U.S. patent application number 12/333500 was filed with the patent office on 2010-06-17 for alternative pre-cooling arrangement.
This patent application is currently assigned to Air Products and Chemicals, Inc.. Invention is credited to Christopher Michael Ott, Mark Julian Roberts.
Application Number | 20100147024 12/333500 |
Document ID | / |
Family ID | 42062483 |
Filed Date | 2010-06-17 |
United States Patent
Application |
20100147024 |
Kind Code |
A1 |
Roberts; Mark Julian ; et
al. |
June 17, 2010 |
ALTERNATIVE PRE-COOLING ARRANGEMENT
Abstract
A natural gas liquefaction system, the system comprising a first
precooling refrigeration system that accepts at least a natural gas
feed stream, a second precooling refrigeration system that accepts
at least a first refrigerant stream; and a cryogenic heat exchanger
fluidly connected to the first precooling refrigeration system and
the second precooling refrigeration system that accepts the natural
gas feed stream from the first precooling refrigeration system and
the first refrigerant stream from the second precooling
refrigeration system to liquefy the natural gas feed stream, where
the second precooling refrigeration system accepts only stream(s)
having a composition different from the stream(s) accepted by the
first precooling refrigeration system.
Inventors: |
Roberts; Mark Julian;
(Kempton, PA) ; Ott; Christopher Michael;
(Allentown, PA) |
Correspondence
Address: |
AIR PRODUCTS AND CHEMICALS, INC.;PATENT DEPARTMENT
7201 HAMILTON BOULEVARD
ALLENTOWN
PA
181951501
US
|
Assignee: |
Air Products and Chemicals,
Inc.
Allentown
PA
|
Family ID: |
42062483 |
Appl. No.: |
12/333500 |
Filed: |
December 12, 2008 |
Current U.S.
Class: |
62/612 |
Current CPC
Class: |
F25J 1/0022 20130101;
F25J 1/0268 20130101; F25J 1/0085 20130101; F25J 1/0052 20130101;
F25J 1/0218 20130101; F25J 1/0287 20130101; F25J 1/0283 20130101;
F25J 1/0295 20130101; F25J 1/0055 20130101; F25J 1/0095 20130101;
F25J 1/0097 20130101; F25J 1/0292 20130101; F25J 1/0216 20130101;
F25J 1/029 20130101; F25J 1/0082 20130101; F25J 1/0087
20130101 |
Class at
Publication: |
62/612 |
International
Class: |
F25J 1/00 20060101
F25J001/00 |
Claims
1. A natural gas liquefaction system, the system comprising: a
first precooling refrigeration system that accepts at least a
natural gas feed stream; a second precooling refrigeration system
that accepts at least a first refrigerant stream; and a cryogenic
heat exchanger fluidly connected to the first precooling
refrigeration system and the second precooling refrigeration system
that accepts the natural gas feed stream from the first precooling
refrigeration system and the first refrigerant stream from the
second precooling refrigeration system to liquefy the natural gas
feed stream, wherein the second precooling refrigeration system
accepts only stream(s) having a composition different from the
stream(s) accepted by the first precooling refrigeration
system.
2. The system of claim 1, wherein the first refrigerant stream is a
mixed refrigerant stream.
3. The system of claim 1, wherein the first refrigerant stream
comprises nitrogen, methane, ethane, and propane.
4. The system of claim 1, further comprising a subcooler exchanger
fluidly connected to the cryogenic heat exchanger, wherein the
subcooler exchanger accepts a second refrigerant stream from the
cryogenic heat exchanger to subcool the natural gas feed stream
through indirect heat exchange.
5. The system of claim 1, wherein the first precooling
refrigeration system and the second precooling refrigeration system
each comprise: at least one propane evaporator; and a propane
compressor fluidly coupled to the at least one propane evaporator
and adapted to accept at least one propane vapor stream.
6. The system of claim 1, wherein the first precooling
refrigeration system and the second precooling refrigeration system
are CO.sub.2 refrigeration systems.
7. The system of claim 1, wherein the first precooling
refrigeration system comprises at least one heat exchanger that
accepts at least two load streams.
8. The system of claim 5, further comprising a first driver and a
second driver, wherein the first driver drives the propane
compressor of the first precooling refrigeration system, the
propane compressor of the second precooling refrigeration system;
and a first high pressure refrigerant compressor, and wherein the
second driver drives a first medium pressure refrigerant compressor
and a first low pressure refrigerant compressor.
9. The system of claim 5, further comprising a first driver and a
second driver, wherein the first driver drives the propane
compressor of the first precooling refrigeration system and a first
low pressure refrigerant compressor, and wherein the second driver
drives the propane compressor of the second precooling
refrigeration system and a first high pressure refrigerant
compressor.
10. The system of claim 5, further comprising a first driver and a
second driver, wherein the first driver drives the propane
compressor of the first precooling refrigeration system and the
propane compressor of the second precooling refrigeration system
and the second driver drives a first low pressure refrigerant
compressor and a first high pressure refrigerant compressor.
11. The system of claim 10, further comprising a third driver,
wherein the third driver drives a second low pressure refrigerant
compressor and a second high pressure refrigerant compressor.
12. The system of claim 8, wherein the first driver and the second
driver are gas turbines.
13. The system of claim 1, wherein the cryogenic heat exchanger is
a wound-coil heat exchanger.
14. A method for liquefying natural gas, the method comprising the
steps of: providing a natural gas feed stream; providing a first
refrigerant stream; precooling in a first precooling refrigeration
system at least the natural gas feed stream; precooling in a second
precooling refrigeration system at least the first refrigerant
stream; and vaporizing the precooled first refrigerant stream in a
cryogenic heat exchanger to cool the precooled natural gas feed
stream through indirect heat exchange, wherein the second
precooling refrigeration system precools only stream(s) having a
composition different from the stream(s) precooled by the first
precooling refrigeration system.
15. The method of claim 14, wherein the natural gas feed stream and
the first refrigerant stream are precooled to +60.degree. F. to
-100.degree. F.
16. The method of claim 14, further comprising providing a second
refrigerant stream, wherein the second refrigerant stream is
precooled in the first precooling refrigeration system or the
second precooling refrigeration system and is vaporized to subcool
the natural gas feed stream.
17. The method of claim 14, wherein the first refrigerant stream is
a mixed refrigerant stream.
18. A natural gas liquefaction system for large capacity
liquefaction plants, the system comprising: a first precooling
refrigeration system that accepts one stream selected from the
group consisting of: a natural gas feed stream, and an at least one
refrigerant stream; a second precooling refrigeration system that
accepts any remaining stream(s) not accepted by the first
precooling refrigeration system and from the group consisting of:
the natural gas feed stream, and the at least one refrigerant
stream; and a cryogenic heat exchanger fluidly connected to the
first precooling refrigeration system and the second precooling
refrigeration system and adapted to accept the natural gas feed
stream and the at least one refrigerant stream from the first
precooling refrigeration system and the second precooling
refrigeration system, wherein the at least one refrigerant stream
is used to liquefy the natural gas feed stream, wherein the second
precooling refrigeration system accepts only stream(s) having a
composition different from the stream(s) accepted by the first
precooling refrigeration system.
19. The system of claim 18, wherein the at least one refrigerant
stream is a mixed refrigerant stream.
20. The system of claim 18, wherein the at least one refrigerant
stream comprises a first refrigerant stream and a second
refrigerant stream.
Description
BACKGROUND
[0001] The present invention relates to a system and method for
liquefaction of a gas stream, and more specifically, to a system
and method for liquefaction of a natural gas stream in large
capacity liquefaction plants.
[0002] Over the past few years, the liquid natural gas (LNG)
industry has moved towards using large capacity liquefaction plants
to achieve favorable economics associated with the large plants.
Scale-up problems arise, however, when refrigerant mass and volume
flow rates are increased. For example, the design of compression
equipment, particularly the compression equipment associated with
precooling, becomes problematic because the increased flow rates
require larger compressor impellers with higher tip speeds, thicker
and heavier casings, and higher inlet velocities to the impellers.
As the equipment is scaled up, the design of the compressor becomes
more problematic as fundamental aerodynamic limits are approached
and, thus, the scale up may be limited by these considerations. In
addition these precooling compressors are large and often contain
multiple stages. Moreover, scale-up in many instances requires
large, heavy equipment that can be difficult and costly to
manufacture and/or install.
[0003] U.S. Pat. No. 6,962,060 (Petrowski et al.) assigned to the
assignee of the present invention, discloses one alternative system
designed for liquefaction at large plants that includes a
compressor system comprising a first compressor having a first
stage and a second stage wherein the first stage of the first
compressor is adapted to compress a first gas and the second stage
of the first compressor is adapted to compress a combination of a
fourth gas and an intermediate compressed gas from the first stage
of the first compressor; and a second compressor having a first
stage and a second stage wherein the first stage of the second
compressor is adapted to compress a second gas and the second stage
of the second compressor is adapted to compress a combination of a
third gas and an intermediate compressed gas from the first stage
of the second compressor.
[0004] There is a need for a method and system that provides stable
operation at full rates and during turndown for larger capacity
liquefaction plants.
BRIEF SUMMARY
[0005] Embodiments of the present invention satisfy this need in
the art by providing a liquid natural gas liquefaction system and
process that is stable and operational at full rates and during
turndown for larger capacity liquefaction plants.
[0006] In one exemplary embodiment a natural gas liquefaction
system is disclosed, the system comprises: a first precooling
refrigeration system that accepts at least a natural gas feed
stream; a second precooling refrigeration system that accepts at
least a first refrigerant stream; and a cryogenic heat exchanger
fluidly connected to the first precooling refrigeration system and
the second precooling refrigeration system that accepts the natural
gas feed stream from the first precooling refrigeration system and
the first refrigerant stream from the second precooling
refrigeration system to liquefy the natural gas feed stream,
wherein the second precooling refrigeration system accepts only
stream(s) having a composition different from the stream(s)
accepted by the first precooling refrigeration system.
[0007] In another exemplary embodiment, a method for liquefying
natural gas is disclosed, the method comprising the steps of:
providing a natural gas feed stream; providing a first refrigerant
stream; precooling in a first precooling refrigeration system at
least the natural gas feed stream; precooling in a second
precooling refrigeration system at least the first refrigerant
stream; and vaporizing the precooled first refrigerant stream in a
cryogenic heat exchanger to cool the precooled natural gas feed
stream through indirect heat exchange, wherein the second
precooling refrigeration system precools only stream(s) having a
composition different from the stream(s) precooled by the first
precooling refrigeration system.
[0008] In yet another exemplary embodiment, a natural gas
liquefaction system for large capacity liquefaction plants is
disclosed, the system comprising: a first precooling refrigeration
system that accepts one stream selected from the group consisting
of:
[0009] a natural gas feed stream, and an at least one refrigerant
stream; a second precooling refrigeration system that accepts any
remaining stream(s) not accepted by the first precooling
refrigeration system and from the group consisting of: the natural
gas feed stream, and the at least one refrigerant stream; and a
cryogenic heat exchanger fluidly connected to the first precooling
refrigeration system and the second precooling refrigeration system
and adapted to accept the natural gas feed stream and the at least
one refrigerant stream from the first precooling refrigeration
system and the second precooling refrigeration system, wherein the
at least one refrigerant stream is used to liquefy the natural gas
feed stream, wherein the second precooling refrigeration system
accepts only stream(s) having a composition different from the
stream(s) accepted by the first precooling refrigeration
system.
BRIEF DESCRIPTION OF THE EXEMPLARY DRAWINGS
[0010] The foregoing brief summary, as well as the following
detailed description of exemplary embodiments, is better understood
when read in conjunction with the appended drawings. For the
purpose of illustrating embodiments of the invention, there is
shown in the drawings exemplary embodiments of the invention;
however, the invention is not limited to the specific methods and
instrumentalities disclosed. In the drawings:
[0011] FIG. 1 is a flow chart illustrating an exemplary system and
method involving aspects of the present invention;
[0012] FIG. 2A is a flow chart illustrating an exemplary system and
method involving aspects of the present invention;
[0013] FIG. 2B is a flow chart illustrating an exemplary system and
method involving aspects of the present invention;
[0014] FIG. 3 is a flow chart illustrating an exemplary system and
method involving aspects of the present invention;
[0015] FIG. 4 is a flow chart illustrating an exemplary system and
method involving aspects of the present invention;
[0016] FIG. 5 is a flow chart illustrating an exemplary system and
method involving aspects of the present invention;
[0017] FIG. 6 is a flow chart illustrating an exemplary system and
method involving aspects of the present invention;
[0018] FIG. 7A is a flow chart illustrating an exemplary system and
method involving aspects of the present invention;
[0019] FIG. 7B is a flow chart illustrating an exemplary system and
method involving aspects of the present invention;
[0020] FIG. 8A is a flow chart illustrating an exemplary system and
method involving aspects of the present invention; and
[0021] FIG. 8B is a flow chart illustrating an exemplary system and
method involving aspects of the present invention.
DETAILED DESCRIPTION
[0022] FIG. 1 illustrates an exemplary embodiment of the invention
as applied to a pre-cooled refrigerant system and process. In this
exemplary system 100, propane is used to precool both a natural gas
feed stream 102 and a liquefaction refrigerant stream 104. The
natural gas feed stream 102 may be pretreated, for example. The
liquefaction refrigerant stream 104 may be a pure or a mixed
refrigerant, for example. It should be noted that while the
exemplary embodiments described below may refer to the liquefaction
refrigerant stream as a mixed refrigerant stream, the liquefaction
refrigerant stream described below may also be a pure refrigerant
stream, for example. Depending on refrigerant availability in the
local area and system requirements (e.g., adjusting the composition
of the mixed refrigerant to match the cooling curve for optimal
cooling performance), the liquefaction refrigerant stream 104 may
comprise one or more of the following: nitrogen, methane, ethylene,
ethane, propylene, propane, iso-butane, n-butane, and iso-pentane,
for example.
[0023] The compression of the vapor resulting from the cooling of
the natural gas feed stream 102 may occur in one compressor 118
while the compression of the propane vapor generated from cooling
of liquefaction refrigerant stream 104 may occur in a separate
compressor 126.
[0024] Precooling of the natural gas feed stream 102 and the mixed
refrigerant stream 104 may be accomplished by vaporizing a
precooling refrigerant such as propane at four different pressure
levels in closed-loop precooling refrigeration system(s). The
natural gas feed stream 102 may be precooled because of equipment
limitations and for efficiency purposes. It should be noted that
while propane may be used as the precooling refrigerant for
vaporizing at four different pressure levels (as illustrated in
exemplary FIGS. 1-7A), carbon dioxide, methane, propane, butane,
iso-butane, propylene, ethane, ethylene, R22, HFC refrigerants,
including, but not limited to, R410A, R134A, R507, R23, or
combinations thereof, may also be used, for example.
[0025] Cooling of the natural gas feed stream 102 is performed in
unit 106. Unit 106 may comprise a series of heat exchangers,
valves, and separators as illustrated in FIG. 2A. Natural gas feed
stream 102 is cooled by indirect heat exchange against a precooling
refrigerant in a series of propane evaporators 202, 204, 206, 208
that may operate at successively lower pressures (202 being the
highest and 208 being the lowest, for example) producing cooled
successive streams 203, 205, 207, and 150. The evaporation of
propane at the four pressures results in four propane vapor streams
110, 112, 114, 116 that are then compressed in compressor 118. The
resulting compressed stream 120 is then condensed in propane
condenser 122, producing liquid stream 124 for reintroduction into
the series of propane evaporators 202, 204, 206, 208. Propane
condensers used in these types of methods and systems may include,
for example, a propane de-superheater, a condenser, an accumulator,
and a propane subcooler. It should be noted that while this
exemplary embodiment illustrated in FIGS. 1, 2A, 2B, 3, 4, 5, 6,
and 7A uses a four stage pre-cooling system, the pre-cooling system
may comprise a single-stage, a two-stage, a three-stage, or systems
with greater than four stages, for example, where the series of
propane evaporators may operate at successively lower
pressures.
[0026] Cooling of the mixed refrigerant stream 104 is performed in
unit 108. Unit 108 may also comprise a series of heat exchangers,
valves, and separators as illustrated in FIG. 2B. The mixed
refrigerant stream 104 may also be cooled by indirect heat exchange
against the precooling refrigerant in a series of propane
evaporators 222, 224, 226, 228 that may operate at successively
lower pressures (222 being the highest and 228 being the lowest,
for example) producing cooled successive streams 223, 225, 227, and
138. The evaporation of propane at the four pressures results in
four propane vapor streams 130, 132, 134,136 that are then
compressed in compressor 126. The resulting compressed stream 127
is then condensed in propane condenser 128, producing liquid stream
129 for reintroduction into the series of propane evaporators 222,
224, 226, 228.
[0027] Cooled mixed refrigerant stream 138 is separated in phase
separator 140 into a liquid mixed refrigerant stream 142 and a
vapor mixed refrigerant stream 144. Liquid mixed refrigerant stream
142 is sub-cooled in the cryogenic heat exchanger (MCHE) 146
producing stream 147. Stream 147 may then be reduced in pressure
through isenthalpic valve 148 producing stream 149. Stream 149 may
then be vaporized in the shell side of the MCHE 146 to provide
cooling to tubeside streams 142, 144,150.
[0028] Vapor mixed refrigerant steam 144 is condensed and
sub-cooled in the MCHE 146 to produce stream 151. Stream 151 may
then be reduced in pressure through isenthalpic valve 152 to
produce stream 153. Stream 153 may then be vaporized in the shell
side of the MCHE 146 to provide cooling to tubeside streams 142,
144, 150.
[0029] The cooled natural gas feed stream 150 may enter the MCHE
146 where it is further cooled producing product stream 166 that
may be, for example, liquid natural gas (LNG).
[0030] Low pressure mixed refrigerant stream 145 exiting the MCHE
146 is compressed in the low pressure mixed refrigerant compressor
154 to produce stream 155. It should be noted that the refrigerant
compressors of all of the exemplary embodiments may include one or
more intercoolers and compressor casings. For example, mixed
refrigerant compressor 154 may include one or more intercoolers and
at least one compressor casing. Intercoolers and aftercoolers use
an ambient heat sink (air or water) to reject compression heat to
the environment.
[0031] Stream 155 is cooled in intercooler 156 to produce stream
157. Stream 157 is further compressed in the medium pressure mixed
refrigerant compressor 158 to produce stream 159. Stream 159 is
cooled in intercooler 160 to produce stream 161. Stream 161 is
further compressed in high pressure mixed refrigerant compressor
162 to produce stream 163. Stream 163 is cooled in aftercooler 164
to be recycled back as original mixed refrigerant stream 104.
[0032] The exemplary embodiment illustrated in FIG. 1 shows how the
power supplied to the refrigeration compressors 118, 126, 154, 158,
162 are provided by two equal sized directly connected gas turbines
180, 182. For example, mixed refrigerant compressors 154, 158 are
driven by gas turbine driver 180 while mixed refrigerant compressor
160 and the propane compressors 118, 126 are driven by gas turbine
driver 182. In this exemplary embodiment, the design pressure level
between the mixed refrigerant compressors 158 and 162 may be chosen
such that the work required by the two gas turbine drivers 180, 182
is essentially equal. The gas turbine drivers in all exemplary
embodiments may be single-shaft gas turbines or multi-shaft gas
turbines, for example.
[0033] This exemplary embodiment is independent of the method used
to power the refrigeration compressors 118, 126, 154, 158 and 162.
The refrigeration compressors 118, 126, 154, 158 and 162, and the
refrigeration compressors of the other exemplary embodiments may be
driven by one or more gas turbines, electric motors, steam
turbines, or a combination of different drivers. As illustrated in
FIG. 1, the gas turbines 180, 182 may include starter/helper
electric motors 184, 186 respectively to assist in starting the gas
turbines 180, 182 and optimally, to provide additional power to
assist the gas turbines 180, 182, or to generate power for
exportation into the power grid when excess power is available from
the gas turbines. Moreover, for the exemplary embodiment
illustrated in FIG. 1, and all other exemplary embodiments
disclosed, the order of the compressor bodies and the
starter/helper electric motors coupled to each driver is not fixed
and may be manipulated/altered pursuant to any system requirements,
maintenance requirements, and/or plant design requirements. For
example, starter/helper electric motor 186 in FIG. 1 may be
positioned away from and not adjacent to driver 182 (i.e., at the
opposite end of the driver string). The positions of the compressor
bodies 118, 126, 162 may also be exchanged.
[0034] FIG. 3 illustrates another exemplary embodiment 300 where
the propane compressors 318, 326 are powered by different drivers
380, 382 respectively. In this exemplary embodiment, the power
demand from the equivalent gas turbine drivers 380, 382 may be
balanced by adjustment of the discharge pressure of low pressure
mixed refrigerant compressor 354.
[0035] As illustrated in the exemplary embodiment 300 in FIG. 3,
cooling of the natural gas feed stream 302 is performed in unit
306. Like unit 106 of FIG. 1, unit 306 may comprise a series of
heat exchangers, valves, and separators as illustrated in FIG. 2A.
Natural gas feed stream 302 is cooled by indirect heat exchange to
ultimately produce cooled stream 350. The evaporation of propane at
the four pressures results in four propane vapor streams 310, 312,
314, 316 that may then be compressed in compressor 318. The
resulting compressed stream 320 may then be condensed in propane
condenser 322, producing liquid stream 324 for reintroduction into
the series of propane evaporators as shown in FIG. 2A.
[0036] Cooling of the mixed refrigerant stream 304 is performed in
unit 308. Unit 308 may also comprise a series of heat exchangers,
valves, and separators as illustrated in FIG. 2B. The mixed
refrigerant stream 304 may also be cooled by indirect heat exchange
to ultimately produce cooled stream 338. The evaporation of propane
at the four pressures results in four propane vapor streams 330,
332, 334, 336 that may then be compressed in compressor 326. The
resulting compressed stream 327 may then be condensed in propane
condenser 328, producing liquid stream 329 for reintroduction into
the series of propane evaporators as shown in FIG. 2B.
[0037] Again cooled mixed refrigerant stream 338 is separated in
phase separator 340 into a liquid mixed refrigerant stream 342 and
a vapor mixed refrigerant stream 344. Liquid mixed refrigerant
stream 342 is sub-cooled in the cryogenic heat exchanger (MCHE) 346
producing stream 347. Stream 347 may then be reduced in pressure
through isenthalpic valve 348 producing stream 349. Stream 349 may
then be vaporized in the shell side of the MCHE 346 to provide
cooling to tubeside streams 342, 344, 350.
[0038] Vapor mixed refrigerant steam 344 is condensed and
sub-cooled in the MCHE 346 to produce stream 351. Stream 351 may
then be reduced in pressure through isenthalpic valve 352 to
produce stream 353. Stream 353 may then be vaporized in the shell
side of the MCHE 346 to provide cooling to tubeside streams 342,
344, 350.
[0039] The cooled natural gas feed stream 350 may enter the MCHE
346 where it is further cooled producing product stream 366 that
may be, for example, liquid natural gas (LNG).
[0040] Low pressure mixed refrigerant stream 345 exiting the MCHE
346 is compressed in the low pressure refrigerant compressor 354 to
produce stream 355. Stream 355 is cooled in intercooler 356 to
produce stream 357. Stream 357 is further compressed in the high
pressure refrigerant compressor 362 to produce stream 363. Stream
363 is cooled in aftercooler 364 to be recycled back as original
mixed refrigerant stream 304.
[0041] Power is supplied to the refrigeration compressors 318, 326,
354, 362 by two equal sized directly connected gas turbines 380,
382. As illustrated in FIG. 3, the gas turbines 380, 382 may
include starter/helper electric motors 384, 386 respectively to
assist in starting the gas turbines 380, 382 and optimally, to
provide additional power to assist the gas turbines 380, 382, or
for exportation into the power grid when excess power is available
from the gas turbines.
[0042] FIG. 4 illustrates another exemplary embodiment 400 where
the position of compressors 418, 426 of FIG. 3 may be swapped such
that one of the drivers provides power to the propane compressor
418 and the high pressure refrigerant compressor 462, while the
other driver provides power to the propane compressor 426 and the
low pressure refrigerant compressor 454.
[0043] As illustrated in the exemplary embodiment 400 in FIG. 4,
cooling of the natural gas feed stream 402 is performed in unit
406. Like unit 106 of FIG. 1, unit 406 may comprise a series of
heat exchangers, valves, and separators as illustrated in FIG. 2A.
Natural gas feed stream 402 is cooled by indirect heat exchange to
ultimately produce cooled stream 450. The evaporation of propane at
the four pressures results in four propane vapor streams 410, 412,
414, 416 that may then be compressed in compressor 418. The
resulting compressed stream 420 may then be condensed in propane
condenser 422, producing liquid stream 424 for reintroduction into
the series of propane evaporators as shown in FIG. 2A.
[0044] Cooling of the mixed refrigerant stream 404 is performed in
unit 408. Unit 408 may also comprise a series of heat exchangers,
valves, and separators as illustrated in FIG. 2B. The mixed
refrigerant stream 404 may also be cooled by indirect heat exchange
to ultimately produce cooled stream 438. The evaporation of propane
at the four pressures results in four propane vapor streams 430,
432, 434, 436 that may then be compressed in compressor 426. The
resulting compressed stream 427 may then be condensed in propane
condenser 428, producing liquid stream 429 for reintroduction into
the series of propane evaporators as shown in FIG. 2B.
[0045] Again cooled mixed refrigerant stream 438 is separated in
phase separator 440 into a liquid mixed refrigerant stream 442 and
a vapor mixed refrigerant stream 444. Liquid mixed refrigerant
stream 442 is sub-cooled in the cryogenic heat exchanger (MCHE) 446
producing stream 447. Stream 447 may then be reduced in pressure
through isenthalpic valve 448 producing stream 449. Stream 449 may
then be vaporized in the shell side of the MCHE 446 to provide
cooling to tubeside streams 442, 444, 450.
[0046] Vapor mixed refrigerant steam 444 is condensed and
sub-cooled in the MCHE 446 to produce stream 451. Stream 451 may
then be reduced in pressure through isenthalpic valve 452 to
produce stream 453. Stream 453 may then be vaporized in the shell
side of the MCHE 446 to provide cooling to tubeside streams 442,
444, 450.
[0047] The cooled natural gas feed stream 450 may enter the MCHE
446 where it is further cooled producing product stream 466 that
may be, for example, liquid natural gas (LNG).
[0048] Low pressure mixed refrigerant stream 445 exiting the MCHE
446 is compressed in the low pressure refrigerant compressor 454 to
produce stream 455. Stream 455 is cooled in intercooler 456 to
produce stream 457. Stream 457 is further compressed in high
pressure refrigerant compressor 462 to produce stream 463. Stream
463 is cooled in aftercooler 464 to be recycled back as original
mixed refrigerant stream 404.
[0049] Power is supplied to the refrigeration compressors 418, 426,
454, 462 by two equal sized directly connected gas turbines 480,
482. As illustrated in FIG. 4, the gas turbines 480, 482 may
include starter/helper electric motors 484, 486 respectively to
assist in starting the gas turbines 480, 482 and optimally, to
provide additional power to assist the gas turbines 480, 482, or
for exportation into the power grid when excess power is available
from the gas turbines.
[0050] FIG. 5 illustrates yet another exemplary embodiment 500 as
applied to a three loop refrigeration system. In this exemplary
embodiment 500, unit 506 precools a third refrigerant stream 503 in
addition to the natural gas feed stream 502. Like unit 106 of FIG.
1, unit 506 may comprise a series of heat exchangers, valves, and
separators as illustrated in FIG. 2A. Natural gas feed stream 502
is cooled by indirect heat exchange to ultimately produce cooled
stream 550. The evaporation of propane at the four pressures
results in four propane vapor streams 510, 512, 514, 516 that may
then be compressed in compressor 518. The resulting compressed
stream 520 may then be condensed in propane condenser 522,
producing liquid stream 524 for reintroduction into the series of
propane evaporators as shown in FIG. 2A.
[0051] Cooling of the mixed refrigerant stream 504 is performed in
unit 508. Unit 508 may also comprise a series of heat exchangers,
valves, and separators as illustrated in FIG. 2B. The mixed
refrigerant stream 504 may also be cooled by indirect heat exchange
to ultimately produce cooled stream 538. The evaporation of propane
at the four pressures results in four propane vapor streams 530,
532, 534, 536 that may then be compressed in compressor 526. The
resulting compressed stream 527 may then be condensed in propane
condenser 528, producing liquid stream 529 for reintroduction into
the series of propane evaporators as shown in FIG. 2B.
[0052] Cooled mixed refrigerant stream 538 is subcooled in the
cryogenic heat exchanger (MCHE) 546 producing stream 547. Stream
547 may then be reduced in pressure through isenthalpic valve 548
producing stream 549. Stream 549 may then be vaporized in the shell
side of the MCHE 546 to provide cooling to tubeside streams 505,
538, and 550.
[0053] Cooled mixed refrigerant stream 505 may also be subcooled
and liquefied in MCHE 546 producing stream 569 then subcooled in
exchanger 568 producing stream 551. Exchanger 568 may be a wound
coil type exchanger, for example. The resulting stream 551 may then
be reduced in pressure through isenthalpic valve 552 to produce
stream 553. Stream 553 may then be vaporized in exchanger 568 to
provide refrigeration for subcooling both the feed gas stream
(entering as stream 567 and exiting as 566) and the third
refrigerant stream 569. After vaporization and warming, third
refrigerant stream 553 exits exchanger 568 as stream 593 and is
then compressed by compressor 594 to produce stream 595. Stream 595
is then cooled in the mixed refrigerant intercooler 596 to produce
stream 597. Stream 597 is compressed in compressor 598 to produce
stream 599. Stream 599 is then cooled in mixed refrigerant
aftercooler 501 to be recycled back as original stream 503.
[0054] The cooled natural gas feed stream 550 may enter the MCHE
546 where it is further cooled producing stream 567. Stream 567 may
then be subcooled in exchanger 568 to produce product stream 566
that may be, for example, liquid natural gas (LNG).
[0055] Low pressure mixed refrigerant stream 545 exiting the MCHE
546 is compressed in the low pressure refrigerant compressor 554 to
produce stream 555. Stream 555 is cooled in intercooler 556 to
produce stream 557. Stream 557 is further compressed in high
pressure refrigerant compressor 558 to produce stream 559. Stream
559 is cooled in aftercooler 564 to be recycled back as original
mixed refrigerant stream 504.
[0056] Power is supplied to the refrigeration compressors 518, 526,
554, 558, 594, 598 by three equal sized directly connected gas
turbines 580, 582, 592. As illustrated in FIGS. 1, 3, and 4, the
gas turbines may include starter/helper electric motors (not shown
in this embodiment) to assist in starting the gas turbines and
optimally, to provide additional power to assist the gas turbines,
or for exportation into the power grid when excess power is
available from the gas turbines.
[0057] FIG. 6 illustrates yet another exemplary embodiment 600 as
applied to another three loop refrigeration system. In this
exemplary embodiment 600, unit 606 precools the natural gas feed
stream 602 only. Like unit 106 of FIG. 1, unit 606 may comprise a
series of heat exchangers, valves, and separators as illustrated in
FIG. 2A. Natural gas feed stream 602 is cooled by indirect heat
exchange to ultimately produce cooled stream 650. The evaporation
of propane at the four pressures results in four propane vapor
streams 610, 612, 614, 616 that may then be compressed in
compressor 618. The resulting compressed stream 620 may then be
condensed in propane condenser 622, producing liquid stream 624 for
reintroduction into the series of propane evaporators as shown in
FIG. 2A.
[0058] In this exemplary embodiment, both mixed refrigerant streams
603, 604 are cooled in unit 608. Unit 608 may also comprise a
series of heat exchangers, valves, and separators as illustrated in
FIG. 2B. The mixed refrigerant streams 603, 604 may also be cooled
by indirect heat exchange to ultimately produce cooled streams 605,
638. The evaporation of propane at the four pressures results in
four propane vapor streams 630, 632, 634, 636 that may then be
compressed in compressor 626. The resulting compressed stream 627
may then be condensed in propane condenser 628, producing liquid
stream 629 for reintroduction into the series of propane
evaporators as shown in FIG. 2B.
[0059] Cooled mixed refrigerant stream 638 is subcooled in the
cryogenic heat exchanger (MCHE) 646 producing stream 647. Stream
647 may then be reduced in pressure through isenthalpic valve 648
producing stream 649. Stream 649 may then be vaporized in the shell
side of the MCHE 646 to provide cooling to tubeside streams 605,
638, and 650.
[0060] Cooled mixed refrigerant stream 605 may also be subcooled
and liquefied in MCHE 646 producing stream 669 then subcooled in
exchanger 668 producing stream 651. Exchanger 668 may be a wound
coil type exchanger, for example. The resulting stream 651 may then
be reduced in pressure through isenthalpic valve 652 to produce
stream 653. Stream 653 may then be vaporized in exchanger 668 to
provide refrigeration for subcooling both the feed gas stream
(entering as stream 667 and exiting as 666) and the third
refrigerant stream 669. After vaporization and warming, third
refrigerant stream 653 exits exchanger 668 as stream 693 and is
then compressed by compressor 694 to produce stream 695. Stream 695
is then cooled in the mixed refrigerant intercooler 696 to produce
stream 697. Stream 697 is compressed in compressor 698 to produce
stream 699. Stream 699 is then cooled in mixed refrigerant
aftercooler 601 to be recycled back as original stream 603.
[0061] The cooled natural gas feed stream 650 may enter the MCHE
646 where it is further cooled producing stream 667. Stream 667 may
then be subcooled in exchanger 668 to produce product stream 666
that may be, for example, liquid natural gas (LNG).
[0062] Low pressure mixed refrigerant stream 645 exiting the MCHE
646 is compressed in the low pressure refrigerant compressor 654 to
produce stream 655. Stream 655 is cooled in intercooler 656 to
produce stream 657. Stream 657 is further compressed in the high
pressure refrigerant compressor 658 to produce stream 659. Stream
659 is cooled in aftercooler 664 to be recycled back as original
mixed refrigerant stream 604.
[0063] Power is supplied to the refrigeration compressors 618, 626,
654, 658, 694, 698 by three equal sized directly connected gas
turbines 680, 682, 692. As illustrated in FIGS. 1, 3, and 4, the
gas turbines may include starter/helper electric motors (not shown
in this embodiment) to assist in starting the gas turbines and
optimally, to provide additional power to assist the gas turbines,
or for exportation into the power grid when excess power is
available from the gas turbines.
[0064] FIG. 7A illustrates another exemplary embodiment 700A as
applied to yet another three loop refrigeration system. In this
exemplary embodiment 700A, unit 706 precools the natural gas feed
stream 702 and the mixed refrigerant stream 704. Like unit 106 of
FIG. 1, unit 706 may comprise a series of heat exchangers, valves,
and separators as illustrated in FIG. 2A. Natural gas feed stream
702 and mixed refrigerant stream 704 is cooled by indirect heat
exchange to ultimately produce cooled streams 750, 738. The
evaporation of propane at the four pressures results in four
propane vapor streams 710, 712, 714, 716 that may then be
compressed in compressor 718. The resulting compressed stream 720
may then be condensed in propane condenser 722, producing liquid
stream 724 for reintroduction into the series of propane
evaporators as shown in FIG. 2A.
[0065] In this exemplary embodiment, only mixed refrigerant stream
703 is cooled in unit 708. Unit 708 may also comprise a series of
heat exchangers, valves, and separators as illustrated in FIG. 2B.
The mixed refrigerant stream 703 is cooled by indirect heat
exchange to ultimately produce cooled streams 705. The evaporation
of propane at the four pressures results in four propane vapor
streams 730, 732, 734, 736 that may then be compressed in
compressor 726. The resulting compressed stream 727 may then be
condensed in propane condenser 728, producing liquid stream 729 for
reintroduction into the series of propane evaporators as shown in
FIG. 2B.
[0066] Cooled mixed refrigerant stream 738 is subcooled in the
cryogenic heat exchanger (MCHE) 746 producing stream 747. Stream
747 may then be reduced in pressure through isenthalpic valve 748
producing stream 749. Stream 749 may then be vaporized in the shell
side of the MCHE 746 to provide cooling to tubeside streams 705,
738, and 750.
[0067] Cooled mixed refrigerant stream 705 may also be subcooled
and liquefied in MCHE 746 producing stream 769 then subcooled in
exchanger 768 producing stream 751. Exchanger 768 may be a wound
coil type exchanger, for example. The resulting stream 751 may then
be reduced in pressure through isenthalpic valve 752 to produce
stream 753. Stream 753 may then be vaporized in exchanger 768 to
provide refrigeration for subcooling both the feed gas stream
(entering as stream 767 and exiting as 766) and the third
refrigerant stream 769. After vaporization and warming, third
refrigerant stream 753 exits exchanger 768 as stream 793 and is
then compressed by compressor 794 to produce stream 795. Stream 795
is then cooled in the mixed refrigerant intercooler 796 to produce
stream 797. Stream 797 is compressed in compressor 798 to produce
stream 799. Stream 799 is then cooled in mixed refrigerant
aftercooler 701 to be recycled back as original stream 703.
[0068] The cooled natural gas feed stream 750 may enter the MCHE
746 where it is further cooled producing stream 767. Stream 767 may
then be subcooled in exchanger 768 to produce product stream 766
that may be, for example, liquid natural gas (LNG).
[0069] Low pressure mixed refrigerant stream 745 exiting the MCHE
746 is compressed in the low pressure refrigerant compressor 754 to
produce stream 755. Stream 755 is cooled in intercooler 756 to
produce stream 757. Stream 757 is further compressed in the high
pressure refrigerant compressor 758 to produce stream 759. Stream
759 is cooled in aftercooler 764 to be recycled back as original
mixed refrigerant stream 704.
[0070] Power is supplied to the refrigeration compressors 718, 726,
754, 758, 794, 798 by three equal sized directly connected gas
turbines 780, 782, 792. As illustrated in FIGS. 1, 3, and 4, the
gas turbines may include starter/helper electric motors (not shown
in this embodiment) to assist in starting the gas turbines and
optimally, to provide additional power to assist the gas turbines,
or for exportation into the power grid when excess power is
available from the gas turbines.
[0071] FIG. 7B illustrates yet another exemplary embodiment 700B
similar to 700A, however, in this exemplary embodiment 700B, unit
706 precools the natural gas feed stream 702 and the mixed
refrigerant stream 704 through indirect heat exchange with a mixed
refrigerant stream in a two-stage mixed refrigerant precooling
system. While FIG. 7B discloses use of a two-stage mixed
refrigerant precooling system, the precooling may be performed
using a single-stage mixed refrigerant precooling system, or mixed
refrigerant precooling systems with greater than two stages, for
example. Additionally, a mixed refrigerant precooling system may be
interchanged with the propane precooling systems disclosed in any
of the exemplary embodiments.
[0072] FIGS. 8A and 8B illustrate exemplary units 706 and 708 shown
in FIG. 7B. Unit 706 may comprise two heat exchangers 810, 812
where streams 702, 704, and at least a portion of stream 724 are
cooled through indirect heat exchange against stream 713 in heat
exchanger 810. Stream 724 enters heat exchanger 810 and is cooled
producing stream 830. Stream 830 is split into two streams 831, 832
where stream 831 is further cooled in heat exchanger 812 while
stream 832 is let down in pressure across isenthalpic valve 814 to
produce stream 833. Stream 833 then enters heat exchanger 810 to
provide cooling to streams 702, 704, 724 and exits the heat
exchanger 810 as stream 713.
[0073] After stream 831 is cooled in heat exchanger 812 to produce
stream 834 and let down in pressure across isenthalpic valve 816,
the resulting stream 835 is introduced into heat exchanger 812 to
provide further cooling for resultant streams 738, 750, 834.
[0074] Unit 708 may comprise two heat exchangers 818, 820 where
streams 703, 729 are cooled through indirect heat exchange against
stream 733 in heat exchanger 818. Stream 729 enters heat exchanger
818 and is cooled producing stream 840. Stream 840 is split into
two streams 841, 842 where stream 841 is further cooled in heat
exchanger 820 while stream 842 is let down in pressure across
isenthalpic valve 822 to produce stream 843. Stream 843 then enters
heat exchanger 818 to provide cooling to streams 703, 729 and exits
the heat exchanger 818 as stream 733.
[0075] After stream 841 is cooled in heat exchanger 820 to produce
stream 844 and let down in pressure across isenthalpic valve 824,
the resulting stream 845 is introduced into heat exchanger 820 to
provide further cooling for resultant streams 705, 844.
[0076] Heat exchangers 810, 812, 818, 820 may be wound-coil heat
exchangers, plate-and-fin brazed aluminum (core) type heat
exchangers, or shell and tube heat exchangers, for example. Heat
exchangers 810, 812 may be combined into a single heat exchanger,
for example. Heat exchangers 818, 820 may also be combined into a
single heat exchanger, for example. Finally, heat exchangers 810,
812, 818, 820 may be combined into a single heat exchanger, for
example. Heat exchangers 810, 812, 818, 820 may accept two or more
load streams, for example.
[0077] Pre-cooling in units 106, 108 may provide, for example,
enough cooling to feed stream 102 and liquefaction refrigerant
stream 104 such that the temperatures of streams 150 and 138 may
reach +60.degree. F. to as low as -100.degree. F. before further
cooling in the MCHE 146. The same cooling ranges may be achieved in
FIGS. 3-7B. In one embodiment, for example, propane may be used as
the pre-cooling refrigerant to reach the temperature range of
+20.degree. F. to -40.degree. F.
[0078] The isenthalpic valves 148, 152 (and the corresponding
isenthalpic valves in FIGS. 3-7B) may optionally be replaced by
work extracting liquid turbines, for example, to improve
efficiency. Additionally, propane condensers 122, 128 (and the
corresponding propane condensers in FIGS. 3-7A) may be ambient heat
sink coolers used to condense, desuperheat, and/or optimally
subcool precooling refrigerant, for example.
EXAMPLE
[0079] The following example is based on a computer simulation of
FIGS. 1, 2A, and 2B as applied to a propane precooled mixed
refrigerant process. As in FIG. 1, the natural gas feed stream 102
entered unit 106 after pretreatment, including the removal of
moisture (H.sub.2O), carbon dioxide (CO.sub.2), sulfur dioxide
(SO.sub.2), mercury, and other heavy components, including, but not
limited to, benzene, ethylbenzene, and toluene, if they exist in
the natural gas feed stream 102 in concentrations that would lead
to freezing in the MCHE 146. The pretreated natural gas feed stream
102 was at 35.degree. C. and 40 bar absolute and had a flow rate of
12,260 kg-mole/hr. Natural gas feed stream 102 was cooled by
indirect heat exchange in a series of propane evaporators 202, 204,
206, 208 (illustrated in FIG. 2A) that operate at successively
lower pressures of 7.16 bar, 4.25 bar, 2.54 bar and 1.47 bar, where
propane evaporator 202 is at the highest pressure and propane
evaporator 208 is at the lowest pressure. The evaporation of
propane at the four pressures resulted in four propane vapor
streams 110, 112, 114, 116 that were then compressed in compressor
118. Resulting stream 120 (at 16.2 bar, and 10,930 kgmole/hr) was
then condensed in propane condenser 122 using an ambient heat sink
(air or water), producing liquid stream 124.
[0080] The natural gas feed stream 102 was precooled by the propane
to -22.5.degree. C. Resulting cooled stream 150 was then cooled and
liquefied in MCHE 146 by vaporizing mixed refrigerant producing
liquid natural gas (LNG) stream 166 at -163.3.degree. C.
[0081] The mixed refrigerant stream 104 had a molar composition as
follows:
TABLE-US-00001 TABLE I Component Mole Composition (%) Nitrogen 12
Methane 38 Ethane 42 Propane 8
[0082] The mixed refrigerant stream 104 was at 35.degree. C. and 62
bar absolute and had a flow rate of 50,250 kg-mole/hr. The mixed
refrigerant stream 104 was cooled by indirect heat exchange in a
series of propane evaporators 222, 224, 226, 228 (illustrated in
FIG. 2B) that operate at successively lower pressures of 7.16 bar
absolute, 4.25 bar, 2.54 bar and 1.47 bar where propane evaporator
203 is the highest and propane evaporator 209 is the lowest. The
evaporation of propane at the four pressures results in four
propane vapor streams 130, 132, 134, 138 which are then compressed
in compressor 126. Resulting stream 127 (at 16.2 bar absolute and
31,600 kgmole/hr) is condensed in propane condenser 128 using an
ambient heat sink (air or water), producing liquid stream 129.
[0083] The precooled mixed refrigerant stream 138 is then separated
into liquid stream 142 and vapor stream 144 in phase separator 140.
Liquid stream 142 is then subcooled to -125.degree. C., flashed
isenthalpically through valve 148, and then vaporized in the shell
side of exchanger 146 to provide cooling to the tubeside streams
142, 144, 150. Vapor stream 144 is liquefied, subcooled to a
temperature of -163.degree. C., flashed isenthalpically through
valve 152, and then vaporized and warmed in the shell side of
exchanger 146 to provide cooling to the tubeside streams 142, 144,
150. After vaporization and warming, the combined mixed refrigerant
stream 145 exits the MCHE 146 at a temperature of -32.7.degree. C.
and a pressure of 4.14 bar absolute. The combined mixed refrigerant
stream 154 is then compressed in three stages of compressors 156,
158, 160 back to a pressure of 62 bar absolute, completing the
loop.
Comparison with U.S. Pat. No. 6,962,060
[0084] Computer simulations of the exemplary embodiment illustrated
in FIG. 1 were performed on the same basis as the simulation of a
propane precooled mixed refrigerant process utilizing the
precooling arrangement of U.S. Pat. No. 6,962,060.
[0085] Results for the simulations are listed in Table II below.
For both simulations, the same propane low pressure suction
pressure was assumed and two compressor casings were required. For
both simulations, preliminary sizing calculations for the
compressors were performed. In the case of the exemplary embodiment
illustrated in FIG. 1, the compressor casings 118 and 126 were
smaller in diameter and had lower volumetric flow rates translating
into lower cost. In addition, depending on the vendor and the scale
of the plant, construction of large diameter impellers and casings
may not have been feasible, thus, the solution utilizing the prior
art may have been more limited in scale-up potential.
[0086] As illustrated in Table II, the exemplary embodiment of FIG.
1 allows more optimal and feasible compressor designs than the
system disclosed in U.S. Pat. No. 6,962,061 using the same number
of compressor casings and providing the same pre-cooling service.
This is achieved by segregating the heat loads requiring
pre-cooling refrigeration into two independent systems.
TABLE-US-00002 TABLE II U.S. Pat. Exemplary No. Embodiment in
6,962,060 FIG. 1 Precooling -30.2 -30.2 Temperature (.degree. C.)
Liquid Natural Gas 490,000 490,000 Production (kg/h) Compressor 1
Identifier Compressor 43 Compressor 126 Maximum Impeller 55 50
Diameter (inches) Maximum Volume 149,000 119,000 Flow Rate
(m.sup.3/hr) Compressor 2 Identifier Compressor 49 Compressor 118
Maximum Impeller 52 51 Diameter (inches) Maximum Volume 78,000
57,000 Flow Rate (m.sup.3/hr)
[0087] While aspects of the present invention has been described in
connection with the preferred embodiments of the various figures,
it is to be understood that other similar embodiments may be used
or modifications and additions may be made to the described
embodiment for performing the same function of the present
invention without deviating therefrom. Therefore, the claimed
invention should not be limited to any single embodiment, but
rather should be construed in breadth and scope in accordance with
the appended claims.
* * * * *