Note: Descriptions are shown in the official language in which they were submitted.
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MIXED REFRIGERANT LIQUEFACTION SYSTEM AND METHOD
WITH PRE-COOLING
CLAIM OF PRIORITY
100011 This application claims the benefit of U.S. Provisional Application No.
62/660,518,
filed April 20,2018, the contents of which are hereby incorporated by
reference.
FIELD OF THE DISCLOSURE
100021 The present invention relates generally to systems and methods for
cooling or
liquefying gases and, more particularly, to a mixed refrigerant liquefaction
system and
method that uses cold vapor separation to fractionate high pressure mixed
refrigerant vapor
into liquid and vapor streams and that includes a sub-system for pre-cooling
the feed gas
stream and one or more mixed refrigerant streams using a second refrigerant.
BACKGROUND
100031 Natural gas, which is primarily methane, and other gases, are liquefied
under pressure
for storage and transport. The reduction in volume that results from
liquefaction permits
containers of more practical and economical design to be used. Liquefaction is
typically
accomplished by chilling the gas through indirect heat exchange by one or more
refrigeration
cycles. Such refrigeration cycles are costly both in terms equipment cost and
operation due
to the complexity of the required equipment and the required efficiency of
performance of the
refrigerant. There is a need, therefore, for gas cooling and liquefaction
systems having
improved refrigeration efficiency and reduced operating costs with reduced
complexity.
100041 Use of a mixed refrigerant in the refrigeration cycle(s) for a
liquefaction system
increases efficiency in that the warming curve of the refrigerant more closely
matches the
cooling curve of the gas. The refrigeration cycle for the liquefaction system
will typically
include a compression system for conditioning or processing the mixed
refrigerant. The
mixed refrigerant compression system typically includes one or more stages,
with each stage
including a compressor, a cooler and a separation and liquid accumulator
device. Vapor
exiting the compressor is cooled in the cooler, and the resulting two-phase or
mixed phase
stream is directed to the separation and liquid accumulator device, from which
vapor and
liquid exit for further processing and/or direction to the liquefaction heat
exchanger.
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100051 Separated liquid and vapor phases of the mixed refrigerant from the
compression
system may be directed to portions of the heat exchanger to provide more
efficient cooling.
Examples of such systems are provided in commonly owned U.S. Patent No.
9,441,877 to
Gushanas et al., U.S. Patent Application Publication No. US 2014/0260415 to
Ducote et al.
and U.S. Patent Application Publication No. US 2016/0298898 to Ducote et al.,
the contents
of each of which are hereby incorporated by reference.
[0006] Further increases in cooling efficiency and decreases in operating
costs in gas cooling
and liquefaction systems are desirable.
SUMMARY OF THE DISCLOSURE
[0007] There are several aspects of the present subject matter which may be
embodied
separately or together in the methods, devices and systems described and
claimed below.
These aspects may be employed alone or in combination with other aspects of
the subject
matter described herein, and the description of these aspects together is not
intended to
preclude the use of these aspects separately or the claiming of such aspects
separately or in
different combinations as set forth in the claims appended hereto.
[0008] In one aspect, a system for cooling a gas with a pre-cool refrigerant
and a mixed
refrigerant includes a pre-cool heat exchanger having a feed gas inlet adapted
to receive a
feed gas stream and a feed gas outlet, a pre-cool refrigerant inlet and a pre-
cool refrigerant
outlet and a liquefaction mixed refrigerant inlet and a liquefaction mixed
refrigerant outlet.
The pre-cool heat exchanger is configured to use the pre-cool refrigerant to
cool feed gas
passing through the pre-cool heat exchanger between the feed gas inlet and
outlet and to cool
liquefaction mixed refrigerant passing through the pre-cool heat exchanger
between the
liquefaction mixed refrigerant inlet and outlet. A pre-cool compressor system
includes a pre-
cool compressor having an inlet in fluid communication with the pre-cool
refrigerant outlet of
the pre-cool heat exchanger. The pre-cool compressor system also has a pre-
cool condenser
having an inlet in fluid communication with an outlet of the pre-cool
compressor. The pre-
cool condenser also has outlet in fluid communication with the pre-cool
refrigerant inlet of
the pre-cool heat exchanger. A liquefaction heat exchanger includes a
liquefying passage in
fluid communication with the feed gas outlet of the pre-cool heat exchanger, a
primary
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refrigeration passage, a high pressure vapor cooling passage and a cold
separator vapor
cooling passage, where the cold separator vapor cooling passage has an outlet
in fluid
communication with the primary refrigeration passage. A mixed refrigerant
compression
system includes a mixed refrigerant compressor having an inlet in fluid
communication with
an outlet of the primary refrigeration passage and a mixed refrigerant cooler
having an inlet
in fluid communication with an outlet of the mixed refrigerant compressor. The
mixed
refrigerant cooler also has an outlet in fluid communication with the
liquefaction mixed
refrigerant inlet of the pre-cool heat exchanger. The mixed refrigerant
compression system
also has a high pressure accumulator having an inlet in fluid communication
with the
liquefaction mixed refrigerant outlet of the pre-cool heat exchanger and a
vapor outlet in fluid
communication with an inlet of the high pressure vapor cooling passage of the
liquefaction
heat exchanger. A cold vapor separator has an inlet in fluid communication
with an outlet of
the high pressure vapor cooling passage of the liquefaction heat exchanger, a
vapor outlet in
fluid communication with an inlet of the cold separator vapor cooling passage
of the
liquefaction heat exchanger and a liquid outlet in communication with the
primary
refrigeration passage of the liquefaction heat exchanger.
100091 In another aspect, a method for cooling a feed gas stream includes the
steps of: pre-
cooling the feed gas stream in a pre-cool heat exchanger using a first
refrigerant to form a
pre-cooled feed gas stream and further cooling the pre-cooled feed gas stream
by i) cooling a
high pressure second refrigerant stream in the pre-cool heat exchanger to form
a cooled high
pressure second refrigerant stream, ii) separating the cooled high pressure
second refrigerant
stream to form a high pressure vapor stream and a high pressure liquid stream,
iii) cooling the
high pressure vapor stream in a liquefaction heat exchanger, to form a mixed
phase stream,
iv) separating the mixed phase stream with a cold vapor separator to form a
cold separator
vapor stream and a cold separator liquid stream, v) condensing the cold
separator vapor
stream in the liquefaction heat exchanger using the second refrigerant and
flashing, to form a
cold temperature refrigerant stream, vi) directing the cold temperature
refrigerant stream to
the liquefaction heat exchanger, vii) subcooling the high pressure liquid
stream to form a
subcooled high pressure liquid stream and combining with the cold temperature
refrigerant
stream in the liquefaction heat exchanger, viii) subcooling the cold separator
liquid stream to
form a subcooled cold separator liquid stream and combining with the cold
temperature
refrigerant stream in the liquefaction heat exchanger and ix) thermally
contacting the pre-
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cooled gas stream in the liquefaction heat exchanger with the cold temperature
refrigerant
stream
100101 In another aspect, a system for cooling a feed gas with a mixed
refrigerant includes a
pre-cool heat exchanger having a pre-cool refrigerant inlet configured to
receive a stream of
pre-cool refrigerant and a pre-cool refrigerant outlet and a liquefaction
mixed refrigerant inlet
and a liquefaction mixed refrigerant outlet. The pre-cool heat exchanger is
configured to use
the pre-cool refrigerant to cool liquefaction mixed refrigerant passing
through the pre-cool
heat exchanger between the liquefaction mixed refrigerant inlet and outlet. A
liquefaction
heat exchanger includes a liquefying passage configured to receive a stream of
the feed gas, a
primary refrigeration passage, a high pressure vapor cooling passage and a
cold separator
vapor cooling passage, where the cold separator vapor cooling passage has an
outlet in fluid
communication with the primary refrigeration passage. A mixed refrigerant
compression
system includes a mixed refrigerant compressor having an inlet in fluid
communication with
an outlet of the primary refrigeration passage. The mixed refrigerant
compression system
also includes a mixed refrigerant cooler having an inlet in fluid
communication with an outlet
of the mixed refrigerant compressor. The mixed refrigerant cooler has an
outlet in fluid
communication with the liquefaction mixed refrigerant inlet of the pre-cool
heat exchanger.
The mixed refrigerant compression system also includes a high pressure
accumulator having
an inlet in fluid communication with the liquefaction mixed refrigerant outlet
of the pre-cool
heat exchanger and a vapor outlet in fluid communication with an inlet of the
high pressure
vapor cooling passage of the liquefaction heat exchanger. A cold vapor
separator has an inlet
in fluid communication with an outlet of the high pressure vapor cooling
passage of the
liquefaction heat exchanger, a vapor outlet in fluid communication with an
inlet of the cold
separator vapor cooling passage of the liquefaction heat exchanger and a
liquid outlet in
communication with the primary refrigeration passage of the liquefaction heat
exchanger.
[00111 in another aspect, a method for cooling a feed gas stream includes the
steps of:
directing the feed gas stream into a liquefaction heat exchanger; cooling a
high pressure
mixed refrigerant stream in a pre-cool heat exchanger to form a cooled high
pressure mixed
refrigerant stream and cooling the feed gas stream in the liquefaction heat
exchanger by: i)
separating the cooled high pressure mixed refrigerant stream to form a high
pressure vapor
stream and a high pressure liquid stream, ii) cooling the high pressure vapor
stream in the
liquefaction heat exchanger to form a mixed phase stream, iii) separating the
mixed phase
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stream with a cold vapor separator to form a cold separator vapor stream and a
cold separator
liquid stream, iv) condensing the cold separator vapor stream in the
liquefaction heat
exchanger and flashing, to form a cold temperature refrigerant stream, v)
directing the cold
temperature refrigerant stream to the liquefaction heat exchanger, vi)
subcooling the high
pressure liquid stream in the liquefaction heat exchanger to form a subcooled
high pressure
liquid stream and combining with the cold temperature refrigerant stream in
the liquefaction
heat exchanger, vii) subcooling the cold separator liquid stream to form a
subcooled cold
separator liquid stream and combining with the cold temperature refrigerant
stream in the
liquefaction heat exchanger; and viii) thermally contacting the gas stream in
the liquefaction
heat exchanger with the cold temperature refrigerant stream.
BRIEF DESCRIPTION OF THE DRAWINGS
100121 Fig. 1 is a process flow and schematic illustrating a first embodiment
of the system
and method of the disclosure;
100131 Fig. 2 is a process flow and schematic illustrating a second embodiment
of the system
and method of the disclosure;
100141 Fig. 3 is a is a process flow and schematic illustrating a third
embodiment of the
system and method of the disclosure;
100151 Fig. 4 is a process flow and schematic illustrating a fourth embodiment
of the system
and method of the disclosure; and
100161 Fig. 5 is a process flow and schematic illustrating a fifth embodiment
of the system
and method of the disclosure.
DETAILED DESCRIPTION OF EMBODIMENTS
100171 Embodiments of the mixed refrigerant liquefaction system and method of
the
disclosure are illustrated in Figs. 1-5. It should be noted that while the
embodiments are
illustrated and described below in terms of liquefying natural gas to produce
liquid natural
gas, the invention may be used to liquefy or cool other types of gases.
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100181 Embodiments of the disclosure may use the mixed refrigerant
liquefaction system and
process described in commonly owned U.S. Patent No. 9,441,877 to Gushanas et
al.; U.S.
Patent Application Publication No. 2014/0260415, U.S. Patent Application No.
14/218,949,
to Ducote et al., and U.S. Patent App!. No. 62/561,417 to Ducote et al., the
contents of each
of which are hereby incorporated by reference.
100191 It should be noted herein that the passages and streams are sometimes
both referred to
by the same element number set out in the figures. Also, as used herein, and
as known in the
art, a heat exchanger is that device or an area in the device wherein indirect
heat exchange
occurs between two or more streams at different temperatures, or between a
stream and the
environment. As used herein, the terms "communication", "communicating", and
the like
generally refer to fluid communication unless otherwise specified.
Furthermore, although two
fluids in communication may exchange heat upon mixing, such an exchange would
not be
considered to be the same as heat exchange in a heat exchanger, although such
an exchange
can take place in a heat exchanger. As used herein, the term "reducing the
pressure of' (or
variations thereof) does not involve a phase change, while the term "flashing"
(or variations
thereof) involves a phase change, including even a partial phase change. As
used herein, the
terms, "high", "middle", "mid", "warm" and the like are relative to comparable
streams, as is
customary in the art.
100201 Generally, with reference to Fig. 1, a first embodiment the system of
the disclosure
includes a mixed refrigerant liquefaction system, indicated in general at 8,
including a multi-
stream liquefaction heat exchanger, indicated in general at 10, having a warm
end 12 and a
cold end 14. The heat exchanger receives a pre-cooled natural gas feed stream
16 that is
liquefied in cooling or liquefying passage 18 via removal of heat via heat
exchange with
refrigeration streams in the beat exchanger. As a result, a stream 20 of
liquid natural gas
(LNG) product is produced. The multi-stream design of the heat exchanger
allows for
convenient and energy-efficient integration of several streams into a single
exchanger.
Suitable heat exchangers include brazed aluminum heat exchangers, which may be
purchased
from Chart Energy & Chemicals, Inc. of The Woodlands, Texas. Such a plate and
fin, multi-
stream heat exchanger offers the further advantage of being physically
compact.
100211 The system of Fig. 1, including heat exchanger 10, may be configured to
perform
other gas processing options known in the prior art. These processing options
may require
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the gas stream to exit and reenter the heat exchanger one or more times and
may include, for
example, natural gas liquids recovery or nitrogen rejection.
100221 The removal of heat is accomplished in the heat exchanger using a mixed
refrigerant
that is processed and reconditioned using a liquefaction system mixed
refrigerant compressor
system indicated in general at 22. The mixed refrigerant compressor system
includes a first
stage suction drum 24, which receives a mixed refrigerant vapor stream 26 from
the primary
refrigeration passage 28 of the heat exchanger 10. The vapor stream is
compressed in a first
stage compressor 32 (which may be an individual compressor or a stage of a
single, multi-
stage compressor) and then cooled by first stage heat exchanger or cooler 34.
The resulting
mixed refrigerant vapor stream travels to a second stage suction drum 35 and
then to a second
stage compressor 36 (which may be an individual compressor or a stage of the
single, multi-
stage compressor) and, after compression, is cooled in second stage heat
exchanger or cooler
38.
100231 As is known in the art, the first and second stage suction drums 24 and
35, and the
remaining suction drums noted below, guard against liquid delivery to their
following
compressors, and are optional.
100241 In addition to the liquefaction heat exchanger 10, and associated
components
described below and in U.S. Patent Application No. 14/218,949, to Ducote et
al.,
incorporated by reference above, and mixed refrigerant compressor system 22,
the system of
Fig. 1 includes a pre-cooling system, indicated in general at 40. The pre-
cooling system
includes a pre-cool warm heat exchanger, indicated in general at 42a, and a
pre-cool cold heat
exchanger, indicated in general at 42b. Warm and cold heat exchangers 42a and
42b may be,
as an example only, CORE-1N-KETTLE heat exchangers, available from Chart
Energy &
Chemicals, Inc. of The Woodlands, Texas. Alternative types of heat exchangers
including,
but not limited to, shell and tube or thermosiphon type heat exchangers may be
used for
warm and cold heat exchangers 42a and 42b. The pre-cooling system may
alternatively
feature a single pre-cool heat exchanger or more than two pre-cool heat
exchangers.
100251 The pre-cooling system also includes a compressor system, indicated in
general at 44,
for processing and reconditioning a pre-cooling system refrigerant, such as
propane, butane,
ammonia or a chlorofluorocarbon. While the pre-cooling systems in the
embodiments
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described herein use propane, alternative refrigerants including, but not
limited to, butane,
ammonia or liquid fluorinated hydrocarbons may be used.
100261 The pre-cooling compressor system 44 includes a first stage suction
drum 46 that
receives a propane refrigerant vapor stream 48 from cold heat exchanger 42b,
as described in
greater detail below. Vapor stream 52 from the first stage suction drum
travels to a pre-
cooling compressor 54, and the resulting compressed stream travels to pre-
cooling condenser
56. A resulting propane refrigerant liquid stream travels to pre-cooling
refrigerant
accumulator 62. A propane refrigerant liquid stream 64 travels from the
accumulator to an
expansion device 66 so that a two-phase stream 72 enters a shell 74 of the
warm heat
exchanger 42a. A liquid level sensor 76 controls the setting of the expansion
device 66 so
that a proper liquid level is maintained within the shell 74.
10027] As in the case of all expansion devices referenced herein, expansion
device 66 may be
an expansion valve, such as a Joule-Thomson valve, or another type of
expansion device
including, but not limited to, a turbine or an orifice.
100281 The shell 74 of the pre-cool warm heat exchanger 42a houses a core 78
that receives a
natural gas feed stream 82. The core 78 of the warm feed gas heat exchanger,
and all such
cores discussed below, as an example only, may be a brazed aluminum heat
exchanger
(BAHX) or other heat exchanger type such as micro-channel or welded plate,
tubes or coils,
printed circuit heat exchanger, etc. The natural gas stream is cooled by the
propane liquid
refrigerant in the core 78, and the cooled natural gas stream exits the warm
heat exchanger
42a as stream 84. In an alternative embodiment, where the natural gas stream
82 is cooler
than the warm heat exchanger 42a, the gas stream may be routed directly to
cold heat
exchanger 42b as indicated by dashed line 84' in Fig. 1. In such an
embodiment, core 78
may be omitted.
100291 A warm propane refrigerant vapor stream 86 exits the shell 74 of the
pre-cool warm
heat exchanger 42a and travels to a second stage suction drum 88 and to an
inlet of pre-
cooling compressor 54.
100301 A propane refrigerant liquid stream exits the shell of the warm heat
exchanger as
stream 92 and travels to expansion device 94 so that a two-phase stream 96
enters a shell 98
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of the pre-cool cold heat exchanger 42b. A liquid level sensor 102 controls
the setting of the
expansion device 94 so that a proper liquid level is maintained within the
shell 98.
100311 The shell 98 of the cold heat exchanger 42b houses a core 104 that
receives the
natural gas feed stream 84 (or natural gas feed stream 84'). The natural gas
stream 84 is
further cooled (or cooled) by the propane liquid refrigerant in the core 104,
and the cooled
natural gas stream exits the cold heat exchanger 42b as pre-cooled stream 16
and travels to
liquefying passage 18 of the liquefaction heat exchanger 10. In an alternative
embodiment,
where the natural gas stream 82 is cooler than both the warm heat exchanger
42a and 42b, the
gas stream 84' of Fig. 1 may be routed directly to liquefying passage of the
liquefaction heat
exchanger. In such an embodiment, core 104 may also be omitted.
100321 The propane refrigerant vapor stream 48 exits the shell 98 of the pre-
cool cold heat
exchanger 42b and travels to the first stage suction drum 46.
100331 The high pressure mixed refrigerant stream 112 from the second stage
compressor 36
and heat exchanger 38 of the mixed refrigerant compression system travels to a
core 114
positioned within the shell 74 of the pre-cool warm heat exchanger 42a. The
mixed
refrigerant flowing through core 114 is cooled by the liquid propane
refrigerant within shell
74, and the resulting cooled mixed refrigerant stream 116 is directed to the
cold mixed
refrigerant core 118 positioned within the shell 98 of the pre-cool cold heat
exchanger 42b.
The mixed refrigerant flowing through core 118 is cooled by the liquid propane
refrigerant
within shell 98, and a resulting mixed refrigerant (MR) mixed phase stream 122
is directed to
a high pressure accumulator 124. While an accumulator drum is illustrated as
high pressure
accumulator 124, alternative separation devices may be used, including, but
not limited to,
another type of vessel, a cyclonic separator, a distillation unit, a
coalescing separator or mesh
or vane type mist eliminator. The same applies for the remaining separation
devices or drums
discussed herein.
100341 High pressure vapor refrigerant stream 126 exits the vapor outlet of
the accumulator
124 and travels to the warm end of the heat exchanger 10.
100351 High pressure liquid refrigerant stream 128 exits the liquid outlet of
accumulator 124
and also travels to the warm end of the heat exchanger. After cooling in the
heat exchanger
10, via high pressure liquid cooling passage 125, it is flashed at 129 and
travels to warm
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temperature separator 131. Vapor stream 127 and liquid stream 133 travel from
the warm
temperature separator 131 to the primary refrigeration passage 28 of the heat
exchanger 10.
100361 The heat exchanger 10 also receives and cools, via high pressure vapor
cooling
passage 135, the high pressure vapor stream 126 from the high pressure
accumulator 124 and
cools it so that it is partially condensed. The resulting mixed phase cold
separator feed
stream 132 is provided to a cold vapor separator 134 so that cold separator
vapor stream 136
and cold separator liquid stream 138 are produced.
100371 The cold separator vapor stream 136 is cooled and condensed in the heat
exchanger
10, via cold separator vapor cooling passage 141, into liquid stream 142,
flashed through
expansion device 144 and directed to cold temperature separator 146 to form a
cold
temperature liquid stream 152 and a cold temperature vapor stream 154, which
are directed to
the primary refrigeration passage 28 of the heat exchanger 10 as a cold
temperature
refrigerant stream.
100381 The cold separator liquid stream 138 is cooled in the heat exchanger
10, via cold
separator liquid cooling passage 143, to form subcooled cold separator liquid
160, which is
flashed at 162 and directed to mid temperature separator 164. A resulting
liquid stream 166
and a resulting vapor stream 168 are directed to the primary refrigeration
passage 28 of the
heat exchanger 10.
100391 The combined refrigerant streams from the warm temperature separator
131, the mid
temperature separator 164 and the cold temperature separator 146 provide the
refrigeration
for liquefying pre-cooled feed gas stream 16 within the liquefying or cooling
passage 18 of
the heat exchanger 10, and exit the primary refrigeration passage 28 of the
liquefaction heat
exchanger as a combined return refrigerant stream 26, which preferably is in
the vapor phase.
The return refrigerant stream 26 flows to the suction drum 24, which results
in vapor mixed
refrigerant stream 27, as referenced previously.
100401 The liquefied natural gas stream 172 exits the cold side of the heat
exchanger and may
be optionally expanded, using expansion device 174, and delivered to storage
or a process.
100411 The embodiment of Fig. 1 therefore shows a propane (C3) pre-cooled
mixed
refrigerant (MR) process in combination with a cold vapor separator (CVS)
located in the
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main liquefaction section of the process. The combination of C3 pre-cooling
and MR with a
CVS results in a more efficient process than pre-cooling without the CVS and
with lower
equipment cost and also facilitates higher plant capacities. The combination
of pre-cooling
and CVS allows the C3 system to operate at a significantly warmer temperature
such as, as an
example only, approximately -5 C vs. -35 to -40 C, with high efficiency, which
reduces the
propane system cost and power consumption.
100421 The process of Fig. 1 can be used with any MR liquefaction process that
utilizes a
CVS.
100431 It should be noted that while Fig. 1 shows two stages of pre-cooling in
the pre-cooling
system 40, one or more stages of pre-cooling may alternatively be used.
100441 Furthermore, while Fig. 1 shows an MR liquefaction system 8 featuring
separate
warm, mid and cold temperature separators, any of these may be combined or, in
certain
cases, the separators may be eliminated. Furthermore, while these separators
are illustrated
as stand pipes, alternative types of separators known in the art may be used.
[0045] With the exceptions discussed below, the embodiments of Figs. 2-4
feature the same
mixed refrigerant compressor system, mixed refrigerant liquefaction system and
pre-cooling
compressor system components and operation as described above with reference
to Fig. 1,
and thus common reference numbers are used to indicate these portions, and
common
components, of the systems.
100461 A second embodiment of the system of the disclosure is presented in
Fig. 2. In this
embodiment, two high pressure MR accumulators are used, instead of the single
high
pressure MR accumulator 124 of Fig. 1. More specifically, stream 182 exiting
the second
stage compression and cooling cycle of the MR compressor system 22 is directed
to the core
114 of the warm pre-cool heat exchanger 42a. The core 114 cools the stream 182
using the
liquid propane refrigerant within shell 74. The resulting cooled MR stream 186
travels to a
first high pressure MR accumulator 188. The resulting vapor MR stream 192
travels to a
core 194 positioned within the pre-cool cold heat exchanger 42b where it is
cooled by the
liquid propane refrigerant within shell 98. The resulting cooled stream 198
travels to a
second high pressure MR accumulator 202.
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[0047] The vapor stream 204 leaving the second high pressure MR accumulator
202 is
cooled within the liquefaction heat exchanger 10, via passage 206, and is
directed to cold
vapor separator 208. The vapor stream exiting the cold vapor separator is
processed as
described above with regard to Fig. 1.
[0048] The liquid stream 212 leaving the second high pressure MR accumulator
202 is
cooled within the liquefaction heat exchanger 10, via passage 214, is flashed
via expansion
device 216 and is directed to mid temperature separator 164, where it is
combined with the
cooled and flashed liquid stream from the cold vapor separator 208. The vapor
and liquid
streams exiting the mid temperature separator are directed to the primary
refrigeration
passage 28.
100491 The liquid MR stream exiting the first high pressure MR accumulator 188
travels to a
core 196 positioned within the pre-cool cold heat exchanger 42b where it is
cooled by the
liquid propane refrigerant within shell 98. The resulting cooled stream 218 is
cooled in the
liquefaction heat exchanger 10 via passage 220, and the resulting cooled
liquid stream is
flashed via expansion device 222 and delivered to warm temperature separator
131. The
vapor and liquid streams exiting the warm temperature separator are directed
to the primary
refrigeration passage 28.
[0050] In addition, in the embodiment of Fig. 2, the pre-cooling system is
used to cool the
discharge stream 224 exiting the first stage compression and cooling cycle of
the MR
compressor system 22. More specifically, the pre-cool warm heat exchanger 42a
contains a
core 226 which receives the stream 224 through an inteistage mixed refrigerant
inlet and
cools it using the propane liquid refrigerant within the shell 74. The
resulting cooled stream
exits the core through an interstage mixed refrigerant outlet and travels to
an Interstage or
MR low pressure accumulator 228. The resulting vapor stream 232 is directed to
an input of
the second stage compressor 36 of the MR compressor system 22. The liquid
stream 234
exiting the MR low pressure accumulator 228 is received by a core 236
positioned within the
shell 98 of the cold heat exchanger 42b. The resulting cooled stream 238 is
cooled in passage
242 of the liquefaction heat exchanger 10, flashed via expansion device 244
and directed to
the primary refrigeration passage 28 of the heat exchanger 10.
[0051] It is to be understood, with regard to the embodiment of Fig. 2, that
pre-cooling the
discharge stream (224) of the first compression and cooling stage of the MR
compressor
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system 22 before compressing in the second stage and incorporating first and
second MR
high pressure accumulators (188 and 202) in the process are distinct and
independent and
may be utilized in combination or separately.
[0052] Furthermore, the pre-cooled liquid stream 224 from the first
compression and cooling
stage may be introduced into the MR liquefaction system 8 separately, as shown
in Fig. 2, or
combined with any of the other refrigeration streams in the separators of the
MR liquefaction
system 8 or in some cases without any separators.
[0053] A third embodiment of the system of the disclosure is presented in Fig.
3. In this
embodiment, a warm mixed refrigerant (MR) pre-cooling system, indicated in
general at 252
is used in place of the propane pre-cooling system of Figs. 1 and 2.
[0054] The MR pre-cooling system includes a warm MR pre-cooling heat
exchanger,
indicated in general at 254, that includes a pre-cooling passage 256 that
receives natural gas
feed stream 82.
[0055] The MR pre-cooling system also includes a pre-cooling compressor system
262 that
includes a first stage suction drum 264 that receives a pre-cooling MR vapor
stream 266 from
a pre-cooling primary refrigeration passage 268 of the heat exchanger 254.
Vapor stream 272
from the first stage suction drum travels to an inlet of pre-cooling
compressor 272, and the
resulting compressed stream travels to pre-cooling condenser 274. A resulting
MR liquid
stream travels to pre-cooling MR accumulator 276. The vapor stream from the
accumulator
276 may either be vented via valve 278 or directed via a second valve to a
second stage
suction drum 284. The vapor stream 286 from the second stage suction drum 284
travels to
an inlet of pre-cooling compressor 272.
[0056] A liquid pre-cooling MR stream 292 travels from accumulator 276 through
cooling
passage 294 of the heat exchanger 254, and the resulting cooled liquid stream
travels to an
expansion device 296 and is flashed, with the resulting mixed phase stream
entering pre-
cooling cold separator 302. A portion of (or all of) the cooled liquid stream
leaving passage
294 of the heat exchanger may be directed to a secondary pre-cooling
refrigeration passage
304 of the heat exchanger using valve 298 depending on the system temperature
and duty
needs. The vapor stream 306 exiting the secondary pre-cooling refrigeration
passage 304 is
directed to second stage suction drum 284. Both the vapor and liquid pre-
cooling MR
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streams (308 and 312, respectively) from the pre-cooling cold separator 302
are directed to
the pre-cooling primary refrigeration passage 268 of the heat exchanger 254.
100571 The natural gas feed stream flowing through pre-cooling passage 256 of
the pre-
cooling heat exchanger 254 is pre-cooled via refrigeration passages 268 and
304 of the heat
exchanger, and the resulting cooled natural gas stream 314 is directed to the
liquefaction heat
exchanger 10 to be liquefied.
100581 The liquefaction compressor system 316, similar to the embodiments of
Figs. 1 and 2,
features a first stage compression and cooling cycle, that produces first
stage liquefaction MR
stream 318, and a second stage compression and cooling cycle, that produces
second stage
liquefaction MR stream 322. Liquefaction MR streams 318 and 322 are further
cooled in the
pre-cooling heat exchanger 254 via passages 324 and 326, and the resulting
mixed phase
stream 328 exiting passage 324 travels to a liquefaction MR low pressure
accumulator 332,
while the resulting mixed phase stream 334 travels to liquefaction MR high
pressure
accumulator 336.
100591 Liquefaction MR vapor stream 338 travels from the liquefaction MR low
pressure
accumulator 332 to second stage suction drum 342 of the liquefaction
compressor system
316, with the resulting vapor stream being directed to the second stage
compression and
cooling cycle. Liquefaction MR liquid stream 344 from the liquefaction MR low
pressure
accumulator 332 is cooled in passage 346 of the liquefaction heat exchanger
350, flashed via
expansion device 348 and directed to the primary refrigeration passage 352 of
the heat
exchanger 350.
100601 The liquefaction MR vapor stream 354 leaving the liquefaction MR high
pressure
accumulator 336 is cooled within the liquefaction heat exchanger 350, via
passage 356, and is
directed to cold vapor separator 358. The vapor stream exiting the cold vapor
separator may
be processed as described above with regard to Fig. 1.
100611 The liquid stream 362 leaving the liquefaction MR high pressure
accumulator 336 is
cooled within the liquefaction heat exchanger 350, via passage 364, is flashed
via expansion
device 366 and is directed to mid temperature separator 368, after it is
combined with the
cooled and flashed liquid stream from the cold vapor separator 358 (which is
functionally
equivalent to combining the streams in the mid temperature separator, as
indicated in Fig. 2).
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The vapor and liquid streams exiting the mid temperature separator are
directed to the
primary refrigeration passage 352 of the heat exchanger 350.
100621 It should be noted that, with regard to the embodiment of Fig. 3, pre-
cooling the
liquefaction MR compression system 316 first stage discharge (318) before
compressing in
the second stage is an optional feature and may be utilized in combination
with the other
features or not used at all. In addition, the mixed refrigerants used in the
pre-cooling system
and the liquefaction system may be of the same or different compositions.
100631 In addition, it should be noted that the MR pre-cooling system
illustrated at 262 in
Fig. 3 is merely an example of a suitable MR system ¨ other MR systems, and
non-mixed
refrigerant systems, known in the art may be used instead as the pre-cooling
system.
100641 The embodiment of the system illustrated in Fig. 4 is essentially the
same as the
embodiment of Fig. 1, including the propane pre-cooling system, indicated in
general at 370,
with the exception of the configuration of the pre-cooling heat exchangers.
More
specifically, in the embodiment of the system illustrated in Fig. 4, the pre-
cooling system 370
includes a pre-cool warm heat exchanger, indicated in general at 372a, and a
pre-cool cold
heat exchanger, indicated in general at 372b. Warm and cold heat exchangers
372a and 372b
may be, as an example only, CORE-IN-KETTLE heat exchangers, available from
Chart
Energy & Chemicals, Inc. of The Woodlands, Texas. Alternative types of heat
exchangers
including, but not limited to, shell and tube or thermosiphon type heat
exchangers may be
used.
100651 In the embodiment of Fig. 4, a core 374 (which, as an example only, may
be a brazed
aluminum heat exchanger (BAHX) or other heat exchanger type such as micro-
channel or
welded plate, etc.) extends thru the internal head 376 between the shells 378
and 382 of the
warm and cold heat exchangers 372a and 372b such that the process stream,
which is the
discharge stream 384 from the second compression and cooling stage of the
liquefaction MR
compressor system 386, is continuous thru the core 374. The benefit of this
arrangement is
that the cooled and partially condensed process stream is not subject to two-
phase flow ma!-
distribution, which adversely effects system performance, as could be
encountered if the heat
exchanger design was multiple cores piped in series, as shown in Fig. 1. The
arrangement of
Fig. 4. reduces the power consumption of the process, either the propane
system or the
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liquefaction system or both, attributed to mal-distribution or simplifies the
equipment count
and reduces cost to eliminate mai-distribution effects.
[0066] It should be noted that the warm and cold heat exchangers 372a and 372b
can utilize
an internal head 376 of any shape, including flat plate. Furthermore, while
Fig. 4 shows a
propane (C3) pre-cooled MR process, the embodiment of Fig. 4 can be used with
any process
that utilizes at least two boiling refrigerant cooling steps. In addition,
while propane (C3) is
described as the coolant for the pre-cooling system of Fig. 4, any refrigerant
may be used,
such as, but not limited to, butane, ammonia or liquid fluorinated
hydrocarbons, etc.
Furthermore, while the system of Fig. 4 shows two stages of pre-cooling, two
or more stages
of cooling may be used. In addition, while Fig. 4 shows a separate feed
exchanger, the feed
exchanger may be combined with MR exchanger.
100671 In the embodiment illustrated in Fig. 5, a chilled water cooling
system, indicated in
general at 402, is used to pre-cool the discharge stream 404 from the second
compression and
cooling stage of the liquefaction MR compressor system 406. More specifically,
water is
pumped via pump 412 to a coolant heat exchanger 414. The heat exchanger also
receives the
MR discharge stream 404 and cools it. The chilled water is water or
water/glycol mixture
cooled in a pre-cool refrigerant system that may be, but not limited to, a
mechanical chiller or
adsorption chiller or thermoelectric chiller or thermoacoustic refrigerator
and is always colder
than the temperature that can be achieved by either air cooling or water
evaporative cooling.
[0068] The cooled MR stream 416 then flows to high pressure accumulator 124,
with the
resulting liquid and vapor streams directed to the liquefaction heat exchanger
420 of the MR
liquefaction system 408, as in previous embodiments.
[0069] While a single chiller heat exchanger 414 is illustrated in Fig. 5,
multiple chiller heat
exchangers, in parallel or in series, may be used instead.
[0070] As in previous embodiments, the liquefaction MR compressor system
provides
refrigerant to an MR liquefaction system 408 that includes a cold vapor
separator (CVS) 410.
The combination of pre-cooling with a chilled water cooling system and MR with
CVS
results in a more efficient process than pre-cooling without the CVS and with
lower
equipment cost and also facilitates higher plant capacities. The combination
of pre-cooling
and CVS allows the chilled water cooling system to operate at a significantly
warmer
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temperature, approximately -5 C vs. -35 to -40 C. It also allows the chiller
equipment to be
located away from the hydrocarbon containing equipment, which reduces the
system cost and
provides plot plan flexibility. The process can be used with any MR
liquefaction process that
utilizes a CVS.
[0071] While Fig. 5 shows a chilled water pre-cooled MR process, any chilled
cooling fluid
may be used, such as, but not limited to, ammonia, water, water glycol mix,
lithium bromide
solution, liquid fluorinated hydrocarbons, liquid hydrocarbons, etc. In
addition, while Fig. 5
shows a shell and tube heat exchanger for the pre-cooling system heat
exchanger 414, any
heat exchanger type may be used. Furthermore, while Fig. 5 shows separate
warm, mid and
cold temperature stand pipes 422, 424 and 426, any of these may be combined or
in certain
cases, the stand pipe may be eliminated. Although not explicitly shown, the
chilled water
cooling system may also be used to cool the feed gas and/or cool the 1st stage
discharge as
shown in Fig. 2 or provide cooling for turbine inlet air for the gas turbine
driver or cool
multiple liquefaction systems.
100721 There are several aspects of the present subject matter which may be
embodied
separately or together in the methods, devices and systems described and
claimed below.
These aspects may be employed alone or in combination with other aspects of
the subject
matter described herein, and the description of these aspects together is not
intended to
preclude the use of these aspects separately or the claiming of such aspects
separately or in
different combinations as set forth in the claims appended hereto.
[0073] While the preferred embodiments of the invention have been shown and
described, it
will be apparent to those skilled in the art that changes and modifications
may be made
therein without deputing from the spirit of the invention, the scope of which
is defined by the
appended claims.
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