and (13B). Thus, in subcooler
(13A) the residue gas stream (6 (is cooled by heat exchange with a
portion of the demethanizer overhead stream (12), and in subcooler
(13B) the combined cold separator stream (35) is cooled by heat
exchange with another portion (12A) of the demethanizer overhead
stream.
[0315] The embodiment of FIG. 24 is similar to the embodiment of
FIG. 23, except that the side stream (23) from the residue gas
stream (69) is treated in a manner similar to the treatment of side
stream (232) in FIG. 18. Thus, after residue gas stream (69) is
cooled in the subcooler (13), a side stream (23) is separated
therefrom and is partially liquefied by heat exchange in an LNGL
heat exchanger (48) against a refrigerant. The resulting stream is
fed to a further separation means such as a reflux separator (26).
In the reflux separator the majority of ethane and higher
hydrocarbon components are removed as a bottom liquid stream (27)
and returned to the demethanizer as reflux. A methane-rich vapor
stream (28) is removed from the top of the reflux separator (26),
cooled by heat exchange against the refrigerant in the LNGL heat
exchanger (48) and at least partially liquefied therein. The at
least partially liquefied stream (29) exits the LNGL exchanger, is
flashed-expanded via an expansion valve to a lower pressure and fed
into a further separation means (50) (e.g., an LNGL separator). A
methane-rich rich liquid is recovered from the bottom of the
further separation means (50) and optionally stored in the LNG
storage vessel (46) before being sent as feed to the LNG production
unit. A vapor stream (51) (boil off gas) is removed from the top of
the further separation means (50) and used in the LNGL heat
exchanger (48) to provide additional cooling for the side stream
(23) from the demethanizer overhead vapor stream (12) and the
methane-rich vapor stream (28) removed from the top of the reflux
separator (26). The vapor stream (51) from the top of the further
separation means is then compressed in a BOG compressor (47) and
combined with other residue gas from the RSV unit.
[0316] The embodiment of FIG. 25 treats the high pressure residue
gas stream, which is cooled by indirect heat exchange in the
subcooler, in a manner similar to the way that the side stream from
the overhead vapor stream of the demethanizer is treated in FIG.
19. As shown in FIG. 25, the high pressure residue gas stream (69)
is cooled by indirect heat exchange in the subcooler (13), and then
divided into a first portion (70) and a second portion (23). The
first portion (70) of the residue gas stream is expanded (e.g., via
an expansion valve) to the operating pressure of the demethanizer
and introduced into the upper region of the demethanizer as a top
feed thereof. The second portion (23) of the residue gas stream is
cooled and partially liquefied by heat exchange in an LNGL heat
exchanger (48) against a refrigerant. The resulting stream is fed
to a further separation means such as a reflux separator (26).
[0317] In the reflux separator, the majority of ethane and higher
hydrocarbon components are removed as a bottom liquid stream (27)
and returned to the demethanizer as reflux. A methane-rich vapor
stream (28) is removed from the top of the reflux separator (26),
cooled by heat exchange against the refrigerant in the LNGL heat
exchanger (48) and at least partially liquefied therein. The at
least partially liquefied stream (29) exits the LNGL exchanger, is
flashed-expanded via an expansion valve to a lower pressure and fed
(41) into a further separation means (50) (e.g., an LNGL
separator). A methane-rich rich liquid is recovered from the bottom
of the further separation means and optionally stored in the LNG
storage vessel (46) before being sent as feed to the LNG production
unit. A vapor stream (boil off gas) (51) is removed from the top of
the further separation means, compressed in a BOG compressor (47)
and combined with other residue gas from the RSV unit.
[0318] A residue gas (67) is introduced into the LNGL exchanger
(48), where it is cooled and liquefied. The residue gas exits the
LNGL exchanger (48) and is flashed across a valve, causing the
fluid to reach even colder temperatures. The resultant stream (68)
is then fed back to the LNGL exchanger to provide additional
cooling for the second portion of the residue gas stream (23) and
the methane-rich vapor stream (28) removed from the top of the
reflux separator (26).
[0319] FIG. 26 illustrates an embodiment similar to that of FIGS.
24 and 25. However, in the embodiment of FIG. 26 no additional
cooling, such as from residue gas (23) or the vapor stream (28)
from the top of the further separation means, is used in the LNGL
heat exchanger (48). Compare FIG. 20.
[0320] The embodiment of FIG. 27 is similar to the embodiments of
FIGS. 23-25, except that the residue gas that is cooled in the LNGL
heat exchanger originates from the overhead vapor stream of the
demethanizer. See FIG. 21.
[0321] As shown in FIG. 27, a high pressure residue gas stream (69)
is cooled by indirect heat exchange in the subcooler (13), and then
expanded (e.g., via an expansion valve) to the operating pressure
of the demethanizer and introduced into the upper region of the
demethanizer as a top feed thereof. Thus, unlike the embodiments of
FIGS. 24-26, the high pressure residue gas stream that exits the
subcooler is not divided into a first portion and a second
portion.
[0322] As shown in FIG. 27, the overhead vapor stream 12 from the
top of the demethanizer (62) passes through the subcooler (13) and
the heat exchanger (60) that cools the second partial feed stream
(1B). Thereafter, at least a portion of the overhead vapor stream
is compressed in compressor (63) (which is shown as being coupled
to expander C6000) to form a residue gas. Then, a portion of this
residue gas (59) is cooled and partially liquefied by heat exchange
in an LNGL heat exchanger (48) against a refrigerant. The resulting
stream is fed to a further separation means such as a reflux
separator (26).
[0323] In the reflux separator (26) the majority of ethane and
higher hydrocarbon components are removed as a bottom liquid stream
(27) and returned to the demethanizer as reflux. A methane-rich
vapor stream (28) is removed from the top of the reflux separator
(26), cooled by heat exchange against the refrigerant in the LNGL
heat exchanger (48) and at least partially liquefied therein. The
at least partially liquefied stream (29) exits the LNGL exchanger
(48), is flashed-expanded via an expansion valve to a lower
pressure and fed (41) into a further separation means (50) (e.g.,
an LNGL separator). A methane-rich rich liquid is recovered from
the bottom of the further separation means and optionally stored in
the LNG storage vessel (46) before being sent as feed to the LNG
production unit. A vapor stream (boil off gas) (51) is removed from
the top of the further separation means from the top of the further
separation means, compressed in a BOG compressor (47) and combined
with other residue gas from the RSV unit.
[0324] Without further elaboration, it is believed that one skilled
in the art can, using the preceding description, utilize the
present invention to its fullest extent. The preceding preferred
specific embodiments are, therefore, to be construed as merely
illustrative, and not limitative of the remainder of the disclosure
in any way whatsoever.
[0325] The preceding examples can be repeated with similar success
by substituting the generically or specifically described reactants
and/or operating conditions of this invention for those used in the
preceding examples.
[0326] The entire disclosure[s] of all applications, patents and
publications, cited herein and of priority U.S. provisional
Application No. 61/746,727, filed Dec. 28, 2012 are incorporated by
reference herein.
[0327] From the foregoing description, one skilled in the art can
easily ascertain the essential characteristics of this invention
and, without departing from the spirit and scope thereof, can make
various changes and modifications of the invention to adapt it to
various usages and conditions.
* * * * *