U.S. patent application number 17/389744 was filed with the patent office on 2022-02-03 for large liquid oxygen and liquefied natural gas production process.
The applicant listed for this patent is L'Air Liquide, Societe Anonyme pour l'Etude et l'Exploitation des Procedes Georges Claude. Invention is credited to Alain GUILLARD, Michael A. TURNEY.
Application Number | 20220034584 17/389744 |
Document ID | / |
Family ID | |
Filed Date | 2022-02-03 |
United States Patent
Application |
20220034584 |
Kind Code |
A1 |
TURNEY; Michael A. ; et
al. |
February 3, 2022 |
LARGE LIQUID OXYGEN AND LIQUEFIED NATURAL GAS PRODUCTION
PROCESS
Abstract
A process for co-producing a liquid oxygen and a liquefied
hydrocarbon stream, including introducing a gaseous hydrocarbon
stream and a gaseous nitrogen stream into a liquefier, thereby
producing a liquefied hydrocarbon stream and a liquid nitrogen
stream, liquefying a gaseous oxygen stream, wherein at least a
portion of the required refrigeration is obtained from the liquid
nitrogen stream. Wherein the liquefied hydrocarbon stream and the
liquefied gaseous oxygen stream have mass flow rates. The liquid
oxygen stream may be produced in an aft separation unit, wherein at
least a portion of the required refrigeration is obtained from the
liquid nitrogen stream.
Inventors: |
TURNEY; Michael A.;
(Houston, TX) ; GUILLARD; Alain; (Houston,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
L'Air Liquide, Societe Anonyme pour l'Etude et l'Exploitation des
Procedes Georges Claude |
Paris |
|
FR |
|
|
Appl. No.: |
17/389744 |
Filed: |
July 30, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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63058898 |
Jul 30, 2020 |
|
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International
Class: |
F25J 1/02 20060101
F25J001/02; F25J 1/00 20060101 F25J001/00 |
Claims
1. A process for co-producing a liquid oxygen and a liquefied
hydrocarbon stream, comprising: introducing a gaseous hydrocarbon
stream and a gaseous nitrogen stream into a liquefier, thereby
producing a liquefied hydrocarbon stream and a liquid nitrogen
stream, liquefying a gaseous oxygen stream, wherein at least a
portion of he required refrigeration is obtained from the liquid
nitrogen stream, wherein the liquefied hydrocarbon stream and the
liquefied gaseous oxygen stream have mass flow rates.
2. The process of claim 1, wherein the ratio of mass flow rates of
the liquefied gaseous oxygen stream and the liquefied hydrocarbon
stream is between 2 to 5.
3. The process of claim 1, wherein the ratio of mass flow rates of
the liquefied gaseous oxygen stream and the liquefied hydrocarbon
stream is between 3 to 4.
4. The process of claim 1, wherein the liquefier uses a dual
refrigerant liquefaction process, comprising a first refrigerant
and a secondary refrigerant.
5. The process of claim 4, wherein the first refrigerant is
nitrogen or neon or a mixture of neon and nitrogen.
6. The process of claim 4, wherein the secondary refrigerant is a
hydrocarbon mixed refrigerant.
7. A process for co-producing a liquid oxygen and a liquefied
hydrocarbon stream, comprising: introducing a gaseous hydrocarbon
stream and a gaseous nitrogen stream in a liquefier, thereby
producing a liquefied hydrocarbon stream and a liquid nitrogen
stream, producing a liquid oxygen stream in an air separation unit,
wherein at least a portion of a required refrigeration is obtained
from the liquid nitrogen stream, wherein the liquefied hydrocarbon
stream, the liquid nitrogen stream, and the liquid oxygen stream
have mass flow rates.
8. The process of claim 7. wherein the ratio of mass flow rates of
the liquid oxygen stream and the liquefied hydrocarbon stream is
between 2 to 5.
9. The process of claim 7, wherein the ratio of mass flow rates of
the liquid oxygen stream and the liquefied hydrocarbon stream is
between 3 to 4.
10. The process of claim 7, wherein the ratio of mass flow rates
the liquid nitrogen stream to the liquid oxygen stream is 0.5 to
1.1.
11. The process of claim 7, wherein the liquefier uses a dual
refrigerant liquefaction process, comprising a first refrigerant
and a secondary refrigerant.
12. The process of claim 11, wherein the first refrigerant is
nitrogen or neon or a mixture of neon and nitrogen.
13. The process of claim 11, wherein the secondary refrigerant is
hydrocarbon mixed refrigerant.
14. The process of claim 7. wherein at least a portion of the
refrigeration required to liquefy the oxygen is from an auxiliary
refrigeration produced within the air separation unit.
15. The process of claim 14, wherein the auxiliary refrigeration is
produced within the air separation unit with a main air compressor
and/or a booster air compressor.
16. The process of claim 15, wherein the auxiliary refrigeration is
produced from at least 10% of the combined main air compressor
and/or booster air compressor energy.
17. The process of claim 7. where the pressurized gaseous oxygen
and/or gaseous nitrogen stream are produced by pumping of liquid
and vaporizing.
18. The process of claim 7, wherein at least a portion of the
liquid oxygen stream is subcooled by heat exchange in the air
separation unit with a nitrogen stream.
19. The process of claim 7, wherein the air separation unit
produces both a liquid oxygen stream with a mass flowrate and a
gaseous oxygen stream with a mass flowrate, the liquid oxygen
stream mass flowrate is added to the gaseous oxygen stream mass
flowrate to produce a total oxygen mass flowrate, and wherein at
least 90% of the of the total oxygen mass flowrate is liquid
oxygen.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn. 119 (a) and (b) to U.S. Provisional Patent
Application No. 63/058,898, filed Jul. 30, 2020, the entire
contents of which are incorporated herein by reference.
BACKGROUND
[0002] There is demand for large quantities of low-cost liquid
oxygen (LOX) and liquefied natural gas (LNG) as rocket fuel for
both the current and the emerging space industry. Oxygen and
purified natural gas are both used due to their different fuel
properties to provide different thrust, etc. in different specific
stages of the rocket and their liquid forms are used due to higher
densities for storage on the rocket. The resulting requirement for
staging of one such demand is in the range of LOX/LNG mass flow
ratio of between 3 and 4.
[0003] There are several methods are known for production of LOX
and LNG in the art. First, these two streams are typically produced
separately and independently liquefied. As an example, an air
separation unit (ASU) produces pressurized gaseous oxygen (GOX) and
a nitrogen liquefier cycle produces liquefied nitrogen (LIN) which
is vaporized by indirect heat exchanges with natural gas (NG) and
liquid oxygen (LOX) in independent systems yielding LOX and
liquefied natural gas (LNG). This method is intensive in terms of
both operating expense (OPEX) and capital expense (CAPEX) due to
energy and heat exchanges needed to pressurize O2 and liquefy and
re-vaporize LIN.
[0004] Alternatively the LNG can be independently liquefied
yielding an efficient OPEX of approximately 0.28 kQ/Nm3 for LNG.
However, this has a very high CAPEX due to the need of a separate
and independent refrigeration cycle which may be mixed refrigerant,
N2 expansion.
[0005] Another known method is to produce the LOX directly from the
ASU with refrigeration provided by LIN from a N2 cycle liquefier to
the ASU. This yields more efficient OPEX of approximately 0.51
kW/Nm3 for LIN as it removes the gaseous O2 compression step and
indirect heat transfer between vaporizing LIN to condensing LOX.
However, this does not solve the CAPEX penalties of requiring a
separate independent LNG plant.
SUMMARY
[0006] A process for co-producing a liquid oxygen and a liquefied
hydrocarbon stream, including introducing a gaseous hydrocarbon
stream and a gaseous nitrogen stream into a liquefier, thereby
producing a liquefied hydrocarbon stream and a liquid nitrogen
stream, liquefying a gaseous oxygen stream, wherein at least a
portion of the required refrigeration is obtained from the liquid
nitrogen stream. Wherein the liquefied hydrocarbon stream and the
liquefied gaseous oxygen stream have mass flow rates.
[0007] A process for co-producing a liquid oxygen and a liquefied
hydrocarbon stream, including introducing a gaseous hydrocarbon
stream and a gaseous nitrogen stream in a liquefier, thereby
producing a liquefied hydrocarbon stream and a liquid nitrogen
stream, producing a liquid oxygen stream in an air separation unit,
wherein at least a portion of a required refrigeration is obtained
from the liquid nitrogen stream. Wherein the liquefied hydrocarbon
stream, the liquid nitrogen stream, and the liquid oxygen stream
have mass flow rates.
BRIEF DESCRIPTION OF THE FIGURES
[0008] For a further understanding of the nature and objects for
the present invention, reference should be made to the following
detailed description, taken in conjunction with the accompanying
drawings, in which like elements are given the same or analogous
reference numbers and wherein:
[0009] FIG. 1 is a schematic representation of a non-limiting
example of a combined ASU and LNG system as known to the art.
[0010] FIG. 2 is a schematic representation of a non-limiting
example of a basic air separation system as known to the art.
[0011] FIG. 3 is a schematic representation of non-limiting example
of liquefaction heat exchanger as known in the art.
[0012] FIG. 4 is a schematic representation of an air separation
system in accordance with one embodiment of the present
invention.
[0013] FIG. 5 is a schematic representation of a combined ASU and
LNG system in accordance with one embodiment of the present
invention.
ELEMENT NUMBERS
[0014] 101=Inlet air stream
[0015] 102=main air compressor (MAC)
[0016] 103=compressed inlet air stream
[0017] 104=front end purification
[0018] 105=purified air stream
[0019] 106=air separation unit (ASU)
[0020] 107=low-pressure nitrogen stream
[0021] 108=medium-pressure nitrogen stream
[0022] 109=liquid oxygen stream
[0023] 110=liquid oxygen storage
[0024] 111=nitrogen liquefaction heat exchanger
[0025] 112=liquid nitrogen stream
[0026] 113=export liquid nitrogen stream
[0027] 114=heat exchange
[0028] 115=gaseous nitrogen stream
[0029] 116=internal liquid nitrogen stream
[0030] 117=inlet natural gas stream
[0031] 118=liquid natural gas stream
[0032] 119=liquid natural gas storage device
[0033] 201=inlet air stream
[0034] 202=main air compressor (MAC)
[0035] 203=compressed inlet air stream
[0036] 204=front end purification unit
[0037] 205=purified inlet air stream
[0038] 206=main heat exchanger
[0039] 207=cold air stream
[0040] 208=medium-pressure distillation column
[0041] 209=oxygen-rich liquid stream
[0042] 210=nitrogen reflux stream
[0043] 211=low-pressure distillation column
[0044] 212=cold waste nitrogen stream
[0045] 213=low-pressure pure nitrogen stream
[0046] 214=liquid oxygen stream
[0047] 215=medium-pressure nitrogen stream
[0048] 216=warm medium-pressure nitrogen stream
[0049] 217=combined nitrogen reflux stream
[0050] 350=warm mixed refrigerant return steam
[0051] 351=mixed refrigerant compressor
[0052] 352=pressurized mixed refrigerant stream
[0053] 353=mixed refrigerant cooler
[0054] 354=cooled pressurized mixed refrigerant stream
[0055] 355=first pressure reducing vessel
[0056] 356=first vapor portion
[0057] 357=first liquid portion
[0058] 358=first combined mixed refrigerant stream
[0059] 359=intermediate mixed refrigerant stream
[0060] 363=intermediate mixed refrigerant stream
[0061] 364=LP nitrogen compressor
[0062] 365=warm medium-pressure nitrogen stream
[0063] 366=first nitrogen cooler
[0064] 367=cooled medium-pressure nitrogen stream
[0065] 368=combined medium-pressure nitrogen stream
[0066] 369=MP nitrogen compressor
[0067] 370=warm intermediate-pressure nitrogen stream
[0068] 371=second nitrogen cooler
[0069] 372=cooled intermediate-pressure nitrogen stream
[0070] 373=HP nitrogen compressor
[0071] 374=medium-pressure nitrogen stream
[0072] 375=first nitrogen refrigeration stream
[0073] 376=nitrogen expander
[0074] 377=expanded nitrogen stream
[0075] 378=second nitrogen refrigeration stream
[0076] 379=third pressure reducing vessel
[0077] 380=nitrogen vapor portion
[0078] 381=nitrogen liquid portion
[0079] 382=combined nitrogen stream
[0080] 383=cold nitrogen recycle stream
[0081] 384=second nitrogen recycle stream
[0082] 385=first nitrogen recycle stream
[0083] 386=mixed refrigerant pressure letdown valve
[0084] 387=nitrogen refrigeration cycle pressure letdown valve
[0085] 390=mixed refrigerant cycle
[0086] 391=nitrogen refrigeration cycle
[0087] 401=first portion of purified inlet air stream
[0088] 402=second portion of purified inlet air stream
[0089] 403=booster air compressor
[0090] 404=boosted inlet air stream
[0091] 405=first portion of boosted inlet air stream
[0092] 406=second portion of boosted inlet air stream
[0093] 407=cold boosted air stream
[0094] 408=expander
[0095] 409=expanded second portion of boosted inlet air stream
[0096] 410=cold expanded second portion of boosted inlet air
stream
[0097] 411=combined nitrogen reflux stream
[0098] 506=air separation unit (ASU)
[0099] 510=liquid oxygen storage
[0100] 511=liquefaction heat exchanger
[0101] 516=liquid nitrogen stream
[0102] 517=internal liquid nitrogen stream
[0103] 518=export liquid nitrogen stream
[0104] 519=inlet natural gas stream
[0105] 520=liquid natural gas stream
[0106] 521=liquid natural gas storage device
DESCRIPTION OF PREFERRED EMBODIMENTS
[0107] Illustrative embodiments of the invention are described
below. While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and are herein described in
detail. It should be understood, however, that the description
herein of specific embodiments is not intended to limit the
invention to the particular forms disclosed, but on the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
[0108] It will of course be appreciated that in the development of
any such actual embodiment, numerous implementation-specific
decisions must be made to achieve the developer's specific goals,
such as compliance with system-related and business-related
constraints, which will vary from one implementation to another.
Moreover, it will be appreciated that such a development effort
might be complex and time-consuming, but would nevertheless be a
routine undertaking for those of ordinary skill in the art having
the benefit of this disclosure.
[0109] The following abbreviations are used herein; mixed
refrigerant (MR), air separation unit (ASU), main air compressor
(MAC), booster air compressor (BAC), liquefied natural gas (LNG),
gaseous oxygen (GOX), liquid oxygen (LOX), liquid nitrogen (LIN),
and liquid argon (LAR).
[0110] Turning now to FIG. 1, a non-limiting example of a combined
ASU and LNG system as known to the art is described. Inlet air
stream 101 is compressed in main air compressor (MAC) 102, thereby
producing compressed inlet air stream 103. Compressed inlet air
stream 103 is then introduced into front end purification device
104, thereby producing purified air stream 105. Purified air stream
105 then enters air separation unit 106. Air separation unit 106
produces at least low-pressure nitrogen stream 107, medium-pressure
nitrogen stream 108, and liquid oxygen stream 109. Liquid oxygen
stream 109 is sent liquid oxygen storage device 110. In order to
produce the desired flowrate in liquid oxygen stream 109, it is
necessary to introduce additional refrigeration duty into the ASU,
in the form of internal liquid nitrogen stream 116.
[0111] Low-pressure nitrogen stream 107 and medium-pressure
nitrogen stream 108 are introduced into nitrogen liquefaction heat
exchanger 111. Nitrogen liquefaction heat exchanger 111 outputs at
least at liquid nitrogen stream 112. Liquid nitrogen stream 112 is
divided into export liquid nitrogen stream 113, and internal liquid
nitrogen stream 116. Export liquid nitrogen stream 113 exchanges
heat with inlet natural gas stream 117 in heat exchanger 114,
thereby producing gaseous nitrogen stream 115 and liquid natural
gas stream 118. Liquid natural gas stream 118 is sent to liquid
natural gas storage device 119.
[0112] Turning now to FIG. 2, a non-limiting example of a basic air
separation system as known to the art is described. Inlet air
stream 201 is compressed in main air compressor (MAC) 202, thereby
producing compressed inlet air stream 203. Compressed inlet air
stream 203 is then introduced into front end purification device
204, thereby producing purified inlet air stream 205. Purified
inlet air stream 205 then enters main heat exchanger 206. Inside
main heat exchanger 206, purified inlet air stream 205 indirectly
exchanges heat with at least warm waste nitrogen stream 212
(below), and medium-pressure nitrogen stream 215 (below). This
indirect heat exchange thus produces cold air stream 207, which is
introduced into medium-pressure distillation column 208.
[0113] Medium-pressure distillation column 208 produces at least
oxygen-rich liquid stream 209 and nitrogen reflux stream 210.
Nitrogen reflux stream 210 is combined with internal liquid
nitrogen stream 116 from liquefaction heat exchanger 111 to form
combined nitrogen reflux stream 217. Oxygen-rich liquid stream 209
and combined nitrogen reflux stream 2171 are then both introduced
into low-pressure distillation column 211.
[0114] Low-pressure distillation column 211 produces at least cold
waste nitrogen stream 212, and liquid oxygen stream 214.
Medium-pressure distillation column 208 also produces
medium-pressure nitrogen stream 215. Medium-pressure nitrogen
stream 215 is introduced into main heat exchanger 206 and exits as
warm medium-pressure nitrogen stream 216. Cold waste nitrogen
stream 212 is introduced into main heat exchanger 206 and exits as
low-pressure pure nitrogen stream 213
[0115] Turning now to FIG. 3 details of one non-limiting example of
liquefaction heat exchanger 511 (as described below) as known in
the art are illustrated. In the interest of clarity and
consistency, element numbers 507 (low-pressure nitrogen stream),
508 (medium-pressure nitrogen stream), 516 (liquid nitrogen
stream), 519 (inlet natural gas stream), and 520 (liquid natural
gas stream) from FIG. 5 are used.
[0116] Mixed refrigerant cycle 390 includes warm mixed refrigerant
return steam 350, which is at reduced pressure. Mixed refrigerant
return stream 350 has the pressure increased in mixed refrigerant
compressor 351, thereby producing pressurized mixed refrigerant
stream 352. Pressurized mixed refrigerant stream 352 enters mixed
refrigerant cooler 353, thereby producing cooled pressurized mixed
refrigerant stream 354. Cooled pressurized mixed refrigerant stream
354 is introduced to first phase separator vessel 355, which
produces first vapor portion 356 and first liquid portion 357.
First vapor portion 356 and first liquid portion 357 may be
combined to form first combined mixed refrigerant stream 358, which
is introduced into liquefaction heat exchanger 511. Alternatively,
first liquid portion 357 and first vapor portion 356 may be
introduced independently to exchanger 511 and first vapor portion
356 is cooled to a colder temperature than first liquid portion 357
(not shown). In general, it is understood that there are numerous
variations of the mixed refrigerant system which one of ordinary
skill in the art knows to apply in similar cycles.
[0117] After passing through liquefaction heat exchanger 511, first
combined mixed refrigerant stream 358 exits as intermediate mixed
refrigerant stream 359. Intermediate mixed refrigerant stream 359
is reduced in pressure across mixed refrigerant pressure letdown
valve 386 and then is introduced into liquefaction heat exchanger
511 as intermediate mixed refrigerant stream 363. After passing
through liquefaction heat exchanger 511, intermediate mixed
refrigerant stream 363 exits as warm mixed refrigerant return steam
350.
[0118] Nitrogen refrigeration cycle 391 includes receiving
low-pressure nitrogen stream 507 from the air separation unit 506
(not shown in FIG. 3). Low-pressure nitrogen stream 507 is combined
with first nitrogen recycle stream 385, and the pressure of the
combined stream is increased in LP nitrogen compressor 364, thereby
producing warm medium-pressure nitrogen stream 365. Warm
medium-pressure nitrogen stream 365 enters first nitrogen cooler
366, thereby producing cooled medium-pressure nitrogen stream
367.
[0119] Cooled medium-pressure nitrogen stream 367 is combined with
medium-pressure nitrogen stream 508 from the ASU and second
nitrogen recycle stream 384, thereby producing combined
medium-pressure nitrogen stream 368. The pressure of
medium-pressure nitrogen stream 368 is increased in MP nitrogen
compressor 369, thereby producing warm intermediate-pressure
nitrogen stream 370. Warm intermediate-pressure nitrogen stream 370
enters second nitrogen cooler 371, thereby producing cooled
intermediate-pressure nitrogen stream 372.
[0120] Cooled intermediate-pressure nitrogen stream 372 is then
further compressed in HP nitrogen compressor 373, thereby producing
medium-pressure nitrogen stream 374. Medium-pressure nitrogen
stream 374 then passes through liquefaction heat exchanger 511,
after which it is removed at two locations. Typically, first
nitrogen refrigeration stream 375 will be removed as a vapor
stream, and second nitrogen refrigeration stream 378 will be
removed as a liquid stream.
[0121] The first location is via first nitrogen refrigeration
stream 375, which is then introduced into nitrogen expander 376.
Nitrogen expander 376 is connected to HP nitrogen booster 373 by a
common drive shaft. After having the pressure reduced in nitrogen
expander 376, this stream exits as expanded nitrogen stream 377,
which is then introduced into liquefaction heat exchanger 511.
Expanded nitrogen stream 377 exits liquefaction heat exchanger 511
as second nitrogen recycle stream 384.
[0122] The second location is via second nitrogen refrigeration
stream 378. Second nitrogen refrigeration stream 378 passes through
nitrogen refrigeration cycle pressure letdown valve 387 and is then
introduced into third phase separator vessel 379. This produces
nitrogen vapor portion 380 and nitrogen liquid portion 381.
Nitrogen vapor portion 380 and nitrogen liquid portion 381 are
combined to form combined nitrogen stream 382. A portion of
combined nitrogen stream 382 is removed as liquid nitrogen stream
516. The remaining portion of combined nitrogen stream 382 is
introduced into liquefaction heat exchanger 511 as cold nitrogen
recycle stream 383. Cold nitrogen recycle stream 383 exits
liquefaction heat exchanger 511 as first nitrogen recycle stream
385. Mixed refrigerant cycle 390 and nitrogen refrigeration cycle
391 work together to provide sufficient refrigeration duty to
liquefy inlet natural gas stream 519 into liquid natural gas stream
520. In addition, these combined refrigeration streams also provide
sufficient additional refrigeration duty via internal liquid
nitrogen stream 517, to satisfy the duty requirements of air
separation unit 506 (not shown in FIG. 3). A portion 518 of liquid
nitrogen stream 516 may be removed as LIN product (i.e. not sent to
ASU).
[0123] Turning now to FIG. 4, an example of an air separation
system in accordance with the present invention is described. In
the interest of clarity and consistency, element numbers that are
common with FIG. 2 are maintained.
[0124] Inlet air stream 201 is compressed in main air compressor
(MAC) 202, thereby producing compressed inlet air stream 203.
Compressed inlet air stream 203 is then introduced into front end
purification device 204, thereby producing purified inlet air
stream 205. Purified inlet air stream 205 is divided into at least
a first portion 401 and a second portion 402. First portion 401 of
purified inlet air stream then enters main heat exchanger 206.
Inside main heat exchanger 206, first portion 401 of purified inlet
air stream indirectly exchanges heat with a number of streams
(described below) thus producing cold air stream 207. Cold air
stream 207 is then introduced into medium-pressure distillation
column 208.
[0125] Second portion 402 of purified inlet air stream has the
pressure increased in booster air compressor 403, which produces
boosted inlet air stream 404. Boosted inlet air stream 404 is
divided into at least a first portion 405 and a second portion 406.
First portion 405 of boosted inlet air stream then enters main heat
exchanger 206. Inside main heat exchanger 206, first portion 405 of
boosted inlet air stream indirectly exchanges heat with a number of
streams thus producing cold boosted air stream 407. Cold boosted
air stream 407 is then introduced into medium-pressure distillation
column 208.
[0126] Second portion 406 of boosted inlet air stream is then
reduced in pressure in expander 408, which produces expanded second
portion of boosted inlet air stream 409. Expanded second portion of
boosted inlet air stream 409 then enters main heat exchanger 206.
Inside main heat exchanger 206, expanded second portion of boosted
inlet air stream 409 indirectly exchanges heat with a number of
streams thus producing cold expanded second portion of boosted
inlet air stream 410. Cold expanded second portion of boosted inlet
air stream 410 is then introduced into medium-pressure distillation
column 208.
[0127] Medium-pressure distillation column 208 produces at least
oxygen-rich liquid stream 209 and nitrogen reflux stream 210.
Nitrogen reflux stream 210 is combined with internal liquid
nitrogen stream 517 from liquefaction heat exchanger 511 (below),
to form combined nitrogen reflux stream 411. Oxygen-rich liquid
stream 209 and combined nitrogen reflux stream 411 are then both
introduced into low-pressure distillation column 211.
[0128] Low-pressure distillation column 211 produces at least cold
waste nitrogen stream 212, and liquid oxygen stream 214.
Medium-pressure distillation column 208 also produces
medium-pressure nitrogen stream 215. Medium-pressure nitrogen
stream 215 is introduced into main heat exchanger 206 and exits as
warm medium-pressure nitrogen stream 216. Cold waste nitrogen
stream 212 is introduced into main heat exchanger 206 and exits as
low-pressure pure nitrogen stream 213
[0129] Turning now to FIG. 5, a combined ASU and LNG system
according to one embodiment of the present invention is described.
In the interest of clarity and consistency, element numbers that
are common with FIGS. 2 and 4 are maintained.
[0130] Inlet air stream 201 is compressed in main air compressor
(MAC) 202, thereby producing compressed inlet air stream 203.
Compressed inlet air stream 203 is then introduced into front end
purification device 204, thereby producing purified air stream 205.
Purified air stream 205 is divided into first air stream 401 and
second air stream 402. First air stream 401 enters ASU 506. Second
air stream 402 is further compressed in booster air compressor
(BAC) 403, thereby producing boosted air stream 404. Boosted air
stream 404 then enter air separation unit 506.
[0131] Air separation unit 506 produces at least low-pressure pure
nitrogen stream 213, warm medium-pressure nitrogen stream 216, and
liquid oxygen stream 214. Liquid oxygen stream 214 is sent liquid
oxygen storage device 510. In order to produce the desired flowrate
in liquid oxygen stream 214, it is necessary to introduce
additional refrigeration duty, in the form of internal liquid
nitrogen stream 517.
[0132] Low-pressure pure nitrogen stream 213, warm medium-pressure
nitrogen stream 216, and inlet natural gas stream 519 are
introduced into liquefaction heat exchanger 511. Liquefaction heat
exchanger 511 outputs at least liquid natural gas stream 520 and
liquid nitrogen stream 516. A portion of liquid nitrogen stream 516
may be removed as export liquid nitrogen stream 518, and not sent
to the ASU. Liquid natural gas stream 520 is then sent to liquid
natural gas storage device 521.
[0133] The objective of the current system is to optimize, in terms
of operating expense and capital expense, a process for production
of LOX and LNG with a mass flow ratio of LOX/LNG between 2 to 5,
preferably between 3 to 4. As used herein, the mass flow ratio of
LOX/LNG is defined as the mass flowrate of liquid oxygen stream 509
divided by the mass flowrate of liquid natural gas stream 520.
[0134] Ordinarily, ASU process designs (and indeed standard ASUs)
are designed and optimized around a system which utilizes a MAC and
a BAC, or a single high-pressure MAC, to produce primarily
medium-pressure gaseous oxygen GOX with small (or negligible)
amounts of cryogenic liquid (such as LOX, LIN, and/or LAR).
Typically, such a system produces the GOX at a pressure of between
40 and 50 bara.
[0135] However, one aspect of the current invention is to use all
of the available compression energy to produce primarily (or
exclusively) LOX. As described above, the prior art system
indicated in FIG. 1 does not include a BAC. Such systems are indeed
very common. However, the current invention includes a BAC, which
adds additional refrigeration capability. In the present case, the
system is designed such that this additional refrigeration is being
optimized to produce LOX. This optimization and the increased
refrigeration available within the ASU, thus allows for the overall
required refrigeration duty of liquefaction heat exchanger 511 to
be reduced.
[0136] Specifically, in order to provide additional refrigeration
duty to a cycle, additional energy must be added to the cycle. In
this case, the additional energy comes in the form of the energy
required by BAC 403 to increase the pressure in boosted inlet air
stream 404. Then, the basic principle of isentropic expansion,
through expander 408, results in expanded second portion 409.
Expanded second portion 409 will have essentially the same entropy
as boosted inlet air stream 404, but since it will be at a
significantly lower pressure, will be significantly colder, thus
adding significant additional refrigeration duty to the cycle.
[0137] In the present inventive system, this increase in internal
refrigeration duty provided by BAC 403 will add between 10% to 50%,
preferably 20% to 40%, or at least 10%, of the total refrigeration
duty to the ASU cycle to produce liquid products LOX and/or LIN
with preferably no (or very small) gaseous products. This will
reduce the refrigeration required by mixed refrigerant cycle 390
and/or nitrogen refrigeration cycle 391 accordingly.
[0138] In general, the specific power to produce LOX is about 3
times larger than the power to produce only medium-pressure GOX.
Therefore, an optimized MAC/BAC (or single high-pressure MAC) ASU
scheme is only able to provide approximately 1/3.sup.rd of the
refrigeration required to liquefy all of the LOX. The remainder of
the required refrigeration (i.e, approximately 2/3rds) must be
provided by external source (such as imported LIN).
[0139] A second aspect of the current invention is to incorporate a
liquefier process which simultaneously produces the required
balance (approximately 2/3.sup.rd portion) of the LOX refrigeration
demand. The liquefier is designed to produce approximate LIN/LNG
mass flow ratio of between 2 to 5, (preferably 2.5 ) since the
final product demand is LOX/LNG in the mass flow ratio of between 3
to 4 (preferably 3.4). A third aspect of this invention is an
optimized (especially relating to operating expense and capital
expense) process scheme for producing this LIN/LNG mass flow ratio
of 2 to 5, preferably 2 to 3 (more preferably 2.5). As used herein,
the mass flow ratio of LIN/LNG is defined as the mass flowrate of
internal liquid nitrogen stream 517 divided by the mass flowrate of
liquid natural gas stream 520.
[0140] Mixed refrigerant (MR) refrigeration cycles are state-of-art
for producing LNG but are not cold enough (-160 C for MR cycle) to
produce LIN (-190 C). State-of-art LIN production is with N2 cycle
only since the capital expenditure penalty of having both N2+MR
cycles is not compensated by the operating expense efficiency
savings to produce only LIN. However, producing the target LIN/LNG
mass flow ratio of 2.5 yields a significant MR refrigerant (-160 C
level refrigeration) as compared to the N2 cycle (-190 C level
refrigeration) which allows for an optimized heat exchange
profile.
[0141] In other words, a target LIN/LNG=2.5 mass flow ratio yields
an optimized split of the refrigeration load between N2 cycle and
MR cycle where the MR cycle supplements the traditional N2 cycle to
produce LIN. The result is taking state-of the art LNG specific
power (0.27 kW/Nm3) and applying the balance of power to the LIN we
find 0.41 kW/Nm3 LIN which is 20 to 25% less than N2 expansion only
cycle.
EXAMPLE
[0142] The mass flowrate of liquid oxygen stream 509=4300 metric
tons per day
[0143] The mass flowrate of liquid natural gas stream 520=1250
metric tons per day
[0144] The mass flowrate of internal liquid nitrogen stream
517=2000 metric tons per day
[0145] The mass flow ratio of LOX/LNG=4300/1250=3.4
[0146] The mass flow ratio of LIN/LNG=3192/2000=4.2
[0147] The mass flow ratio of LIN to ASU/LOX
produced=3192/4300=0.74
[0148] It will be understood that many additional changes in the
details, materials, steps and arrangement of parts, which have been
herein described in order to explain the nature of the invention,
may be made by those skilled in the art within the principle and
scope of the invention as expressed in the appended claims. Thus,
the present invention is not intended to be limited to the specific
embodiments in the examples given above.
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