Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
TITLE
Producing LNG from Methane Containing Synthetic Gas
BACKGROUND
[0001] The present invention relates to a method and system for
producing liquefied
natural gas (LNG) from methane-containing synthetic gas (MCSG).
[0002] The evolution of environmentally friendly fuel technology has
resulted in the
integration of gasification and natural gas liquefaction process to produce
LNG from MCSG.
MCSG is a light hydrocarbon-containing gas comprising methane and impurities
lighter than
methane that can be produced from the gasification of coal or oil residues.
Making MCSG
from gasification products is a clean way of using traditionally solid and low-
value heavy liquid
fuels by allowing centralized carbon capture and sequestration while the clean
low-carbon
containing methane is produced and distributed. Additionally, co-production of
LNG from a
gasification process provides an attractive option to diversify a product
portfolio, thus
improving the overall economics of a project.
[0003] An exemplary prior art process for producing LNG from MCSG is
depicted and
described in US patent 10,436,505. In the process depicted therein, a
hydrocarbon-
containing feed gas stream, such as a syngas stream, is cooled to a relatively
warm
temperature of -30 to -130 C in a main heat exchanger that utilizes a
vaporizing mixed
refrigerant to provide the refrigeration. The cooled feed gas stream exiting
the main heat
exchanger is further cooled in a reboiler which provides heat for boilup in a
secondary
distillation column (lower operating pressure). The cooled feed gas stream
exiting the reboiler
is then further cooled to a temperature -120 to -200 C and at least partially
liquefied in the
main heat exchanger before being flashed and separated in a drum to form a
flashed vapor
stream and a liquid stream. The flashed vapor stream is expanded in the
expander portion of
a compander and routed to the rectification section of a primary distillation
column (higher
- 1 -
Date Recue/Date Received 2022-06-27
operating pressure). The liquid stream is let down in pressure via a valve and
routed to the
bottom of the primary distillation column.
[0004] A stream of bottoms liquid withdrawn from the primary
distillation column is routed
to the secondary distillation column to further improve methane recovery. A
stream of bottoms
liquid withdrawn from the secondary distillation column is cooled to a final
temperature of -
120 to -200 C in the main heat exchanger to form the LNG product stream. A
stream of
overhead vapor from the secondary distillation column is condensed in the main
heat
exchanger and flashed in reflux drum. The reflux drum liquid is used as reflux
for both the
primary and secondary distillation columns. The reflux drum vapor is
compressed in the
compression portion of the compander and is joined with the overhead vapour
from the
primary distillation column to form a stream of residue gas that is warmed in
the main heat
exchanger and recompressed in a residue gas compressor before being routed out
of the
facility.
[0005] A standard heat pump configuration using a two-stage compressor
and a JT valve
is used to provide cold refrigerant and hence refrigeration to the main heat
exchanger.
[0006] The configuration shown in US patent 10,436,505 can produce high
purity
methane-rich LNG, but it does have certain disadvantages. One issue is that
the mixed
refrigerant stream is introduced into the main heat exchanger as a two-phase
mixture. This
complicates the design of the piping and may cause undesirable unsteady
operation due to
slugging. Also, two-phase flow requires special design features of the main
heat exchanger
to ensure that the liquid and vapor phases are evenly distributed. For
example, if the main
heat exchanger is a plate-fin exchanger, special devices such as a separator
and injection
tubes must be provided to evenly distribute the phases across all passages.
The use of these
devices adds cost and can reduce operation stability. Additionally, the two-
phase flow may
become unstable at low flowrates causing disengagement of the phases resulting
in large
internal temperature gradients and potential damage to the main heat
exchanger.
[0007] Another disadvantage is that the main exchanger utilises two
different low pressure
streams for provide cooling duty to the heat exchanger (i.e. the cold
vaporizing mixed
refrigerant stream and the residue gas stream), which practically precludes
the use of a coil-
wound type heat exchanger as the main heat exchanger. Coil-wound heat
exchangers are
- 2 -
Date Recue/Date Received 2022-06-27
proven to be efficient, reliable, and robust for natural gas liquefaction and
end flash gas heat
exchange applications. The design and manufacturing technology of coil-wound
heat
exchangers allows much higher unit processing capacity (heat exchange duty
achieved per
coil-wound heat exchanger unit), avoiding using multiple heat exchanger units
(in the case of
plate fine heat exchanger) in parallel up to very large capacities. A coil-
wound heat exchanger
unit comprises one or more tube bundles encased in a shell casing, the tube
side of the unit
being designed to receive one or more hot streams that require cooling, and
the shell side of
the unit being designed to receive a single stream of cold refrigerant or two
or more cold
streams that mix in the shell side and exit as a single stream of warmed
refrigerant. The only
way that a coil-wound heat exchanger could accommodate the use of two or more
cold
streams that are to be kept separate would be to pass at least one of the cold
streams through
one of the passages on the tube side of the heat exchanger. However, the
design of the coil-
wound exchanger would then be difficult given the low available pressure drop
and the
relatively high typical resistance in the passages on the tube side of the
heat exchanger.
[0008] A further disadvantage of the depicted process is that all of the
residue gas is
produced at a relatively low pressure. This increases the operating and
capital costs of the
process, as the larger the amount of residue gas produced at low pressure the
greater the
power requirement for recompressing said gas and the larger the residue gas
compressor
has to be to accommodate said gas.
BRIEF SUMMARY
[0009] Disclosed herein are methods and systems for producing LNG from
MCSG that
provide several advantages over the prior art described above. The methods and
systems
may employ a single distillation column (instead of two or more columns). A
coil-wound heat
exchanger unit may be used that is separate from the heat exchanger unit(s)
used to recover
refrigeration from the residue gas streams, which coil-wound heat exchanger
unit may receive,
cool, and partially liquefy a portion of the MCSG feed stream, and/or which
may receive and
cool the refrigerant (such as a mixed refrigerant or other vaporizing
refrigerant) that is then
used for cooling and partially liquefying the MCSG feed stream. A portion of
the residue gas
- 3 -
Date Recue/Date Received 2022-06-27
may be rejected at substantially the same pressure as the MCSG feed stream and
require
relatively little or no recompression.
[0010] Several preferred aspects of the systems and methods according to
the present
invention are outlined below.
[0011] Aspect 1: A method for producing liquefied natural gas (LNG) from
methane
containing synthetic gas (MCSG), the method comprising:
(a) cooling and partially liquefying a MCSG feed stream to produce a
partially
liquefied MCSG feed stream;
(b) using a first phase separator and a second phase separator arranged in
series,
with the second phase separator being in downstream fluid flow communication
with the first
phase separator, to separate the partially liquefied MCSG feed stream into at
least three
streams comprising a liquid stream and two vapor streams, the liquid stream
forming a first
feed stream, one of the vapor streams forming a second feed stream, and the
other of the
vapor streams forming a first residue gas stream;
(c) introducing the first feed stream into a distillation column at a first
location;
(d) introducing the second feed stream into the distillation column at a
second
location that is above the first location, there being at least one separation
stage between the
first location and second location;
(e) withdrawing an LNG stream from the distillation column comprising
distillation
column bottoms liquid; and
(f) withdrawing a second residue gas stream from the distillation column
comprising distillation column overhead vapor.
[0012] Aspect 2: The method of Aspect 1, wherein step (b) comprises:
(i) separating the partially liquefied MCSG feed stream in the first phase
separator into the liquid stream that forms the first feed stream, and a vapor
stream;
(ii) dividing the vapor stream from the first phase separator to form the
vapor stream that forms the second feed stream, and a vapor stream that forms
a third
feed stream; and
(iii) cooling and partially liquefying the third feed stream and then
separating the third feed stream in the second phase separator into the vapor
stream
- 4 -
Date Recue/Date Received 2022-06-27
that forms the first residue gas stream, and a liquid stream that forms a
fourth feed
stream;
wherein step (c) comprises reducing the pressure of the first feed stream and
then
introducing the first feed stream into a distillation column at the first
location;
wherein step (d) comprises reducing the pressure of the second feed stream and
then
introducing the second feed stream into the distillation column at the second
location; and
wherein the method further comprises reducing the pressure of the fourth feed
stream
and then introducing the fourth feed stream into the distillation column at a
third location that
is above the second location, there being at least one separation stage
between the second
location and third location.
[0013]
Aspect 3: The method of Aspect 2, wherein the third location is at the top of
the
distillation column.
[0014]
Aspect 4: The method of Aspect 2 or 3, wherein one or both of the first
residue
gas stream and the second residue gas stream are warmed via indirect heat
exchange with
the third feed stream in order to provide cooling duty for the cooling and
partial liquefaction of
the third feed stream in step (b)(iii).
[0015] Aspect 5: The method of Aspect 1, wherein step (b) comprises:
(i) separating the partially liquefied MCSG stream in the first phase
separator into the vapor stream that forms the first residue gas stream, and a
liquid
stream that forms a third feed stream; and
(ii) reducing the pressure of and partially vaporizing the third feed
stream
and separating said stream in the second phase separator into the liquid
stream that
forms the first feed stream and the vapor stream that forms the second feed
stream;
and
wherein step (c) comprises warming the first feed stream and then introducing
the first
feed stream into a distillation column at the first location.
[0016]
Aspect 6: The method of Aspect 5, wherein there is at least one separation
stage
between the second location and the top of the column, and the method further
comprises:
compressing, cooling, expanding, and thereby at least partially liquefying a
portion of the
second residue gas stream or distillation column overhead vapor to form a
reflux stream; and
- 5 -
Date Recue/Date Received 2022-06-27
introducing the reflux stream into the distillation column at a third location
that is at the top of
the distillation column.
[0017]
Aspect 7: The method of Aspect 5 or 6, wherein in step (c) the first feed
stream is
warmed via indirect heat exchange with the MCSG feed stream in order to
provide cooling
duty for the cooling and partial liquefaction of the MCSG feed stream in step
(a).
[0018]
Aspect 8: The method of any one of Aspects 1 to 7, wherein one or both of the
first residue gas stream and the second residue gas stream are warmed via
indirect heat
exchange with the MCSG feed stream in order to provide cooling duty for the
cooling and
partial liquefaction of the MCSG feed stream in step (a).
[0019] Aspect 9: The method of any one of Aspects 1 to 8, wherein there is
at least one
separation stage between the first location and the bottom of the column, and
wherein the
method further comprises warming and thereby at least partially vaporizing a
portion of the
LNG stream or distillation column bottoms liquid to form a boil-up stream, and
introducing the
boil-up stream into the distillation column at the bottom of the distillation
column.
[0020] Aspect 10: The method of any one of Aspects 1 to 9, wherein at least
a portion of
the second residue gas stream is compressed and combined with first residue
gas stream.
[0021]
Aspect 11: The method of any one of Aspects 1 to 10, wherein the method
further
comprises subcooling the LNG stream.
[0022]
Aspect 12: The method of any one of Aspects 1 to 11, wherein step (a)
comprises:
(i) dividing the
MCSG feed stream into at least two portions, comprising a
first portion and a second portion;
(ii) cooling and partially liquefying the first portion of the MCSG feed
stream
in a first heat exchanger unit or set of units via indirect heat exchange with
a first
refrigerant, wherein the first heat exchanger unit or set of units is a coil-
wound heat
exchanger unit or set of units;
(iii) cooling and partially liquefying the second portion of the MCSG feed
stream in a second heat exchanger unit or set of units via indirect heat
exchange with
one or more process streams; and
(iv) combining the cooled and partially liquefied first portion and the
cooled
and partially liquefied second portion to form the partially liquefied MCSG
feed stream.
- 6 -
Date Recue/Date Received 2022-06-27
[0023]
Aspect 13: The method of Aspect 12, wherein the second heat exchanger unit or
set of units is a plate fin heat exchanger unit or set of units.
[0024]
Aspect 14: The method of Aspects 12 or 13, wherein in step (a)(iii) the one or
more process streams comprise one or more streams selected from the first
residue gas
stream, the second residue gas stream, and a portion of the LNG stream or
distillation column
bottoms liquid.
[0025]
Aspect 15: The method of any one of Aspects 12 to 14, wherein the first
refrigerant
is a refrigerant that vaporizes as it is warmed in the first heat exchanger
unit or set of units.
[0026]
Aspect 16: The method of any one of Aspects 12 to 15, wherein the method
further
comprises subcooling the LNG stream in the first heat exchanger unit or set of
units via indirect
heat exchange with the first refrigerant.
[0027]
Aspect 17: The method of any one of Aspects 12 to 16, wherein step (a)(ii)
comprises cooling and partially liquefying the first portion of the MCSG feed
stream in the first
heat exchanger unit or set of units via indirect heat exchange with one or
more streams of
cooled first refrigerant, wherein the first heat exchanger unit or set of
units is a coil-wound
heat exchanger unit or set of units, and wherein the one or more streams of
cooled first
refrigerant are produced by also cooling the first refrigerant in the first
heat exchanger unit or
set of units.
[0028]
Aspect 18: The method of any one of Aspects 1 to 11, wherein step (a)
comprises:
(i) cooling a first
refrigerant in a first heat exchanger unit or set of units to
produce a cooled first refrigerant, wherein the first heat exchanger unit or
set of units
is a coil-wound heat exchanger unit or set of units;
(ii)
cooling and partially liquefying the MCSG feed stream in a second heat
exchanger unit or set of units, via indirect heat exchange with one or more
streams of
the cooled first refrigerant and one or more process streams, to form the
partially
liquefied MCSG feed stream.
[0029]
Aspect 19: The method of Aspect 18, wherein the second heat exchanger unit or
set of units is a plate fin heat exchanger unit or set of units.
- 7 -
Date Recue/Date Received 2022-06-27
[0030]
Aspect 20: The method of Aspect 18 or 19, wherein in step (a)(ii) the one or
more
process streams comprise one or more of the first residue gas stream, the
second residue
gas stream, and a portion of the LNG stream or distillation column bottoms
liquid.
[0031]
Aspect 21: The method of any one of Aspects 18 to 20, wherein in step (a)(i)
the
first refrigerant is cooled in the first heat exchanger unit or set of units
via indirect heat
exchange with a portion of the cooled first refrigerant that is produced in
step (a)(i).
[0032]
Aspect 22: The method of any one of Aspects 18 to 21, wherein the method
further
comprises subcooling the LNG stream in the first heat exchanger unit or set of
units.
[0033]
Aspect 23: A method for producing liquefied natural gas (LNG) from methane
containing synthetic gas (MCSG), the method comprising:
(a)
cooling and partially liquefying a MCSG feed stream to produce a partially
liquefied MCSG feed stream by:
(i)
dividing the MCSG feed stream into at least two portions, comprising a
first portion and a second portion;
(ii) cooling and
partially liquefying the first portion in a first heat exchanger
unit or set of units via indirect heat exchange with a first refrigerant,
wherein the first
heat exchanger unit or set of units is a coil-wound heat exchanger unit or set
of units;
(iii) cooling and partially liquefying the second portion in a second heat
exchanger unit or set of units via indirect heat exchange with one or more
process
streams; and
(iv) combining the cooled and partially liquefied first portion and the
cooled
and partially liquefied second portion to form the partially liquefied MCSG
feed stream;
(b)
separating the partially liquefied MCSG feed stream into a LNG stream and
one or more residue gas streams.
[0034] Aspect 24: The method of Aspect 23, wherein in step (b) the
partially liquefied
MCSG feed stream is separated into the LNG stream and the one or more residue
gas
streams using one or more phase separators and/or one or more distillation
columns.
[0035]
Aspect 25: The method of Aspect 23 or 24, wherein the second heat exchanger
unit or set of units is a plate fin heat exchanger unit or set of units.
- 8 -
Date Recue/Date Received 2022-06-27
[0036]
Aspect 26: The method of any one of Aspects 23 to 25, wherein in step (a)(iii)
the
one or more process streams comprise one or more streams selected from the one
or more
of the residue gas streams, a portion of the LNG stream, or a portion of a
distillation column
bottoms liquid.
[0037] Aspect 27: The method of any one of Aspects 23 to 26, wherein the
first refrigerant
is a refrigerant that vaporizes as it is warmed in the first heat exchanger
unit or set of units.
[0038]
Aspect 28: The method of any one of Aspects 23 to 27, wherein the method
further
comprises subcooling the LNG stream in the first heat exchanger unit or set of
units via indirect
heat exchange with the first refrigerant.
[0039] Aspect 29: The method of any one of Aspects 23 to 28, wherein step
(a)(ii)
comprises cooling and partially liquefying the first portion of the MCSG feed
stream in the first
heat exchanger unit or set of units via indirect heat exchange with one or
more streams of
cooled first refrigerant, wherein the first heat exchanger unit or set of
units is a coil-wound
heat exchanger unit or set of units, and wherein the one or more streams of
cooled first
refrigerant are produced by also cooling the first refrigerant in the first
heat exchanger unit or
set of units.
[0040]
Aspect 30: A method for producing liquefied natural gas (LNG) from methane
containing synthetic gas (MCSG), the method comprising:
(a)
cooling and partially liquefying a MCSG feed stream to produce a partially
liquefied MCSG feed stream by:
(i) cooling a first refrigerant in a first heat exchanger unit or set of
units to
produce a cooled first refrigerant, wherein the first heat exchanger unit or
set of units
is a coil-wound heat exchanger unit or set of units;
(ii) cooling and partially liquefying the MCSG feed stream in a second heat
exchanger unit or set of units, via indirect heat exchange with one or more
streams of
the cooled first refrigerant and one or more process streams, to form the
partially
liquefied MCSG feed stream;
(b)
separating the partially liquefied MCSG feed stream into a LNG stream and
one or more residue gas streams.
- 9 -
Date Recue/Date Received 2022-06-27
[0041]
Aspect 31: The method of Aspect 30, wherein in step (b) the partially
liquefied
MCSG feed stream is separated into the LNG stream and the one or more residue
gas
streams using one or more phase separators and/or one or more distillation
columns.
[0042]
Aspect 32: The method of Aspect 30 or 31, wherein the second heat exchanger
unit or set of units is a plate fin heat exchanger unit or set of units.
[0043]
Aspect 33: The method of any one of Aspects 30 to 32, wherein in step (a)(ii)
the
one or more process streams comprise one or more of the first residue gas
stream, the second
residue gas stream, and a portion of the LNG stream or distillation column
bottoms liquid.
[0044]
Aspect 34: The method of any one of Aspects 30 to 33, wherein in step (a)(i)
the
first refrigerant is cooled in the first heat exchanger unit or set of units
via indirect heat
exchange with a portion of the cooled first refrigerant that is produced in
step (a)(i).
[0045]
Aspect 35: The method of any one of Aspects 30 to 34, wherein the method
further
comprises subcooling the LNG stream in the first heat exchanger unit or set of
units.
[0046]
Aspect 36: A system for producing liquefied natural gas (LNG) from methane
.. containing synthetic gas (MCSG), the system comprising:
one or more heat exchanger units for receiving, cooling and partially
liquefying a
MCSG feed stream to produce a partially liquefied MCSG feed stream;
a first phase separator and a second phase separator in fluid flow
communication with
the one or more heat exchanger units and arranged in series, with the second
phase separator
being in downstream fluid flow communication with the first phase separator,
for separating
the partially liquefied MCSG feed stream into at least three streams
comprising a liquid stream
and two vapor streams, the liquid stream forming a first feed stream, one of
the vapor streams
forming a second feed stream, and the other of the vapor streams forming a
first residue gas
stream; and
a distillation column having: a first inlet at a first location for receiving
the first feed
stream; a second inlet at second location for receiving the second feed
stream, the second
location being above the first location and having at least one separation
stage between the
first location and second location; an outlet at the bottom of the
distillation column for
withdrawal of an LNG stream formed of distillation column bottoms liquid; and
an outlet at the
- 10 -
Date Recue/Date Received 2022-06-27
top of the distillation column for withdrawal of a second residue gas stream
formed of
distillation column overhead vapor.
[0047]
Aspect 37: A system for producing liquefied natural gas (LNG) from methane
containing synthetic gas (MCSG), the system comprising:
a set of conduits for dividing a MCSG feed stream into at least two portions,
comprising
a first portion and a second portion;
a first heat exchanger unit or set of units for receiving the first portion
and cooling and
partially liquefying the first portion via indirect heat exchange with a first
refrigerant, wherein
the first heat exchanger unit or set of units is a coil-wound heat exchanger
unit or set of units;
a second heat exchanger unit or set of units for receiving the second portion
and
cooling and partially liquefying the second portion via indirect heat exchange
with one or more
process streams;
a set of conduits for receiving and combining the cooled and partially
liquefied first
portion and the cooled and partially liquefied second portion to form a
partially liquefied MCSG
feed stream; and
one or more phase separators and/or one or more distillation columns for
receiving
and separating the partially liquefied MCSG feed stream into a LNG stream and
one or more
residue gas streams.
[0048]
Aspect 38: A system for producing liquefied natural gas (LNG) from methane
containing synthetic gas (MCSG), the system comprising:
a first heat exchanger unit or set of units for cooling a first refrigerant to
produce a
cooled first refrigerant, wherein the first heat exchanger unit or set of
units is a coil-wound
heat exchanger unit or set of units;
a second heat exchanger unit or set of units for receiving one or more streams
of the
cooled first refrigerant from the first heat exchanger unit, for receiving one
or more process
streams, and for receiving an MCSG feed stream and cooling and partially
liquefying the
MCSG feed stream to form a partially liquefied MCSG feed stream via indirect
heat exchange
with the one or more streams of the cooled first refrigerant and the one or
more process
streams; and
- 11 -
Date Recue/Date Received 2022-06-27
one or more phase separators and/or one or more distillation columns for
receiving
and separating the partially liquefied MCSG feed stream into a LNG stream and
one or more
residue gas streams.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] Figure 1 is a schematic flow diagram depicting a method and
system for producing
LNG from MCSG according to one embodiment of the invention.
[0050] Figure 1A is a schematic flow diagram depicting a refrigeration
system suitable for
use in the method and system of Figure 1.
[0051] Figure 2 is a schematic flow diagram depicting a method and system
for producing
LNG from MCSG according to another embodiment of the invention.
[0052] Figure 3 is a schematic flow diagram depicting a method and
system for producing
LNG from MCSG according to another embodiment of the invention.
[0053] Figure 3A is a schematic flow diagram depicting a refrigeration
system suitable for
use in the method and system of Figure 3.
[0054] Figure 4 is a schematic flow diagram depicting a method and
system for producing
LNG from MCSG according to another embodiment of the invention.
DETAILED DESCRIPTION
[0055] Described herein are methods and systems for producing LNG from
MCSG.
[0056] As used herein and unless otherwise indicated, the articles "a"
and "an" mean one
or more when applied to any feature in embodiments of the present invention
described in the
specification and claims. The use of "a" and "an" does not limit the meaning
to a single feature
unless such a limit is specifically stated. The article "the" preceding
singular or plural nouns
or noun phrases denotes a particular specified feature or particular specified
features and
may have a singular or plural connotation depending upon the context in which
it is used.
[0057] Where letters are used herein to identify recited steps of a
method (e.g. (a), (b),
and (c)), these letters are used solely to aid in referring to the method
steps and are not
- 12 -
Date Recue/Date Received 2022-06-27
intended to indicate a specific order in which claimed steps are performed,
unless and only to
the extent that such order is specifically recited.
[0058] Where used herein to identify recited features of a method or
system, the terms
"first", "second", "third" and so on, are used solely to aid in referring to
and distinguishing
between the features in question, and are not intended to indicate any
specific order of the
features, unless and only to the extent that such order is specifically
recited.
[0059] As used herein, the term "methane containing synthetic gas", also
referred to
herein as "MCSG", refers to a gas comprising methane and components lighter
than methane
(i.e. components having a higher volatility and lower boiling point than
methane) such as in
particular hydrogen and/or carbon monoxide. The term as used herein includes
gasification
syngas product streams containing methane molecules and synthetic natural gas
streams
produced from methanation process which contain impurities such as hydrogen
and carbon
monoxide. In preferred embodiments, a methane-containing synthetic gas feed
stream may
comprise 10-60 mol% methane with the remaining content being a mixture of
carbon
monoxide and hydrogen, optionally with a small amounts of carbon dioxide,
water, and/or
other impurities.
[0060] As used herein, the term residue gas refers to a gas comprising
predominantly
components lighter than methane removed from the MCSG feed stream, such as in
particular
hydrogen and/or carbon monoxide. In preferred embodiments, a residue gas
stream may
comprise less than 10 mol% methane, and more preferably less than 2 mol%
methane, with
the remainder consisting or consisting essentially of components lighter than
methane, such
as for example a mixture of hydrogen and carbon monoxide, optionally with
small amounts of
other components such as nitrogen and/or argon.
[0061] As used herein, the term "liquefied natural gas" or "LNG" refers
to a liquefied gas
stream comprising predominantly methane, which preferably comprises at least
85 mole%,
more preferably at least 90 mole%, and most preferably at least about 95 mole%
of the feed
stream. An LNG stream may still contain small amounts of other components as
may have
been present in the MCSG feed stream and have not been removed by the process,
such as
small amounts of other components heavier (i.e. lower volatility and higher
boiling point) than
methane, such as carbon dioxide or hydrocarbons heavier than methane (e.g.
ethane,
- 13 -
Date Recue/Date Received 2022-06-27
propane, butane, pentanes) and/or small amounts of components lighter than
methane, such
as nitrogen, hydrogen or carbon monoxide.
[0062] As used herein, the term "distillation column" refers to a column
containing one or
more separation stages, composed of devices such as packing or trays, that
increase contact
and thus enhance mass transfer between upward rising vapor and downward
flowing liquid
flowing inside the column. In this way, the concentration of lighter (i.e.
higher volatility and
lower boiling point) components increases in the rising vapor that collects as
overhead vapor
at the top of the column, and the concentration of heavier (i.e. lower
volatility and higher boiling
point) components increases in the descending liquid that collects as bottoms
liquid at the
bottom of the column. The "top" of the distillation column refers to the part
of the column at
or above the top-most separation stage. The "bottom" of the column refers to
the part of the
column at or below the bottom-most separation stage. An "intermediate
location" of the
column refers to a location between the top and bottom of the column, between
two separation
stages.
[0063] As used herein, the term "phase separator" refers to a drum or other
form of vessel
in which a two phase stream can be introduced in order to separate the stream
into its
constituent vapor and liquid phases where the liquid and vapor streams exiting
the vessel are
in equilibrium. In contrast to a distillation column (in which the liquid and
vapor streams exiting
the column are not in equilibrium), a phase separator does not contain any
separation stages
(i.e. packing or trays) inside the vessel for bringing upward rising vapor and
downward flowing
liquid into contact.
[0064] As used herein, the term "fluid flow communication" refers to the
nature of
connectivity between two or more components that enables liquids, vapors,
and/or two-phase
mixtures to be transported between the components in a controlled fashion
(i.e., without
leakage) either directly or indirectly. Coupling two or more components such
that they are in
fluid flow communication with each other can involve any suitable method known
in the art,
such as with the use of welds, flanged conduits, gaskets, and bolts. Two or
more components
may also be coupled together via other components of the system that may
separate them,
for example, valves, gates, or other devices that may selectively restrict or
direct fluid flow.
- 14 -
Date Recue/Date Received 2022-06-27
[0065] Reference herein to a second device or component being in
"downstream" fluid
flow communication with a first device or component means that said second
device or
component is arranged so as to receive fluid, either directly or indirectly,
from said first device
or component.
[0066] As used herein, the term "indirect heat exchange" refers to heat
exchange between
two fluids where the two fluids are kept separate from each other by some form
of physical
barrier.
[0067] As used herein, the term "coil-wound heat exchanger unit" refers
to a heat
exchanger unit of the type known in the art, comprising one or more tube
bundles encased in
a shell casing. Each tube bundle comprises a plurality of tubes, the interior
of the tubes
defining one or more passages (also referred to as tube circuits) for passing
one or more fluid
streams through the heat exchanger unit, the interior of said tubes being
referred to herein as
the "tube side" of the heat exchanger unit. The space internal to the shell
casing and external
to the tubes defines a single passage for passing a fluid stream through the
heat exchanger
unit, said space internal to the shell casing and external to the tubes being
referred to herein
as the "shell side" of the heat exchanger unit. In this way, a fluid passing
through the shell
side of the heat exchanger can undergo indirect heat exchange with a fluid
passing through
the tube side of the heat exchanger. Where the coil-wound heat exchanger unit
is being used
to cool one or more 'hot' fluid streams via indirect heat exchange with a
'cold' refrigerant, the
cold refrigerant is almost always passed through the shell side of the heat
exchanger, as the
shell side provides much lower flow resistance and allows for a much greater
pressure drop
than the tube side, which makes passing the cold refrigerant through the shell
side much more
effective and efficient (the cold refrigerant typically being a vaporizing or
expanding fluid at a
relatively low pressure). Coil wound heat exchangers are a compact design of
heat exchanger
.. known for their robustness, safety, and heat transfer efficiency, and thus
have the benefit of
providing highly efficient levels of heat exchange relative to their
footprint. However, because
the shell side defines only a single passage through the heat exchanger, it is
not practicable
use more than one stream of cold refrigerant to provide cooling duty in a coil-
wound heat
exchanger if the mixing of said streams of refrigerant is not permitted.
[0068] Solely by way of example, various exemplary embodiments of the
invention will
now be described with reference to the Figures.
- 15 -
Date Recue/Date Received 2022-06-27
[0069] Referring now to Figure 1, a method and system for producing LNG
from MCSG
in accordance with a first embodiment of the invention is shown.
[0070] An MCSG feed stream 100, such as for example a syngas stream 100
comprising
a mixture of hydrogen, carbon monoxide, carbon dioxide, nitrogen, water,
methane, ethane
and other hydrocarbons, which is at ambient temperature and a high-pressure,
typically 20 to
80 bara, may first be routed to a pretreatment system 105. Depending on the
composition of
the MCSG feed stream, the pretreatment system can include an acid gas removal
unit for
removing hydrogen sulphide and carbon dioxide impurities, a dehydration unit
for removing
water, and a mercury removal unit for removing mercury. There may also be a
heavy
component removal step in which LPG (liquified petroleum gas) components,
freezable
pentane and heavier components, are removed. As such, the flowrate and
composition of the
MCSG feed stream 111 exiting the pretreatment section 105 may be significantly
different
than that of the MCSG feed stream 100 entering said pretreatment section 105,
although the
MCSG feed stream will still comprise methane and components lighter than
methane, in
particular hydrogen and carbon monoxide.
[0071] The MCSG feed stream 111 exiting the pretreatment section 105,
which is typically
at ambient temperature, is then divided into two streams, namely a first
stream 113 and a
second stream 115. The first stream 113, which preferably consists of a minor
portion of the
MCSG feed stream 111, such as between 10 and 40 percent and more preferably
between
20 and 30 percent of the flow of the MCSG feed stream 111, is sent to a first
heat exchanger
unit or set of units 114. The second stream 115, which consists of the
remainder of the flow
of the MCSG feed stream 111 and hence preferably consists of a major portion
of said stream,
is sent to a second heat exchanger unit or set of units 116. The second heat
exchanger unit
or set of units 116 may for example comprise a plate fin exchanger unit or a
plurality of plate
fin exchanger units arranged in parallel. The first and second streams 113 and
115 are cooled
and partially liquefied in, respectively, the first heat exchanger unit(s) 114
and second heat
exchanger unit(s) 116, forming respectively a first cooled and partially
liquefied stream 120
and a second cooled and partially liquefied stream 117 that are each at a
temperature of
between -130 C and -160 C and more preferably between -140 C and -150 C. The
first and
second cooled and partially liquefied streams 120, 117 are then combined (with
the pressure
of the second cooled and partially liquefied stream 117 first being regulated,
if necessary, and
- 16 -
Date Recue/Date Received 2022-06-27
via for example a pressure regulator valve 117A, to control the flow of said
stream 117) to
form a partially liquefied MCSG feed stream 130 that is then separated using a
first phase
separator 140 and a second phase separator 135 arranged in series, with the
second phase
separator being in downstream fluid flow communication with the first phase
separator.
[0072] More specifically, the partially liquefied MCSG feed stream 130 is
first introduced
into the first phase separator 140 which in this case is a flash drum in which
the partially
liquefied MCSG feed stream is flashed and separated into a liquid stream that
forms a first
feed stream 152, and a vapor stream 141. The vapor stream 141 is divided to
form a second
feed stream 143 (which preferably consists of between 60 and 90 percent or
more preferably
.. between 70 and 80 percent of the flow of vapor stream 141) and a third feed
stream 142
(which consists of the remainder of vapor stream 141, i.e. preferably between
10 and 40
percent and more preferably between 20 and 30 percent of the flow of said
stream). The
third feed stream 142 is further cooled and partially liquefied to form a
partially liquefied third
feed stream 133 at a temperature of between -170 C and -200 C and more
preferably
between -180 C and -190 C. The partially liquefied third feed stream 133 is
then introduced
into the second phase separator 135 which in this case is a flash drum in
which the partially
liquefied third feed stream is flashed and separated into a liquid stream that
forms a fourth
feed stream 150 and a vapor stream that forms a first residue gas stream 137.
[0073] The third feed stream 142 may be further cooled and partially
liquefied to form the
.. partially liquefied third feed stream 133 by passing the third feed stream
142 through a third
heat exchanger unit or set of units 131 as shown in Figure 1, which unit(s)
may for example
comprise a plate fin exchanger unit or a plurality of plate fin exchanger
units arranged in
parallel. Alternatively, the third heat exchanger unit(s) may be combined with
the second heat
exchanger unit(s) into a single unit, or set of units in parallel, with stream
115 being cooled in
a warmer section of said unit(s) and stream 142 being cooled in a colder
section of said unit(s).
[0074] The first feed stream 152 and fourth feed stream 150 are reduced
in pressure, for
example by passing stream 152 through J-T valve 152A and stream 150 through J-
T valve
150A, after which each of said streams will be two-phase. The second feed
stream 143 is
reduced in pressure, for example by expanding the stream in an expander 179,
after which
said second feed stream 151 may be vapor or two-phase. The expansion work from
expander
179 may for example be recovered by coupling the expander to a compressor
which
- 17 -
Date Recue/Date Received 2022-06-27
compresses feed or residue gas, or may for example be recovered in a
generator. The first
feed stream 152, second feed stream 151 and fourth feed stream 150 are then
each
introduced into different locations of a distillation column 145, as will be
further described
below, which distillation column 145 operates at a pressure of between 1.0 and
5.0 bara, and
more preferably between 1.5 and 3.5 bara.
[0075] The first feed stream 152 is introduced into the distillation
column 145 at a first
location that is above one or more separation stages of the column that are
represented in
Figure 1 by section 145C of the column, and that is below one or more
separation stages of
the column that are represented in Figure 1 by section 145B of the column. The
second feed
stream 151 is introduced into the distillation column at a second location
that is above the one
or more separation stages of the column that are represented by section 145B,
and that is
below one or more separation stages of the column that are represented in
Figure 1 by section
145A of the column. The fourth feed stream 150 is introduced into the
distillation column at a
third location that is at the top of the column, above the one or more
separation stages of the
column that are represented by section 145A, thereby providing a source of
reflux to the
column.
[0076] Reboiler duty for the distillation column 145 is provided warming
and thereby at
least partially vaporizing a stream of distillation column bottoms liquid 153
in the second heat
exchanger unit or set of units 116, via indirect heat exchange with the second
stream 115
.. (obtained from dividing the MCSG feed stream), thereby forming a boil-up
stream 154 (formed
of said partially vaporized distillation column bottoms liquid) that is
reintroduced into the
bottom of the distillation column.
[0077] An LNG stream 180 formed of distillation column bottoms liquid is
withdrawn from
the bottom of the distillation column 145 at a temperature between -130 C and -
160 C, and
more preferably between -140 C and -150 C, and is preferably increased in
pressure in pump
181 and sent (as stream 183) to and passed through the first heat exchanger
unit or set of
units 114 to be subcooled to form a subcooled LNG product stream 187 that can
be stored in
a LNG storage vessel on-site or transferred directly off-site (for example via
a pipeline or a
transport vessel). The LNG stream 180, 187 typically contains 1 mole % or less
nitrogen,
preferably less than 0.5 mole %, and preferably also has a carbon monoxide
content of 10
- 18 -
Date Recue/Date Received 2022-06-27
ppm or less. The percent of methane recovered in the LNG stream 180, 187 from
the MCSG
feed stream 111 can be higher than 95%.
[0078] A second residue gas stream 160 formed of distillation column
overhead vapor is
withdrawn from the top of the distillation column 145 at a temperature between
-170 C and -
200 C, and more preferably between -180 C and -190 C, and typically contains
greater than
95 and preferably greater than 98 mole % hydrogen and carbon monoxide.
[0079] The first residue gas stream 137 and second residue gas stream
160 are each
passed through and warmed in the third heat exchanger unit or set of units
131, via indirect
heat exchange with the third feed stream 142, and are then each (c.f. streams
138 and 161)
passed through and further warmed in the second heat exchanger unit or set of
units 116, via
indirect heat exchange with the second stream 115 obtained from dividing the
MCSG feed
stream (or in the alternative embodiment where the third heat exchanger
unit(s) are combined
with the second heat exchanger unit(s), the first residue gas stream 137 and
second residue
gas stream 160 are warmed in the colder section of said combined unit(s) and
then further
warmed in the warmer section of said combined unit(s)). The resulting warmed
second
residue gas stream 162 is then compressed and cooled in a compressor 163 and
aftercooler
165 before being mixed with the resulting warmed first residue gas stream 139
to formed a
combined residue gas stream 173. The residue gas stream 173 may be used for
fuel for the
plant or sent to downstream units for further purification, separation, and/or
chemical
synthesis. Optionally, some or all of stream 139 may be purified to make a
hydrogen product
and not combined with stream with residue gas stream 170.
[0080] The first heat exchanger unit or set of units 114 is a preferably
coil-wound unit or
set of units, as for example shown in Figure 1A. Any type of refrigeration
process as known
in the art for the liquefaction of natural gas (including synthetic or
substitute natural gases)
may be employed in the first heat exchanger unit or set of units 114, such as
a single mixed
refrigerant process; dual mixed refrigerant process; propane, ammonia or HFC
pre-cooled
mixed refrigerant process; reverse Brayton cycle using nitrogen, methane or
ethane; or
multiple fluid cascade cycle. However, in an exemplary embodiment a SMR
(single mixed
refrigerant) process may be used, such as the one depicted in Figure 1A.
- 19 -
Date Recue/Date Received 2022-06-27
[0081] As shown in Figure 1A, the coil-wound heat exchanger unit 114
comprises a warm
section comprising a warm tube bundle 114A and cold section comprising a cold
tube bundle
114B (the terms warm and cold being relative). The first stream 113 obtained
from dividing
the MCSG feed stream is passed through and cooled and partially liquefied in
the warm tube
bundle 114A to form the first cooled and partially liquefied stream 120. The
LNG steam 183
is passed through and subcooled in the cold tube bundle 114B to form the
subcooled LNG
product stream 187. Cooling duty is supplied to the warm and cold tube bundles
of the coil-
wound heat exchanger unit by vaporizing mixed refrigerant passing through the
shell side of
the heat exchanger unit. The SMR cycle depicted in Figure 1A that is used to
supply
vaporizing cold mixed refrigerant to the shell side of the heat exchanger unit
is one that is well
known in the art, and so for the sake of brevity will only cursorily be
described here. Very
briefly, warmed vaporized mixed refrigerant withdrawn from the shell side at
the bottom of the
heat exchanger unit is compressed, cooled and separated, in a compression
train comprising
one or more compressor stages 115A, 115B, aftercoolers and phase separators,
into one or
more MRL (mixed refrigerant liquid) streams, two being shown in the figure,
and one or more
MRV (mixed refrigerant vapor) streams, one being shown in the figure. The MRL
streams are
passed through and cooled in the warm tube bundle, expanded through J-T valves
and
combined and introduced into the shell side of the heat exchanger unit at the
top of the warm
bundle to provide vaporizing refrigerant flowing downwards through the shell
side around the
tubes of the warm tube bundle. The MRV stream is passed through and cooled and
at least
partially liquefied in the warm and cold tube bundles, expanded though a J-T
valve and
introduced into the shell side of the heat exchange unit at the top of the
cold bundle to provide
vaporizing refrigerant flowing downwards through the shell side around the
tubes of the cold
and warm tube bundles.
[0082] The method and system of Figure 1 produces a high purity methane-
rich LNG
product with a high methane recovery. It requires only a single distillation
column and
recompression of only part of the residue gas that is produced (i.e. only the
residue gas
contained in the second residue gas stream), hence reducing the capital and
operating costs
and footprint of the system as compared to systems requiring multiple
distillation columns,
recompression of all of the residue gas produced, and a compressor capable of
compressing
all of the residue gas produced. It allows use of a coil-wound heat exchanger
unit, thereby
- 20 -
Date Recue/Date Received 2022-06-27
also taking advantage of the benefits provided by such units in terms of their
compact design,
robustness, safety, and heat transfer efficiency, further reducing the
footprint and enhancing
the efficiency of the system and process. It also avoids use of a two-phase
refrigerant in the
second and third heat exchanger units, which as discussed may for example be
plate fin
exchanger units, thereby avoiding any operational difficulties that may result
from use of such
a refrigerant in such types of heat exchanger.
[0083] Figure 2 shows a method and system for producing LNG from MCSG in
accordance with a second embodiment of the invention. The embodiment depicted
in Figure
2 differs from that shown in Figure 1 as regards the manner in which partially
liquefied MCSG
feed stream is separated by the first and second phase separators, and as
regards the manner
in which reflux is provided to the distillation column.
[0084] An MCSG feed stream 200, such as for example a syngas stream 200
comprising
a mixture of hydrogen, carbon monoxide, carbon dioxide, nitrogen, water,
methane, ethane
and other hydrocarbons, which is at ambient temperature and a high-pressure,
typically 20 to
80 bara, may first be routed to a pretreatment system 205. Depending on the
composition of
the MCSG feed stream, the pretreatment system can include an Acid Gas Removal
Unit for
removing hydrogen sulphide and carbon dioxide impurities, a Dehydration Unit
for removing
water, and a Mercury Removal Unit for removing mercury. There may also be a
heavy
component removal step in which LPG (liquified petroleum gas) components,
freezable
pentane and heavier components, are removed. As such, the flowrate and
composition of the
MCSG feed stream 211 exiting the pretreatment section 205 may be significantly
different
than that of the MCSG feed stream 200 entering said pretreatment section 205,
although the
MCSG feed stream will still comprise methane and components lighter than
methane, in
particular hydrogen and carbon monoxide.
[0085] The MCSG feed stream 211 exiting the pretreatment section 205, which
is typically
at ambient temperature, is then divided into two streams, namely a first
stream 213 and a
second stream 215. The first stream 213, which preferably consists of a minor
portion of the
MCSG feed stream 211, such as between 10 and 40 percent and more preferably
between
20 and 30 percent of the flow of the MCSG feed stream 211, is sent to a first
heat exchanger
unit or set of units 214. The second stream 215, which consists of the
remainder of the flow
of the MCSG feed stream 211 and hence preferably consists of a major portion
of said stream,
- 21 -
Date Recue/Date Received 2022-06-27
is sent to a second heat exchanger unit or set of units 216. The second heat
exchanger unit
or set of units 216 may for example comprise a plate fin exchanger unit or a
plurality of plate
fin exchanger units arranged in parallel. The first and second streams 213 and
215 are cooled
and partially liquefied in, respectively, the first heat exchanger unit(s) 214
and second heat
exchanger unit(s) 216, forming respectively a first cooled and partially
liquefied stream 220
and a second cooled and partially liquefied stream 217 that are each at a
temperature of
between -120 C and -150 C and more preferably between -130 C and -140 C. The
first and
second cooled and partially liquefied streams 220, 217 are then combined (with
the pressure
of the second cooled and partially liquefied stream 217 first being regulated,
if necessary, and
via for example a valve 217A, to control the flow of stream 217) to form a
partially liquefied
MCSG feed stream 230.
[0086] The partially liquefied MCSG feed stream 230 is then further
cooled (and further
partially liquefied) in a third heat exchanger unit or set of units 231 to
form a partially liquefied
MCSG feed stream 233 at a temperature of between -155 C and -185 C and more
preferably
between -165 C and -175 C. The third heat exchanger unit or set of units 231
may for example
comprise a plate fin exchanger unit or a plurality of plate fin exchanger
units arranged in
parallel. In an alternative embodiment (not depicted), the third heat
exchanger unit(s) may be
combined with the second heat exchanger unit(s) into a single unit, or set of
units in parallel,
with stream 215 being cooled in a warmer section of said unit(s) and stream
230 being cooled
in a colder section of said unit(s).
[0087] The partially liquefied MCSG feed stream 233 is then separated
using a first phase
separator 235 and a second phase separator 240 arranged in series, with the
second phase
separator being in downstream fluid flow communication with the first phase
separator. More
specifically, the partially liquefied MCSG stream 233 is first introduced into
the first phase
separator 235, which in this case is a flash drum, in which the partially
liquefied MCSG feed
stream is flashed and separated into a liquid stream that forms a third feed
stream 236, and
a vapor stream that forms a first residue gas stream 237. The third feed
stream 236 is reduced
in pressure and partially vaporized, for example by passing the stream through
J-T valve
237A, after which said stream is two-phase, after which the partially
vaporized two-phase third
feed stream is then introduced into the second phase separator 240, which in
this case is a
flash drum, in which the partially liquefied third feed stream is flashed and
separated into a
- 22 -
Date Recue/Date Received 2022-06-27
liquid stream that forms a first feed stream 242 and a vapor stream that forms
a second feed
stream 251.
[0088] The first feed stream 242, the flow which is controlled by valve
242A in order to
control the liquid level in the second phase separator 240, is passed through
and warmed in
the third heat exchanger unit or set of units 231, via indirect heat exchange
with the partially
liquefied MCSG feed stream 230, after which said stream will be two-phase (or
in the
alternative embodiment where the third heat exchanger unit(s) are combined
with the second
heat exchanger unit(s), the third feed stream 242 is warmed in the colder
section of said
combined unit(s)). The first feed stream 252 and second feed stream 251 are
then each
introduced into different locations of a distillation column 245, as will be
further described
below, which distillation column 245 operates at a pressure of between 3.0 and
7.0 bara, and
more preferably between 4.5 and 5.5 bara.
[0089] The first feed stream 252 is introduced into the distillation
column 245 at a first
location that is above one or more separation stages of the column that are
represented in
Figure 2 by section 245C of the column, and that is below one or more
separation stages of
the column that are represented in Figure 1 by section 245B of the column. The
second feed
stream 251 is introduced into the distillation column at a second location
that is above the one
or more separation stages of the column that are represented by section 245B,
and that is
below one or more separation stages of the column that are represented in
Figure 2 by section
245A of the column.
[0090] Reboiler duty for the distillation column 245 is provided
warming and thereby at
least partially vaporizing a stream of distillation column bottoms liquid 253
in the second heat
exchanger unit or set of units 116, via indirect heat exchange with the second
stream 215
(obtained from dividing the MCSG feed stream), thereby forming a boil-up
stream 254 (formed
of said partially vaporized distillation column bottoms liquid) that is
reintroduced into the
bottom of the distillation column.
[0091] An LNG stream 280 formed of distillation column bottoms liquid
is withdrawn from
the bottom of the distillation column 245 at a temperature between -125 C and -
155 C, and
more preferably between -135 C and -145 C, and is preferably increased in
pressure in pump
181 and sent (as stream 283) to and passed through the first heat exchanger
unit or set of
- 23 -
Date Recue/Date Received 2022-06-27
units 214 to be subcooled to form a subcooled LNG product stream 287 that can
be stored in
a LNG storage vessel on-site or transferred directly off-site (for example via
a pipeline or a
transport vessel). The LNG stream 280, 287 typically contains 1 mole % or less
nitrogen,
preferably less than 0.5 mole %, and preferably also has a carbon monoxide
content of 10
ppm or less. The percent of methane recovered in the LNG stream 280, 287 from
the MCSG
feed stream 211 can be higher than 95%.
[0092] A second residue gas stream 260 formed of distillation column
overhead vapor is
withdrawn from the top of the distillation column 245 at a temperature between
-160 C and -
190 C, and more preferably between -170 C and -180 C, and typically contains
greater than
95 and preferably greater than 98 mole % hydrogen and carbon monoxide.
[0093] The first residue gas stream 237 and second residue gas stream
260 are each
passed through and warmed in the third heat exchanger unit or set of units 231
and are then
each (c.f. streams 238 and 261) passed through and further warmed in the
second heat
exchanger unit or set of units 216 resulting in a warmed first residue gas
stream 239 and
warmed second residue gas stream 262 (or in the alternative embodiment where
the third
heat exchanger unit(s) are combined with the second heat exchanger unit(s),
the first residue
gas stream 237 and second residue gas stream 260 are warmed in the colder
section of said
combined unit(s) and then further warmed in the warmer section of said
combined unit(s)).
The warmed second residue gas stream 262 is then compressed and cooled in a
compressor
263 and aftercooler 265 to form a compressed second residue gas stream 270
that is then
divided into two portions 271, 275.
[0094] A first portion 271 of the compressed second residue gas stream,
which preferably
consists of a minor portion of the compressed second residue gas stream 270,
such as
between 10% and 30% and more preferably between 15% and 25% of the flow of
said stream,
is mixed with the warmed first residue gas stream 239 to form a combined
residue gas stream
273. The residue gas stream 273 may be used for fuel for the plant or sent to
downstream
units for further purification, separation, and/or chemical synthesis.
Optionally, some or all of
stream 239 may be purified to make a hydrogen product and not combined with
residue gas
stream 271.
- 24 -
Date Recue/Date Received 2022-06-27
[0095] A second portion 275 of the compressed second residue gas stream,
which
consists of the remainder of the flow of the compressed second residue gas
stream 270 and
hence preferably consists of a major portion of said stream, is passed through
and cooled in
the second heat exchanger unit or set of units 216 (or in the alternative
embodiment where
the third heat exchanger unit(s) are combined with the second heat exchanger
unit(s), the
second portion 275 is cooled in the warmer section of said combined unit(s))
to form a cooled
stream 277 at temperature between -120 C and -150 C and more preferably
between -130 C
and -140 C. Said cooled stream 277 is then expanded in an expander 279 to form
an at least
partially liquefied reflux stream 250, having a temperature of between -160 C
and -190 C and
more preferably between -170 C and -180 C, that is introduced into the
distillation column
245 at a third location that is at the top of the column, above the one or
more separation
stages of the column that are represented by section 245A, thereby providing a
source of
reflux to the column. The expansion work from expander 279 may for example be
recovered
by coupling the expander to a compressor which compresses feed or residue gas,
or may for
example be recovered in a generator.
[0096] The first heat exchanger unit or set of units 214 is a preferably
coil-wound unit or
set of units, as for example shown in Figure 1A. Any type of refrigeration
process as known
in the art for the liquefaction of natural gas (including synthetic or
substitute natural gases)
may be employed in the first heat exchanger unit or set of units 214, such as
a single mixed
refrigerant process; dual mixed refrigerant process; propane, ammonia or HFC
pre-cooled
mixed refrigerant process; reverse Brayton cycle using nitrogen, methane or
ethane; or
multiple fluid cascade cycle. However, in an exemplary embodiment a SMR
(single mixed
refrigerant) process may be used, such as the one depicted in Figure 1A and
described above.
[0097] The method and system of Figure 2 has the same advantages and
benefits as the
method and system of Figure 1 described above. As compared to the embodiment
shown in
Figure 1, the embodiment shown in Figure 2 can achieve even higher methane
recovery by
employing a reflux with very low methane content, thus further improving the
methane
recovery of the process. However, the embodiment shown in Figure 1 does have a
better
specific power as compared to the embodiment shown in Figure 2.
[0098] Figure 3 shows a method and system for producing LNG from MCSG in
accordance with a third embodiment of the invention. In Figure 3, features
that are shared
- 25 -
Date Recue/Date Received 2022-06-27
with the first embodiment depicted in Figure 1 have been assigned the same
reference
numerals increased by a factor of 200. Thus, for example, the partially
liquefied MCSG feed
stream 330 in Figure 3 corresponds to the partially liquefied MCSG feed stream
130 in Figure
1, and the distillation column 345 in Figure 3 corresponds to the distillation
column 145 shown
in Figure 1. Unless a feature of Figure 3 is specifically described as being
different from the
corresponding feature of Figure 1, that feature can be assumed to have the
same structure
and function as the corresponding feature in Figure 1 described above.
Moreover, if that
feature does not have a different structure or function, it may not be
specifically referred to in
the further description of Figure 3 below.
[0099] The embodiment depicted in Figure 3 differs from that depicted in
Figure 1 as
regards the manner in which the MCSG feed stream is cooled to form the
partially liquefied
MCSG feed stream, and as regards the manner in which the first heat exchanger
unit or set
of units is used, the first heat exchanger unit or set of units being used to
supply refrigerant
and thereby additional refrigeration to the third heat exchanger unit or set
of units and second
heat exchanger unit or set of units.
[0100] More specifically, in Figure 3 the whole of the MCSG feed stream
311 exiting the
pretreatment section 305 is sent to and passed through the second heat
exchanger unit or set
of units 316, in which the MCSG feed stream 311 is cooled and partially
liquefied to form the
partially liquefied MCSG feed stream 330, at a temperature of between -130 C
and -160 C
and more preferably between -140 C and -150 C, that is then separated using
the first phase
separator 340 and second phase separator 335 arranged in series (as described
above in
relation to Figure 1). As described above in relation to Figure 1, the second
heat exchanger
unit or set of units 316 may for example comprise a plate fin exchanger unit
or a plurality of
plate fin exchanger units arranged in parallel.
[0101] The first heat exchanger unit or set of units 314 is not used to
receive and cool any
part of the MCSG feed stream. Instead, in the arrangement shown in Figure 3
the first heat
exchanger unit or set of units 314 is used to cool a first refrigerant and
produce a stream of
cooled first refrigerant 390 that is withdrawn from the first heat exchanger
unit or set of units
314 and passed through and warmed in the third heat exchanger unit or set of
units 331, via
indirect heat exchange with the third feed stream 342, thereby providing
additional
refrigeration (alongside the first residue gas stream 337 and second residue
gas stream 360)
- 26 -
Date Recue/Date Received 2022-06-27
to said unit(s). The resulting stream of first refrigerant 392 exiting the
third heat exchanger
unit or set of units 331 is then passed through and further warmed in the
second heat
exchanger unit or set of units 316, via indirect heat exchange with the MCSG
feed stream
311, thereby providing additional refrigeration (alongside the first residue
gas stream 338,
second residue gas stream 361, and stream of distillation column bottoms
liquid 353) to said
unit(s). The resulting warmed stream of first refrigerant 395 is then returned
to the first heat
exchanger unit or set of units 314 to once again be cooled in said unit(s). In
those alternative
embodiments where the third heat exchanger unit(s) are combined with the
second heat
exchanger unit(s), the stream of cooled first refrigerant 390 is instead
warmed in the colder
section of said combined unit(s) and then further warmed in the warmer section
of said
combined unit(s).
[0102] The first heat exchanger unit or set of units 314 is a preferably
coil-wound unit or
set of units, as for example shown in Figure 3A. Any type of refrigeration
process as known
in the art for the liquefaction of natural gas (including synthetic or
substitute natural gases)
may be employed in the first heat exchanger unit or set of units 314, such as
a single mixed
refrigerant process; dual mixed refrigerant process; propane, ammonia or HFC
pre-cooled
mixed refrigerant process; reverse Brayton cycle using nitrogen, methane or
ethane; or
multiple fluid cascade cycle. However, in an exemplary embodiment a SMR
(single mixed
refrigerant) process may be used, such as the one depicted in Figure 3A, in
which the first
refrigerant is a mixed refrigerant.
[0103] As shown in Figure 3A, the coil-wound heat exchanger unit 314
comprises a warm
section comprising a warm tube bundle 314A and cold section comprising a cold
tube bundle
314B (the terms warm and cold being relative). The LNG steam 383 is passed
through and
subcooled in the cold tube bundle 114B to form the subcooled LNG product
stream 387.
Cooling duty is supplied to the warm and cold tube bundles of the coil-wound
heat exchanger
unit by cooled first refrigerant that passes through and warms and vaporizes
in the shell side
of the heat exchanger unit. The SMR cycle depicted in Figure 3A that is used
to cool the first
refrigerant is one that is well known in the art, and so for the sake of
brevity will only cursorily
be described here. Very briefly, warmed vaporized first refrigerant withdrawn
from the shell
side at the bottom of the heat exchanger unit is combined with the stream of
warmed
vaporized first refrigerant 395 (returning from the first heat exchanger unit
or set of units 314)
- 27 -
Date Recue/Date Received 2022-06-27
and compressed, cooled and separated, in a compression train comprising one or
more
compressors, aftercoolers and phase separators, into one or more MRL (mixed
refrigerant
liquid) streams, two being shown in the figure, and one or more MRV (mixed
refrigerant vapor)
streams, one being shown in the figure. The MRL streams are passed through and
cooled in
the warm tube bundle, expanded through J-T valves and combined and introduced
into the
shell side of the heat exchanger unit at the top of the warm bundle to provide
vaporizing first
refrigerant flowing downwards through the shell side around the tubes of the
warm tube
bundle.
[0104] The MRV stream is passed through and cooled and at least
partially liquefied in
the warm and cold tube bundles, to form a stream of cooled first refrigerant
that is withdrawn
from the top of the cold tube bundle, and that is expanded and divided to form
the stream of
cooled first refrigerant 390 (that, as described above, is warmed and, in this
case, vaporized
in the third heat exchanger unit or set of units 331 and second heat exchanger
unit or set of
units 316) and a stream of cooled first refrigerant that is introduced into
the shell side of the
first heat exchanger unit 314 at the top of the cold bundle to provide
vaporizing first refrigerant
flowing downwards through the shell side around the tubes of the cold and warm
tube bundles.
The stream of cooled first refrigerant that is withdrawn from the top of the
cold tube bundle
may be expanded, for example by passing the stream through a J-T valve, and
then divided
to form the stream of cooled first refrigerant 390 and stream of cooled first
refrigerant that is
introduced into the shell side of the first heat exchanger unit 314 at the top
of the cold bundle,
as shown in Figure 3A. Alternatively, the stream of cooled first refrigerant
that is withdrawn
from the top of the cold tube bundle may first be divided, and then the
resulting divided streams
expanded separately (for example using separate J-T valves).
[0105] The method and system of Figure 3 has similar advantages and
benefits to the
method and system of Figure 1 described above. As compared to the embodiment
shown in
Figure 1, the embodiment shown in Figure 3 avoids these need to divide and
distribute the
MCSG feed stream between the first and second heat exchanger units, but has
the potential
disadvantage of requiring use of a two-phase refrigerant in the second and/or
third heat
exchanger unit (i.e. where the first refrigerant used in the second and/or
third heat exchanger
unit is two-phase).
- 28 -
Date Recue/Date Received 2022-06-27
[0106] Figure 4 shows a method and system for producing LNG from MCSG in
accordance with a fourth embodiment of the invention. In Figure 4, features
that are shared
with the second embodiment depicted in Figure 2 have been assigned the same
reference
numerals increased by a factor of 200. Thus, for example, the partially
liquefied MCSG feed
stream 430 in Figure 4 corresponds to the partially liquefied MCSG feed stream
230 in Figure
2, and the distillation column 445 in Figure 4 corresponds to the distillation
column 445 in
Figure 1. Unless a feature of Figure 4 is specifically described as being
different from the
corresponding feature of Figure 2, that feature can be assumed to have the
same structure
and function as the corresponding feature in Figure 2 described above.
Moreover, if that
feature does not have a different structure or function, it may not be
specifically referred to in
the further description of Figure 4 below.
[0107] The embodiment depicted in Figure 4 differs from that depicted in
Figure 2 as
regards the manner in which the MCSG feed stream is cooled to form the
partially liquefied
MCSG feed stream, and as regards the manner in which the first heat exchanger
unit or set
of units is used, the first heat exchanger unit or set of units being used to
supply refrigerant
and thereby additional refrigeration to the third heat exchanger unit or set
of units and second
heat exchanger unit or set of units.
[0108] More specifically, in Figure 4 the whole of the MCSG feed stream
411 exiting the
pretreatment section 405 is sent to and passed through the second heat
exchanger unit or set
of units 416, in which the MCSG feed stream 411 is cooled and partially
liquefied to form the
partially liquefied MCSG feed stream 430, at a temperature of between -120 C
and -150 C
and more preferably between -130 C and -140 C, that is then separated using
the first phase
separator 435 and second phase separator 440 arranged in series (as described
above in
relation to Figure 2). As described above in relation to Figure 2, the second
heat exchanger
unit or set of units 416 may for example comprise a plate fin exchanger unit
or a plurality of
plate fin exchanger units arranged in parallel.
[0109] The first heat exchanger unit or set of units 414 is not used to
receive and cool any
part of the MCSG feed stream. Instead, in the arrangement shown in Figure 4
the first heat
exchanger unit or set of units 414 is used to cool a first refrigerant and
produce a stream of
cooled first refrigerant 490 that is withdrawn from the first heat exchanger
unit or set of units
414 and passed through and warmed in the third heat exchanger unit or set of
units 431, via
- 29 -
Date Recue/Date Received 2022-06-27
indirect heat exchange with the partially liquefied MCSG feed stream 430,
thereby providing
additional refrigeration (alongside the first residue gas stream 437, second
residue gas stream
460 and first feed stream 442) to said unit(s). The resulting stream of first
refrigerant 492
exiting the third heat exchanger unit or set of units 431 is then passed
through and further
warmed in the second heat exchanger unit or set of units 416, via indirect
heat exchange with
the MCSG feed stream 411, thereby providing additional refrigeration
(alongside the first
residue gas stream 438, second residue gas stream 461, and stream of
distillation column
bottoms liquid 453) to said unit(s). The resulting warmed stream of first
refrigerant 495 is then
returned to the first heat exchanger unit or set of units 414 to once again be
cooled in said
unit(s). In those alternative embodiments where the third heat exchanger
unit(s) are combined
with the second heat exchanger unit(s), the stream of cooled first refrigerant
490 is instead
warmed in the colder section of said combined unit(s) and then further warmed
in the warmer
section of said combined unit(s).
[0110] The first heat exchanger unit or set of units 414 is a preferably
coil-wound unit or
set of units, as for example shown in Figure 3A. Any type of refrigeration
process as known
in the art for the liquefaction of natural gas (including synthetic or
substitute natural gases)
may be employed in the first heat exchanger unit or set of units 414, such as
a single mixed
refrigerant process; dual mixed refrigerant process; propane, ammonia or HFC
pre-cooled
mixed refrigerant process; reverse Brayton cycle using nitrogen, methane or
ethane; or
multiple fluid cascade cycle. However, in an exemplary embodiment a SMR
(single mixed
refrigerant) process may be used, such as the one depicted in Figure 3A and
described above.
[0111] The method and system of Figure 4 has the same advantages and
benefits as the
method and system of Figure 3 described above. As compared to the embodiment
shown in
Figure 3, the embodiment shown in Figure 4 can achieve even higher methane
recovery by
employing a reflux with very low methane content, thus further improving the
methane
recovery of the process. However, the embodiment shown in Figure 3 does have a
better
specific power as compared to the embodiment shown in Figure 4.
- 30 -
Date Recue/Date Received 2022-06-27
EXAMPLE 1
[0112] In this example, a method and system for producing liquefied
natural gas (LNG)
from a methane-containing synthetic gas (MCSG) as depicted in Figure 1 was
simulated,
using Aspen version 10. Table 1 below provides stream data from the
simulation. In this
example, the residue gas compressor 163 has four stages with an approximate
break
horsepower of 61.8 MW, the mixed refrigerant compressor 115 A and 115B has an
approximate break horsepower of 30.3 MW, the expander 179 extracts 10.5 MW of
work and
the process has a methane recovery of 95%.
- 31 -
Date Recue/Date Received 2022-06-27
ED
co
EP
7:] Stream # 111 113 115 117 120 141
142 143 133 137 138 139 150 a)
CD
K1
C Temperature C 30.0 30.0 30.0 -143.2 -144.9
-143.9 -143.9 -143.9 -183 6 -183.6 -146.9 26.1 -
183.6 o-
.
CD
CT
C) Pressure bara 37.0 37.0 37.0 36.8 35.6
35.6 35.6 35.6 35.4 35.4 35.1 34.9 35.4
SD
CD Vapor Fraction - 1.00 1.00 1.00 0.89
0.87 1.00 1.00 1.00 0.67 1.00 1.00 1.00 0.00 I
CD Flow kgnnolIhr 36,862 9,061 27,802 27,802
9,061 32,645 10,524 22,120 10,524 7,036 7,036 7,036
3,488 a)
0
CD
a)
R."
=
CD
a
a Composition mol%
Iv K
o H2 56.47 56.47 ___ 56.47 56.47
56.47 63.27 __ 63.27 63.27 63.27 92.04 92.04 92.04 5.24
a)
Iv
,
,.) CO 24.21 24.21 24.21 24.21
24.21 24.23 24.23 24.23 24.23 7.53 7.53 7.53 57.92
g,)
c.
0) CD _________________ 0.01 0.01 0.01 0.01 0.01
0 00 0.00 0.00 __ 0 00 0.00 0.00 0.00 0 00 fa)
K) .
. . -
--4 N2 0.13 0.13 0.13 0.13 0.13
0.14 0.14 0.14 0.14 0.06 0.06 0.06 0.29
_
AR 0.08 0.08 0.08 0.08 0.08
0.07 0.07 0.07 0.07 0.02 0.02 0.02 0.19 fa)
=
Cl 18.89 18.89 18.89 18.89
18.89 12.27 12.27 12.27 12.27 0.35 0.35 0.35 36.31
(D
EL 0.21 0.21 0.21 0.21 0.21
0.01 0.01 0.01 0.01 0.00 0.00 0.00 0.04
Total 100.00 100.00 100.00 100.00
100.00 100 00 __ 100.00 100.00 100 00 100.00 100.00
100.00 100 00
.
. .
\
oa
IN) Stream # 151 152 153 154 160 161
162 164 170 173 180 183 187
Temperature C -183.6 -143.9 -145.6 -145.5 -
186.6 -146.9 26.1 109.8 30.0 29.0 -145.5 -144.9 -
159.4
Pressure bara 3.0 35.6 3.1 3.1 3.0 2.7
2.5 35.4 34.9 34.9 3.1 15.2 11.7
Vapor Fraction - 0.87 0.00 0.00 0.28 1.00
1 00 1.00 1.00 1 00 1.00 0.00 0.00 0 00
.
. .
Flow kgmollhr 22,120 4,218 9,351 9,351
23,129 23,129 23,129 23,129 23,129 30,166 6,697 6,697
6,697
Composition mol%
H2 63.27 3.86 0.00 0.00 62.00
62.00 62.00 62.00 62.00 69.01 0.00 0.00 0.00
CO 24.23 24.03 0.00 0.00 36.29
36 29 36.29 36.29 36 29 29.58 0.00 0.00 0 00
.
. .
CD 0.00 0.08 0.04 0.04 0.00
0.00 0.00 0.00 0.00 0.00 0.06 0.06 0.06
N2 0.14 0.10 0.00 0.00 0.19
0.19 0.19 0.19 0.19 0.16 0.00 0.00 0.00
AR 0.07 0.10 0.03 0.03 0.11
0.11 0.11 0.11 0.11 0.09 0.01 0.01 0.01
Cl 12.27 70.14 99.10 99.10 1.40
1.40 1.40 1.40 1.40 1.15 98.79 98.79 98.79
EL 0.01 1.70 0.83 0.83 0.00
0.00 0.00 0.00 0.00 0.00 1.14 1.14 1.14
Total 100.00 100.00 100.00 100.00
100.00 100.00 100.00 100.00 100.00 100.00 100.00 100.00
100.00
EXAMPLE 2
[0113]
In this example, a method and system for producing liquefied natural gas (LNG)
from a methane containing synthetic gas (MCSG) as depicted in Figure 2 was
simulated,
using Aspen version 10. Table 2 below provides stream data from the
simulation.
- 33 -
Date Recue/Date Received 2022-06-27
Table 2: Heat and Material Balance
Stream 1 ____________________ 2111 113 219 ill -IQT-130 13¨ri39
141 294' 191 19'
Temperature 'C 10 308 308 111 .131 2 .135 1 =18
.1118 .1118 .139 1 25 5 .1747 Ali .141 1554.
Pressure bara 31.0 370 370 35 8 35 5 35 5 314 354
354 35 1 340 52 47 82 1.3
Vapor Fraction 01 800 004 010 181 C: 111
CI) 083 " CO 0.91
Flow ligmol lir 35 i2 11 101 25 111 26111 11.201 35 852
36,1E 13: 222 23641 23 611 23.611 11 982 25 592 1.248
11
i
_______________________________________________________ 1
Composition mol%
5647Ill 5647 5647 5647 5611 5611 5647 477 3130
0131 8639 037' 936 4726 1 31
CU 2.1.11 22 2121 2121 2* 2121 2411 1111
1385 103 1305 1312 39.11 482 131
CU Oil 081 081 1.01 Ul 0.11' NI 031
0 C: 1.N C ii U i'1.13'
112 813 813 013 013 0013 0.13 313 020 ON
009309 819 041 035 019
AR 088 08 008 008 008 0.08 ON 0.18 003
003 003 018 031 011 0.18
Cl 1889 1889 181 109 10,09 lb 1889 N13. 1.42 1421 142 5489 018
407 54.30
EL 1 21 0 21 0 21 : 21 1,1 58 000 ON'
0.01 0 61 1 00 00u 364
.
Total MN MN IN 11 MA 1 0 i1 N ION INN 11100 INN
'211: 10030
I I I I
Steam l 153 154 NI 131 131 134 110 111 113
115 111 130 131 131'
Temperature 'C 1379. 1378. =1763 19 1 25 5 011 3: 2
888 25 9 30 0 ,135 .131 8 .:73 ."59
Pressure bra 19 19 17 =:3 121 391 333 339 313
339 33.1 19 13:2 "7
Vapor Frain 000 823 183 001 100I 1 11 118 113 1C:
100 101 888 C:: 001
Flow Oft 9111 0011
K.211 34217 411 34211 31,211 8828 N.188 E892 E892 8897 8.8Fbl
Compsilk mol%
Ill 0000:0988965 356
9669669666901966966000E000
CU 3: 0 03 3111 39 0011 3944 8911 3944
1913 39.14 8941 000 ON 000
CO Oil C:1 38: 333 000, 11,001 000 0.00
064 103 ON 005 064. 005.
_
11111 0.10' 0 311 041 111 011 041 041 016
041 111 000 ON 1 CO
AR ME 081 031
001 2.31 031 1.31 0009 031 831 000 000 000
Cl 9911
99120180100801801018 003 01019880 HE 9880
El 002 082 OE 000 000 000 000 ON 000
000 000 111 111 111
Total ICI'NC a
1:00: MFJ IN Mi] ME a 64001 183 MN MN
[0114] The method and system in this Example uses a heat pump (expander 279)
to allow
extremely high product recovery. It produces a high purity reflux with very
low methane
- 34 -
Date Recue/Date Received 2022-06-27
content, thus improving the methane recovery of the process as compared to the
process of
Example 1. However, the process of Example 1 has a better specific power
compared to the
process of Example 2, 848.5 vs 922.6 kW-hr/tonne.
[0115] It will be appreciated that the invention is not restricted to the
details described
above with reference to the preferred embodiments but that numerous
modifications and
variations can be made without departing from the spirit or scope of the
invention as defined
in the following claims.
- 35 -
Date Recue/Date Received 2022-06-27
