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Patent 2867436 Summary

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(12) Patent: (11) CA 2867436
(54) English Title: LNG FORMATION
(54) French Title: FORMATION DE GAZ NATUREL LIQUEFIE (GNL)
Status: Deemed expired
Bibliographic Data
(51) International Patent Classification (IPC):
  • C10L 3/10 (2006.01)
  • F25J 1/02 (2006.01)
(72) Inventors :
  • OELFKE, RUSSELL H. (United States of America)
(73) Owners :
  • EXXONMOBIL UPSTREAM RESEARCH COMPANY (United States of America)
(71) Applicants :
  • EXXONMOBIL UPSTREAM RESEARCH COMPANY (United States of America)
(74) Agent: BORDEN LADNER GERVAIS LLP
(74) Associate agent:
(45) Issued: 2019-04-09
(86) PCT Filing Date: 2013-03-04
(87) Open to Public Inspection: 2013-10-03
Examination requested: 2018-01-18
Availability of licence: N/A
(25) Language of filing: English

Patent Cooperation Treaty (PCT): Yes
(86) PCT Filing Number: PCT/US2013/028906
(87) International Publication Number: WO2013/148075
(85) National Entry: 2014-09-15

(30) Application Priority Data:
Application No. Country/Territory Date
61/618,290 United States of America 2012-03-30
61/695,592 United States of America 2012-08-31

Abstracts

English Abstract

Systems and a method for the formation of a liquefied natural gas (LNG) are disclosed herein. The system includes a refrigeration system configured to chill a natural gas using a refrigerant mixture including a noble gas. The system also includes an autorefrigeration system configured to use the natural g self-refrigerant to form the LNG from the natural gas.


French Abstract

L'invention concerne des systèmes et un procédé pour la formation d'un gaz naturel liquéfié (GNL). Le système comprend un système de réfrigération conçu pour réfrigérer un gaz naturel à l'aide d'un mélange de fluide frigorigène comprenant un gaz noble. Le système comprend également un système d'autoréfrigération configuré pour utiliser l'auto-réfrigérant naturel g pour former le GNL à partir du gaz naturel.

Claims

Note: Claims are shown in the official language in which they were submitted.



34

CLAIMS:

1. A system for formation of a liquefied natural gas (LNG), including:
a refrigeration system configured to chill a natural gas using a refrigerant
mixture
comprising xenon, krypton, or any combination thereof;
a first refrigeration system configured to cool the natural gas using a non-
hydrocarbon
refrigerant, but not the refrigerant mixture, prior to flowing the natural gas
into the
refrigeration system; and
an autorefrigeration system configured to use a chilled natural gas as a self-
refrigerant
to form the LNG from the chilled natural gas.
2. The system of claim 1, including a nitrogen rejection unit upstream of
the
autorefrigeration system.
3. The system of claims 1 or 2, wherein the system is configured to chill
the natural gas
for hydrocarbon dew point control.
4. The system of claims 1 or 2, wherein the system is configured to chill
the natural gas
for natural gas liquid (NGL) extraction.
5. The system of claims 1 or 2, wherein the system is configured to
separate methane
and lighter gases from carbon dioxide and heavier gases.
6. The system of claims 1 or 2, wherein the system is configured to prepare

hydrocarbons for liquefied petroleum gas (LPG) production storage.
7. The system of claims 1 or 2, wherein the system is configured to
condense a reflux
stream.
8. The system of claims 1 or 2, wherein the refrigerant mixture comprises
xenon,
krypton, argon, nitrogen, or a combination thereof.


35

9. The system of claims 1 or 2, wherein the refrigeration system comprises
a mechanical
refrigeration system, valve expansion system, turbine expansion system, or a
combination
thereof.
10. The system of claims 1 or 2, wherein the refrigerant mixture includes a
hydrocarbon,
and wherein the hydrocarbon comprises methane, ethane, propane, butane, or a
combination
thereof.
11. The system of claims 1 or 2, wherein the refrigeration system includes
multiple
cooling cycles.
12. The system of claims 1 or 2, wherein the refrigeration system includes
multiple
cooling cycles, including:
one or more pre-cooling stages, wherein the refrigerant mixture includes a
noble gas,
nitrogen, a hydrocarbon, or any combinations thereof, and
one or more deep cooling cycles, wherein the refrigerant mixture includes a
noble
gas, nitrogen, a hydrocarbon, or any combinations thereof.
13. The system of claims 1 or 2, wherein the refrigerant mixture including
xenon or
krypton is utilized in one or more cooling stages to achieve deeper cooling
than provided by
hydrocarbon refrigerants.
14. The system of claims 1 or 2, including a nitrogen rejection unit,
wherein a liquid feed
from the bottom of the nitrogen rejection unit is used to provide cooling to a
reflux condenser
at the top of the nitrogen rejection unit.
15. The system of claims 1 or 2, wherein the refrigerant mixture comprises
a pure
component refrigerant.
16. A method for formation of a liquefied natural gas (LNG), including:
chilling a natural gas in a refrigeration system, wherein the refrigeration
system uses
a refrigerant mixture comprising xenon, krypton, or a combination thereof;


36

cooling the natural gas in a first refrigeration system prior to chilling the
natural gas
in the refrigeration system, wherein the first refrigeration system uses a non-
hydrocarbon
refrigerant but not the refrigerant mixture; and
liquefying the chilled natural gas to form the LNG in an autorefrigeration
system.
17. The method of claim 16, wherein chilling the natural gas in the
refrigeration system
includes:
compressing the refrigerant mixture to provide a compressed refrigerant
mixture;
optionally cooling the compressed refrigerant mixture by indirect heat
exchange with
a cooling fluid;
expanding the compressed refrigerant mixture to cool the compressed
refrigerant
mixture, thereby producing an expanded, cooled refrigerant mixture;
passing said expanded, cooled refrigerant mixture to a first heat exchange
area;
optionally compressing the natural gas;
optionally cooling said the natural gas by indirect heat exchange with an
external
cooling fluid; and
heat exchanging the natural gas with the expanded, cooled refrigerant mixture.
18. The method of claims 16 or 17, wherein the refrigerant mixture
comprises nitrogen,
a hydrocarbon, or a combination thereof.
19. The method of claims 16 or 17, including liquefying the natural gas to
form the LNG
via a number of expansion valves or hydraulic expansion turbines and flash
drums.
20. The method of claims 16 or 17, including:
chilling the natural gas via one or more pre-cooling steps using a first
refrigerant
mixture, wherein the first refrigerant mixture comprises a noble gas,
nitrogen, a hydrocarbon,
or a combination thereof, and
chilling the natural gas via one or more deep cooling steps using a second
refrigerant
mixture, wherein the second refrigerant mixture comprises a noble gas,
nitrogen, a
hydrocarbon, or a combination thereof.


37

21. The method of claims 16 or 17, including using the refrigerant mixture
including
xenon or krypton in one or more cooling stages to achieve deeper cooling than
provided by
hydrocarbon refrigerants.
22. A cascade cooling system for formation of a liquefied natural gas
(LNG), including:
a first refrigeration system configured to cool the natural gas using a non-
hydrocarbon
refrigerant, wherein the first refrigeration system includes a number of first
chillers
configured to allow for cooling of the natural gas via an indirect exchange of
heat between
the natural gas and the non-hydrocarbon refrigerant;
a second refrigeration system configured to chill the cooled natural gas using
a
refrigerant mixture comprising xenon, krypton, or a combination thereof,
wherein the second
refrigeration system includes a number of second chillers configured to allow
for cooling of
the natural gas via an indirect exchange of heat between the natural gas and
the refrigerant
mixture, wherein the first refrigerant system does not use the refrigerant
mixture for cooling
of the natural gas; and
an autorefrigeration system configured to form the LNG from the chilled
natural gas,
wherein the autorefrigeration system includes a number of expansion valves,
hydraulic
expansion turbines, or any combination thereof, and flash drums.
23. The cascade cooling system of claim 22, wherein the first refrigeration
system
includes a compressor that is configured to compress the non-hydrocarbon
refrigerant and a
condenser that is configured to cool the non-hydrocarbon refrigerant.
24. The cascade cooling system of claims 22 or 23, wherein the second
refrigeration
system includes a compressor that is configured to compress the refrigerant
mixture and a
condenser that is configured to cool the refrigerant mixture.
25. The cascade cooling system of claims 22 or 23, wherein the number of
first chillers
include evaporators configured to cool the natural gas by at least partially
vaporizing the
non-hydrocarbon refrigerant via a transfer of heat from the natural gas to the
non-hydrocarbon
refrigerant.


38

26. The cascade cooling system of claims 22 or 23, wherein the number of
second chillers
include evaporators configured to chill the cooled natural gas by vaporizing
the refrigerant
mixture via a transfer of heat from the natural gas to the refrigerant
mixture.
27. The cascade cooling system of claims 22 or 23, wherein the LNG includes
a liquid
fraction and a residual vapor fraction, and wherein the cascade cooling system
includes a
liquid separation vessel configured to separate the residual vapor fraction
from the liquid
fraction.
28. The cascade cooling system of claims 22 or 23, including a nitrogen
rejection unit
upstream of the autorefrigeration system.
29. The cascade cooling system of claims 22 or 23, wherein the refrigerant
mixture
comprises a pure component refrigerant.

Description

Note: Descriptions are shown in the official language in which they were submitted.


LNG FORMATION
[0001]
FIELD OF THE INVENTION
100021 The present techniques relate generally to the field of
hydrocarbon recovery and
treatment processes and, more particularly, to systems and methods that form
liquefied
natural gas (LNG) via a refrigeration process. Specifically, provided are
systems and
methods for forming LNG from natural gas using refrigerants that include one
or more noble
gases.
BACKGROUND
[0003] This section is intended to introduce various aspects of the art,
which may be
associated with exemplary embodiments of the present techniques. This
discussion is
believed to assist in providing a framework to facilitate a better
understanding of particular
aspects of the present techniques. Accordingly, it should be understood that
this section
should be read in this light, and not necessarily as admissions of prior art.
[0004] Many low temperature refrigeration systems that are used for
natural gas
processing and liquefaction rely on the use of refrigerants including
hydrocarbon components
and nitrogen to provide external refrigeration. Such hydrocarbon components
may include
methane, ethane, ethylene, propane, and the like. However, the use of
refrigerants including
hydrocarbon components and nitrogen may not be very efficient, since a large
heat transfer
area may be required to provide proper refrigeration of the natural gas. In
addition, the
flammability of the hydrocarbon components within the refrigerants may
increase the risks
associated with the refrigeration process.
[0005] Low temperature refrigeration systems that are used for natural gas
processing
and liquefaction often use synthetic refrigerants, such as R-404A or R-410A,
as substitutes
for the refrigerants including the hydrocarbon components and the nitrogen.
However, such
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synthetic refrigerants are only suitable for levels of refrigeration that are
above around -100
F. In some instances, lower levels of refrigeration may be desirable.
100061 International Patent Application Publication WO/2005/072404, by
Flynn, et al.,
describes a cooling system that includes a first refrigerant cycle including a
first refrigerant
and a second refrigerant cycle including a second refrigerant that is a
mixture of cryogenic
components. The disclosure is also directed to a cooling system that includes
a first
refrigerant cycle including a first refrigerant and a second refrigerant cycle
including a
second refrigerant that is a non-reactive component. The second refrigerant is
free of
fluorocarbons, chlorofluorocarbons, and hydrocarbons. At least a portion of
the second
refrigerant is condensed in the second refrigerant cycle. However, the
disclosure is not
directed to a cooling system that includes any type of autorefrigeration
cycle.
100071 Related information may be found in U.S. Patent Nos. 4,533,372,
4,923,493,
5,265,428, 5,062,270, 5,120,338, 6,053,007, and 5,956,971; U.S. Patent
Application
Publication Nos. 2002/0088249, 2003/0177785, 2007/0193303, 2007/0227185,
2008/0034789, 2008/0087041, 2009/0217701, 2009/0266107, 2010/0018248 ,
2010/0107684, 2010/0186445, 2012/0031144, 2012/0079852, and 2012/0125043; and
International Patent Publication No. WO/2012/015554. Other potentially related
information
may be found in International Patent Publication No. W02007/021351; Foglietta,
J. H., et al.,
"Consider Dual Independent Expander Refrigeration for LNG Production New
Methodology
May Enable Reducing Cost to Produce Stranded Gas," Hydrocarbon Processing,
Gulf
Publishing Co., vol. 83, no. 1, pp. 39-44 (January 2004); U.S. Patent
Application Publication
No. US2003/089125; U.S. Patent No. 6,412,302; U.S. Patent No. 3,162,519; U.S.
Patent No.
3,323,315; German Patent No. DE19517116, and J.M. Campbell, "Gas Conditioning
and
Processing, Vol. 2: The Equipment Modules", 8th edition, John M. Campbell &
Company,
2001.
SUMMARY
100081 An embodiment provides a system for the formation of a liquefied
natural gas
(LNG). The system includes a refrigeration system configured to chill a
natural gas using a
refrigerant mixture including a noble gas. The system also includes an
autorefrigeration
system configured to use the natural gas as a self-refrigerant to form the LNG
from the
natural gas.

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10009] Another embodiment provides a method for the formation of LNG. The
method
includes chilling a natural gas in a refrigeration system, wherein the
refrigeration system uses
a refrigerant mixture includes a noble gas. The method also includes
liquefying the natural
gas to form the LNG in an autorefrigeration system.
PI 0] Another embodiment provides a cascade cooling system for formation of
LNG.
The cascade cooling system includes a first refrigeration system configured to
cool the
natural gas using a non-hydrocarbon refrigerant, wherein the first
refrigeration system
includes a number of first chillers configured to allow for cooling of the
natural gas via an
indirect exchange of heat between the natural gas and the non-hydrocarbon
refrigerant. The
cascade cooling system also includes a second refrigeration system configured
to chill the
natural gas using a refrigerant mixture including a noble gas, wherein the
second refrigeration
system includes a number of second chillers configured to allow for cooling of
the natural gas
via an indirect exchange of heat between the natural gas and the refrigerant
mixture. The
cascade cooling system further includes an autorefrigeration system configured
to form the
LNG from the natural gas, wherein the autorefrigeration system includes a
number of
expansion valves or hydraulic expansion turbines, or any combination thereof,
and flash
drums.
BRIEF DESCRIPTION OF THE DRAWINGS
PH] The advantages of the present techniques are better understood by
referring to the
following detailed description and the attached drawings, in which:
100121 Fig. 1 is a process flow diagram of a single stage refrigeration
system;
10013] Fig. 2 is a process flow diagram of a two stage refrigeration
system including an
economizer;
10014j Fig. 3 is a process flow diagram of a single stage refrigeration
system including a
heat exchanger economizer;
100151 Fig. 4 is a process flow diagram of a cascade cooling system
including a first
refrigeration system and a second refrigeration system;
10016] Fig. 5 is process flow diagram of an expansion refrigeration
system for
hydrocarbon dew point control;
10017] Fig. 6 is a process flow diagram of an expansion refrigeration
system for NGL
extraction;

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100181 Fig. 7 is a process flow diagram of an LNG production system;
1001[9] Fig. 8 is a simplified process flow diagram of a cascade cooling
system;
10020] Figs. 9A-B are a more detailed process flow diagram of a cascade
cooling system;
100211 Fig. 10 is a more detailed process flow diagram of an
autorefrigeration system;
10022i Fig. 11 is a schematic of a methane pressure-enthalpy (P-H) diagram;
and
10023] Fig. 12 is a process flow diagram of a method for the formation of
LNG.
DETAILED DESCRIPTION OF THE DRAWINGS
100241 In the following detailed description section, specific
embodiments of the present
techniques are described. However, to the extent that the following
description is specific to
a particular embodiment or a particular use of the present techniques, this is
intended to be
for exemplary purposes only and simply provides a description of the exemplary

embodiments. Accordingly, the techniques are not limited to the specific
embodiments
described below, but rather, include all alternatives, modifications, and
equivalents falling
within the spirit and scope of the appended claims.
10025] At the outset, for ease of reference, certain terms used in this
application and their
meanings as used in this context are set forth. To the extent a term used
herein is not defined
below, it should be given the broadest definition persons in the pertinent art
have given that
term as reflected in at least one printed publication or issued patent.
Further, the present
techniques are not limited by the usage of the terms shown below, as all
equivalents,
synonyms, new developments, and terms or techniques that serve the same or a
similar
purpose are considered to be within the scope of the present claims.
100261 "Acid gases" are contaminants that are often encountered in
natural gas streams.
Typically, these gases include carbon dioxide (CO2) and hydrogen sulfide
(1125), although
any number of other contaminants may also form acids. Acid gases are commonly
removed
by contacting the gas stream with an absorbent, such as an amine, which may
react with the
acid gas. When the absorbent becomes acid-gas "rich," a desorption step can be
used to
separate the acid gases from the absorbent. The "lean" absorbent is then
typically recycled
for further absorption. As used herein a "liquid acid gas stream" is a stream
of acid gases that
are condensed into the liquid phase, for example, including CO? dissolved in
H2S and vice-
versa.

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100271 As used herein, "autorefrigeration" refers to a process whereby a
fluid is cooled
via a reduction in pressure. In the case of liquids, autorefrigeration refers
to the cooling of
the liquid by evaporation, which corresponds to a reduction in pressure. More
specifically, a
portion of the liquid is flashed into vapor as it undergoes a reduction in
pressure while
5 passing through a throttling device. As a result, both the vapor and the
residual liquid are
cooled to the saturation temperature of the liquid at the reduced pressure.
For example,
according to embodiments described herein, autorefrigeration of a natural gas
may be
performed by maintaining the natural gas at its boiling point so that the
natural gas is cooled
as heat is lost during boil off. This process may also be referred to as a
"flash evaporation."
[0028] As used herein, a "cascade cycle" refers to a system with two or
more refrigerants,
where a cold second refrigerant is condensed by a warmer first refrigerant.
Thus, low
temperatures may be "cascaded" down from one refrigerant to another. Each
refrigerant in a
cascade may have multiple levels of chilling based on staged evaporating
pressures within
economizers. Cascade cycles are considered to be beneficial for the production
of LNG as
compared to single refrigerant systems, since lower temperatures may be
achieved within
cascade cycles than single refrigerant systems.
100291 A "closed-loop refrigeration cycle" refers to a refrigeration
cycle wherein
substantially no refrigerant enters or exits the cycle during normal
operation.
10030l A "closed-loop refrigeration system" refers to a refrigeration
system comprising
compression, heat exchange, and pressure reduction means in which a
refrigerant is
recirculated without continuous deliberate refrigerant withdrawal. A small
amount of
refrigerant makeup typically is required because of small leakage losses from
the system.
0031] A "compressor" or "refrigerant compressor" includes any unit,
device, or
apparatus able to increase the pressure of a refrigerant stream. This includes
refrigerant
compressors having a single compression process or step, or refrigerant
compressors having
multi-stage compressions or steps, more particularly multi-stage refrigerant
compressors
within a single casing or shell. Evaporated refrigerant streams to be
compressed can be
provided to a refrigerant compressor at different pressures. Some stages or
steps of a
hydrocarbon cooling process may involve two or more refrigerant compressors in
parallel,
series, or both. The present invention is not limited by the type or
arrangement or layout of
the refrigerant compressor or refrigerant compressors, particularly in any
refrigerant circuit.

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10032] A "Controlled-Freeze-Zone" (CFZ) process is a process that has
been proposed to
take advantage of the freezing potential of carbon dioxide in cryogenic
distillation, rather
than avoiding solid carbon dioxide. In the CFZ process, acid gas components
arc separated
by cryogenic distillation through the controlled freezing and melting of
carbon dioxide in a
single column, without the use of freeze-suppression additives. The CFZ
process uses a
cryogenic distillation column with a special internal section, e.g., CFZ
section, to handle the
solidification and melting of carbon dioxide. This CFZ section does not
contain packing or
trays like conventional distillation columns. Instead, the CFZ section
contains one or more
spray nozzles and a melting tray. Solid carbon dioxide forms in the vapor
space in the
distillation column and falls into the liquid on the melting tray.
Substantially all of the solids
that form are confined to the CFZ section. The portions of the distillation
column above and
below the CFZ section of the column are similar to conventional cryogenic
demethanizer
columns. A more detailed description of the CFZ process is disclosed in U. S.
Patent Nos.
4,533,372; 4,923,493; 5,120,338; and 5,265,428.
10033j As used herein, "cooling" broadly refers to lowering and/or dropping
a
temperature and/or internal energy of a substance, such as by any suitable
amount. Cooling
may include a temperature drop of at least about 1 degree Celsius, at least
about 5 degrees
Celsius, at least about 10 degrees Celsius, at least about 15 degrees Celsius,
at least about 25
degrees Celsius, at least about 50 degrees Celsius, at least about 100 degrees
Celsius, and/or
the like. The cooling may use any suitable heat sink, such as steam
generation, hot water
heating, cooling water, air, refrigerant, other process streams (integration),
and combinations
thereof One or more sources of cooling may be combined and/or cascaded to
reach a desired
outlet temperature. The cooling step may use a cooling unit with any suitable
device and/or
equipment. According to one embodiment, cooling may include indirect heat
exchange, such
as with one or more heat exchangers. Heat exchangers may include any suitable
design, such
as shell and tube, plate and frame, counter current, concurrent, extended
surface, and/or the
like. In the alternative, the cooling may use evaporative (heat of
vaporization) cooling and/or
direct heat exchange, such as a liquid sprayed directly into a process stream.
10034] "Cryogenic temperature" refers to a temperature that is about ¨50
C or below.
1N351 As used herein, the terms "deethanizer" and "demethanizer" refer to
distillation
columns or towers that may be used to separate components within a natural gas
stream. For
example, a demethanizer is used to separate methane and other volatile
components from

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ethane and heavier components. The methane fraction is typically recovered as
purified gas
that contains small amounts of inert gases such as nitrogen, CO,, or the like.
100361 The term "gas" is used interchangeably with "vapor," and is
defined as a
substance or mixture of substances in the gaseous state as distinguished from
the liquid or
solid state. Likewise, the term "liquid" means a substance or mixture of
substances in the
liquid state as distinguished from the gas or solid state.
10037! A "heat exchanger" broadly means any device capable of
transferring heat from
one media to another media, including particularly any structure, e.g., device
commonly
referred to as a heat exchanger. Heat exchangers include "direct heat
exchangers" and
"indirect heat exchangers." Thus, a heat exchanger may be a plate-and-frame,
shell-and-tube,
spiral, hairpin, core, core-and-kettle, double-pipe or any other type of known
heat exchanger.
"Heat exchanger" may also refer to any column, tower, unit or other
arrangement adapted to
allow the passage of one or more streams therethrough, and to affect direct or
indirect heat
exchange between one or more lines of refrigerant, and one or more feed
streams.
00381 A "hydrocarbon" is an organic compound that primarily includes the
elements
hydrogen and carbon, although nitrogen, sulfur, oxygen, metals, or any number
of other
elements may be present in small amounts. As used herein, hydrocarbons
generally refer to
components found in natural gas, oil, or chemical processing facilities.
100391 "Hydrofluorocarbons" or HFCs are molecules including H, F, and C
atoms.
Hydrofluorocarbons have H-C and F-C bonds and, depending on the number of
carbon atoms
in the species, C-C bonds. Some examples of hydrofluorocarbons include
fluoroform
(CHF3), pentafluoroethane (C2HF5), tetrafluoroethane (C2H7F4),
heptafluoropropane (C3HF7),
hexafluoropropane (C3H2F6), pentafluoropropane (C3H3F5), and
tetrafluoropropane (C3H4F4),
among other compounds of similar chemical structure.
100401 "Liquefied natural gas" or "LNG" is natural gas generally known to
include a high
percentage of methane. However, LNG may also include trace amounts of other
compounds.
The other elements or compounds may include, but are not limited to, ethane,
propane,
butane, carbon dioxide, nitrogen, helium, hydrogen sulfide, or combinations
thereof, that
have been processed to remove one or more components (for instance, helium) or
impurities
(for instance, water and/or heavy hydrocarbons) and then condensed into a
liquid at almost
atmospheric pressure by cooling.

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100411 "Mixed refrigerant processes" may include, but are not limited to,
a single
refrigeration system using a mixed refrigerant, i.e., a refrigerant with more
than one chemical
componcnt, a hydrocarbon pre-cooled mixed refrigerant system, and a dual mixed
refrigerant
system. In general, mixed refrigerants can include hydrocarbon and/or non-
hydrocarbon
components. Examples of suitable hydrocarbon components typically employed in
mixed
refrigerants can include, but are not limited to, methane, ethane, ethylene,
propane,
propylene, as well as butane and butylene isomers. Non-hydrocarbon components
generally
employed in mixed refrigerants can include carbon dioxide and nitrogen. Mixed
refrigerant
processes employ at least one mixed component refrigerant, but can
additionally employ one
.. or more pure-component refrigerants as well.
10042] "Natural gas" refers to a multi-component gas obtained from a
crude oil well or
from a subterranean gas-bearing formation. The composition and pressure of
natural gas can
vary significantly. A typical natural gas stream contains methane (CH4) as a
major
component, i.e., greater than 50 mol % of the natural gas stream is methane.
The natural gas
stream can also contain ethane (C21-16), higher molecular weight hydrocarbons
(e.g., C3-C20
hydrocarbons), one or more acid gases (e.g., carbon dioxide or hydrogen
sulfide), or any
combinations thereof. The natural gas can also contain minor amounts of
contaminants such
as water, nitrogen, iron sulfide, wax, crude oil, or any combinations thereof.
The natural gas
stream may be substantially purified prior to use in embodiments, so as to
remove
.. compounds that may act as poisons.
10043] As used herein, "natural gas liquids" (NGL) refer to mixtures of
hydrocarbons
whose components are, for example, typically heavier than ethane. Some
examples of
hydrocarbon components of NGL streams include propane, butane, and pentane
isomers,
benzene, toluene, and other aromatic compounds.
1004.11 "Noble gas" refers to any of the chemical elements belonging to
group 18 of the
periodic table. More specifically, the noble gases include helium (He), neon
(Me), argon
(Ar), krypton (Kr), xenon (Xe), and radon (Rn). The noble gases are
characterized by very
low chemical reactivity.
10045] An "open-loop refrigeration cycle" refers to a refrigeration cycle
wherein at least a
.. portion of the refrigerant employed during normal operation originates from
the fluid being
cooled by the refrigeration cycle.

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10046] An "open-loop refrigeration system" is a refrigeration system
comprising
compression, heat exchange, and pressure reduction means in which a
refrigerant is
recirculated, a portion of the refrigerant is continuously withdrawn from the
recirculation
loop, and additional refrigerant is continuously introduced into the
recirculation loop.
10047] A "refrigerant component," in a refrigeration system, will absorb
heat at a lower
temperature and pressure through evaporation and will reject heat at a higher
temperature and
pressure through condensation. Illustrative refrigerant components may
include, but are not
limited to, alkanes, alkenes, and alkynes having one to five carbon atoms,
nitrogen,
chlorinated hydrocarbons, fluorinated hydrocarbons, other halogenated
hydrocarbons, noble
gases, and mixtures or combinations thereof.
100481 "Substantial" when used in reference to a quantity or amount of a
material, or a
specific characteristic thereof, refers to an amount that is sufficient to
provide an effect that
the material or characteristic was intended to provide. The exact degree of
deviation
allowable may depend, in some cases, on the specific context.
Overview
10049] Embodiments described herein provide a hydrocarbon processing
system and
method. Such a hydrocarbon processing system may include or utilize a
refrigeration system,
such as a cascade cooling system. Further, according to embodiments described
herein, the
refrigeration system utilizes a refrigerant mixture including a noble gas.
[0050] Hydrocarbon processing systems include the conventional systems
known to those
skilled in the art. Hydrocarbon production and treatment processes include,
but are not
limited to, chilling natural gas for NGL extraction, chilling natural gas for
hydrocarbon dew
point control, chilling natural gas for CO2 removal, liquefied petroleum gas
(LPG) production
storage, condensation of reflux in deethanizers/demethanizers, and natural gas
liquefaction to
produce LNG.
10051] Although many refrigeration cycles have been used to process
hydrocarbons, one
cycle that is used in LNG liquefaction plants is the cascade cycle, which uses
multiple single
component refrigerants in heat exchangers arranged progressively to reduce the
temperature
of the gas to a liquefaction temperature. Another cycle that is used in LNG
liquefactions
plants is the multi-component refrigeration cycle, which uses a multi-
component refrigerant
in specially designed exchangers. In addition, another cycle that is used in
LNG liquefaction
plants is the expander cycle, which expands gas from feed gas pressure to a
low pressure with

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a corresponding reduction in temperature. Natural gas liquefaction cycles may
also use
variations or combinations of these three cycles.
100521 LNG is prepared from a feed gas by refrigeration and liquefaction
technologies.
Optional steps include condensate removal, CO2 removal, dehydration, mercury
removal,
5 nitrogen stripping, H2S removal, and the like. After liquefaction, LNG
may be stored or fed
to a gas pipeline for sale or use. Conventional liquefaction processes can
include: APCI
Propane pre-cooled mixed refrigerant; C3MR; DUAL MR; Phillips Optimized
Cascade;
Prico single mixed refrigerant; TEAL dual pressure mixed refrigerant;
Linde/Statoil multi
fluid cascade; Axens dual mixed refrigerant, DMR; and the Shell processes C3MR
and DMR.
10 [00531 Carbon dioxide removal, i.e., separation of methane and
lighter gases from CO?
and heavier gases, may be achieved with cryogenic processes, such as the
Controlled Freeze
Zone technology available from ExxonMobil Corporation.
100541 While the method and systems described herein are discussed with
respect to the
formation of LNG from natural gas, the method and systems may also be used for
a variety of
other purposes. For example, the method and systems described herein may be
used to chill
natural gas for hydrocarbon dew point control, perform natural gas liquid
(NGL) extraction,
separate methane and lighter gases from carbon dioxide and heavier gases,
prepare
hydrocarbons for LPG production, or condense a reflux stream in deethanizeis
and/or
demethanizers, among others.
Refrigerants
100551 The refrigerants that are utilized according to embodiments
described herein may
be one or more single component refrigerants, or refrigerant mixtures
including multiple
components. Refrigerants may include methane, ethane, ethylene, propane,
butane, and
nitrogen, or combinations thereof. In embodiments described herein,
refrigerants in one or
more refrigeration stages use non-flammable materials that include noble gases
and mixtures
of noble gases. Refrigerants may be imported and stored on-site or,
alternatively, some of the
components of the refrigerant may be prepared on-site, typically by a
distillation process
integrated with the hydrocarbon processing system. Exemplary mixed
refrigerants are
disclosed in U.S. Patent No. 6,530,240.
10056] Commercially available refrigerants including fluorocarbons (FCs) or
hydrofluorocarbons (HFCs) are used in various applications, as are
refrigerants including
ammonia, sulfur dioxide, or halogenated hydrocarbons. Exemplary refrigerants
are

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11
commercially available from DuPont Corporation, including the ISCEONIT family
of
refrigerants, the SUVA family of refrigerants, the OPTEONO family of
refrigerants, and
the FREON family of refrigerants.
10057] Multicomponent refrigerants are commercially available. For
example, R-401A is
a HCFC blend of R-32, R-152a, and R-124. R-404A is a HFC blend of 52 wt.% R-
143a, 44
wt.% R-125, and 4 wt.% R-134a. R-406A is a blend of 55 wt.% R-22, 4 wt.% R-
600a, and
41 wt.% R-142b. R-407A is a HFC blend of 20 wt.% R-32, 40 wt.% R-125, and 40
wt.% R-
134a. R-407C is a hydrofluorocarbon blend of R-32, R-125, and R-134a. R-408A
is a HCFC
blend of R-22, R-125, and R-143a. R-409A is a HCFC blend of R-22, R-124, and R-
142b.
R-410A is a blend of R-32 and R-125. R-500 is a blend of 73.8 wt.% R-12 and
26.2 wt.% of
R-152a. R-502 is a blend of R-22 and R-115.
[0058] In embodiments discussed herein, refrigerants in one or more
refrigeration stages
may also include a noble gas or a noble gas mixture. The six naturally
occurring noble gases
are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon
(Rn). A noble
gas can be used alone or in combination with other noble gases, or in
combination with other
refrigerant components. In some embodiments, the noble gas used as a
refrigerant is xenon,
krypton, argon, or combinations thereof.
100591 Because noble gases are non-flammable, they reduce the risk of
handling
refrigerants. In addition, because noble gases exist in the atmosphere and are
readily
collected, any noble gas refrigerant that escapes the refrigeration system can
be recycled.
Further, if released into the environment, noble gases do not have any ozone
depleting
potential or greenhouse warming potential.
10060] Noble gas refrigerants may provide cooling below about -50 F, or
below about -
100 F, or below about -120 F, or from about -50 F to about -162 F, or from
about -50 F to
about -244 F, or from about -50 F to about -303 F. In multistage
refrigeration systems,
noble gas refrigerants may be utilized in later stages to achieve deeper
cooling than provided
by hydrocarbon refrigerants, such as below about -50 F, or below about -100
F, or below
about -120 F, or from about -50 F to about -162 F, or from about -90 F to
about -162 F, or
from about -100 F to about -162 F, or from about -120 F to about -162 F,
or from about -
50 F to about -244 F, or from about -90 F to about -244 F, or from about -
100 F to about -
244 F, or from about -120 F to about -244 F, or from about -50 F to about -
303 F, or from
about -90 F to about -303 F, or from about -100 F to about -303 F, or from
about -120 F
to about -303 F.

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100611 In various embodiments, any of a number of different types of
hydrocarbon
processing systems can be used with any of the refrigeration systems described
herein. In
addition, the refrigeration systems described herein may utilize any of the
refrigerants
described above.
Refrigeration Systems
100624 Hydrocarbon systems and methods often include refrigeration
systems that utilize
mechanical refrigeration, valve expansion, turbine expansion, or the like.
Mechanical
refrigeration typically includes compression systems and absorption systems,
such as
ammonia absorption systems. Compression systems are used in the gas processing
industry
for a variety of processes. For example, compression systems may be used for
chilling
natural gas for NGL extraction, chilling natural gas for hydrocarbon dew point
control, LPG
production storage, condensation of reflux in deethanizers or demethanizers,
natural gas
liquefaction to produce LNG, or the like. Further, other commercial processes
that utilize
refrigeration may take advantage of the decreased flammability inherent in the
noble gases to
replace other refrigerants, such as ammonia.
100631 Fig. 1 is a process flow diagram of a single stage refrigeration
system 100. In
various embodiments, the single stage refrigeration system 100 utilizes a
refrigerant mixture
including a noble gas. The single stage refrigeration system 100 includes an
expansion valve
102, a chiller 104, a compressor 106, a condenser 108, and an accumulator 110.
A saturated
liquid refrigerant 112 may flow from the accumulator 110 to the expansion
valve 102, and
may expand across the expansion valve 102 isenthalpically. On expansion, some
vaporization occurs, creating a chilled refrigerant mixture 114 that includes
both vapor and
liquid. The refrigerant mixture 114 may enter the chiller 104, also known as
the evaporator,
at a temperature lower than the temperature to which a process stream 116,
such as a natural
gas, is to be cooled. The process stream 116 flows through the chiller 104 and
exchanges
heat with the refrigerant mixture 114. As the process stream 116 exchanges
heat with the
refrigerant mixture 114, the process stream 116 is cooled, while the
refrigerant mixture 114
may at least partially vaporize, creating a saturated vapor refrigerant 118.
10064] After leaving the chiller 104, the saturated vapor refrigerant
118, as well as any
remaining liquid refrigerant, is compressed within the compressor 106, and is
then flowed
into the condenser 108. Within the condenser 108, the saturated vapor
refrigerant 118 is
converted to a saturated, or slightly sub-cooled, liquid refrigerant 120. The
liquid refrigerant
120 may then be flowed from the condenser 108 to the accumulator 110. The
accumulator

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110, which is also known as a surge tank or receiver, may serve as a reservoir
for the liquid
refrigerant 120. The liquid refrigerant 120 may be stored within the
accumulator 110 before
being expanded across the expansion valve 102 as the saturated liquid
refrigerant 112.
[0065] It is to be understood that the process flow diagram of Fig. 1 is
not intended to
indicate that the single stage refrigeration system 100 is to include all the
components shown
in Fig. 1. Further, the single stage refrigeration system 100 may include any
number of
additional components not shown in Fig. 1, depending on the details of the
specific
implementation. For example, in some embodiments, a refrigeration system can
include two
or more compression stages. In addition, the refrigeration system 100 may
include an
economizer, as discussed further with respect to Fig. 2.
[00661 Fig. 2 is a process flow diagram of a two stage refrigeration
system 200 including
an economizer 202. Like numbered items are as described with respect to Fig.
1. The
economizer 202 may be any device or process modification that decreases the
compressor
power usage for a given chiller duty. Conventional economizers 202 include,
for example,
flash tanks and heat exchange economizers.
[00671 As shown in Fig. 2, the saturated liquid refrigerant 112 leaving
the accumulator
110 may be expanded across the expansion valve 102 to an intermediate pressure
at which
vapor and liquid may be separated. The expansion valve 102 may be used to
control the
downstream temperature and pressure of the saturated liquid refrigerant 112.
For example, as
the saturated liquid refrigerant 112 flashes across the expansion valve 102, a
vapor refrigerant
204 and liquid refrigerant 206 are produced at a lower pressure and
temperature than the
saturated liquid refrigerant 112. The vapor refrigerant 204 and the liquid
refrigerant 206 may
then be flowed into the economizer 202. In various embodiments, the economizer
202 is a
flash tank that effects the separation of the vapor refrigerant 204 and the
liquid refrigerant
206. The vapor refrigerant 204 may be flowed to an intermediate pressure
compressor stage,
at which the vapor refrigerant 204 may be combined with saturated vapor
refrigerant 118
exiting a first compressor 210, creating a mixed saturated vapor refrigerant
208. The mixed
saturated vapor refrigerant 208 may then be flowed into a second compressor
212.
10068] From the economizer 202, the liquid refrigerant 206 may be
isenthalpically
expanded across a second expansion valve 214. On expansion, some vaporization
may occur,
creating a refrigerant mixture 216 that includes both vapor and liquid,
lowering the
temperature and pressure. The refrigerant mixture 216 may have a higher liquid
content than

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14
refrigerant mixtures in systems without economizers. The higher liquid content
may reduce
the refrigerant circulation rate and/or reduce the power usage of the first
compressor 210.
100691 The refrigerant mixture 216 enters the chiller 104, also known as
the evaporator,
at a temperature lower than the temperature to which the process stream 116 is
to be cooled.
The process stream 116 is cooled within the chiller 104, as discussed above
with respect to
Fig. 1. In addition, the saturated vapor refrigerant 118 is flowed through the
compressors 210
and 212 and the condenser 108, and the resulting liquid refrigerant 120 is
stored within the
accumulator 110, as discussed above with respect to Fig. 1.
100701 It is to be understood that the process flow diagram of Fig. 2 is
not intended to
indicate that the two stage refrigeration system 200 is to include all the
components shown in
Fig. 2. Further, the two stage refrigeration system 200 may include any number
of additional
components not shown in Fig. 2, depending on the details of the specific
implementation.
For example, the two stage refrigeration system 200 may include any number of
additional
economizers or other types of equipment not shown in Fig. 2. In addition, the
economizer
202 may be a heat exchange economizer rather than a flash tank. The heat
exchange
economizer may also be used to decrease refrigeration circulation rate and
reduce compressor
power usage.
100711 In some embodiments, the two stage refrigeration system 200
includes more than
one economizer 202, as well as more than two compressors 210 and 212. For
example, the
two stage refrigeration system 200 may include two economizers and three
compressors. In
general, if the refrigeration system 200 includes X number of economizers, the
refrigeration
system 200 will include X +1 number of compressors. Such a refrigeration
system 200 with
multiple economizers may form part of a cascade refrigeration system.
100721 Fig. 3 is a process flow diagram of a single stage refrigeration
system 300
including a heat exchanger economizer 302. Like numbered items are as
described with
respect to Fig. 1. As shown in Fig. 3, the saturated liquid refrigerant 112
leaving the
accumulator 110 may be expanded across the expansion valve 102 to an
intermediate
pressure at which vapor and liquid may be separated, producing the refrigerant
mixture 114.
The refrigerant mixture 114 may be flowed into the chiller 104 at a
temperature lower than
the temperature to which the process stream 116 is to be cooled. The process
stream 116 may
be cooled within the chiller 104, as discussed above with respect to Fig. 1.

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10073] From the chiller 104, the saturated vapor refrigerant 118 may be
flowed through
the heat exchanger economizer 302. The cold, low-pressure saturated vapor
refrigerant 118
may be used to subcool the saturated liquid refrigerant 112 within the heat
exchanger
economizer 302. The superheated vapor refrigerant 304 exiting the heat
exchanger
5 economizer 302 may then be flowed through the compressor 106 and the
condenser 108, and
the resulting liquid refrigerant 120 may be stored within the accumulator 110,
as discussed
above with respect to Fig. 1.
lOW74] It is to be understood that the process flow diagram of Fig. 3 is
not intended to
indicate that the single stage refrigeration system 300 is to include all the
components shown
10 in Fig. 3. Further, the single stage refrigeration system 300 may
include any number of
additional components not shown in Fig. 3, depending on the details of the
specific
implementation.
I-0075] Fig. 4 is a process flow diagram of a cascade cooling system 400
including a first
refrigeration system 402 and a second refrigeration system 404. In various
embodiments, the
15 first refrigeration system 402 utilizes a refrigerant including a noble
gas, such as xenon or
krypton, while the second refrigeration system 404 may utilize a different
noble gas
refrigerant, a fluorocarbon refrigerant, or a hydrocarbon refrigerant. The
refrigerants in either
refrigeration system 402 or 404 may include mixtures. The cascade cooling
system 400 may
be used for instances in which a higher degree of cooling than that provided
by the
refrigeration systems 100, 200, or 300 is desired. The cascade cooling system
400 may
provide cooling at very low temperatures, e.g., below -40 C.
[0076] Within the first refrigeration system 402, a liquid refrigerant
stream 406 may be
flowed from an accumulator 408 through a first expansion valve 410 and a first
heat
exchanger 412, which chills a product stream 413. The resulting vapor/liquid
stream is
separated in a first flash drum 414. A portion of the liquid refrigerant
stream 406 may be
flowed directly into the first flash drum 414 via a bypass valve 416, which
can be used to
control the temperature of the liquid in the first flash drum 414, as well as
the amount of
cooling in the first heat exchanger 412.
10077] From the first flash drum 414, a liquid refrigerant stream 418 may
be flowed
through a second expansion valve 420, and flashed into a second heat exchanger
422, which
may be used to further chill the product stream 413. A gas accumulator 424
feeds the
resulting vapor refrigerant stream 426 to a first stage compressor 428. The
resulting medium
pressure vapor refrigerant stream 430 is combined with the vapor refrigerant
stream 432 from

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16
the first flash drum 414, and the combined stream is fed to a second stage
compressor 434.
The high pressure vapor stream 436 from the second stage compressor 434 is
passed through
a condenser 438, which may use cooling from the second refrigeration system
404.
Specifically, the condenser 438 may cool the high pressure vapor stream 436 to
produce a
liquid refrigerant stream 406 using a low temperature refrigerant stream 440
from the second
refrigeration system 404. The liquid refrigerant stream 406 from the condenser
438 is then
stored in the accumulator 408. A control valve 442 may be used to control the
flow of the
low temperature refrigerant stream 440 through the condenser 438. From the
condenser 438,
the resulting vapor refrigerant stream 444 back to the second refrigeration
system 404.
[0078] Within the second refrigeration system 404, a liquid refrigerant
stream 448 may
be flowed from an accumulator 450 through a heat exchanger 452 that is
configured to cool
the liquid refrigerant stream 448 via a chilling system 454. The resulting low
temperature
refrigerant stream 456 may be flowed through a first expansion valve 458 and a
first heat
exchanger 460, which chills the product stream 413. The resulting vapor/liquid
refrigerant
stream is separated in a first flash drum 462. A portion of the low
temperature refrigerant
stream 456 may be flowed directly into the first flash drum 462 via a bypass
valve 464, which
can be used to control the temperature of the liquid in the first flash drum
462, as well as the
amount of cooling in the first heat exchanger 460.
[0079] From the first flash drum 462, a liquid refrigerant stream 466 may
be flowed
through a second expansion valve 468, and flashed into a second heat exchanger
470, which
may be used to further chill the product stream 413. The resulting
vapor/liquid refrigerant
stream is separated in a second flash drum 472. A portion of the liquid
refrigerant stream 466
may be flowed directly into the second flash drum 472 via a bypass valve 474,
which can be
used to control the temperature of the liquid in the second flash drum 472, as
well as the
amount of cooling in the second heat exchanger 470.
[NW From the second flash drum 472, a liquid refrigerant stream 476
may be flowed
through a third expansion valve 478, and flashed into a third heat exchanger
480, which may
be used to further chill the product stream 413. A gas accumulator 482 feeds
the resulting
vapor refrigerant stream 484 to a first stage compressor 486. The resulting
medium pressure
vapor refrigerant stream 488 is combined with the vapor refrigerant stream 490
from the
second flash drum 472, and the combined stream is fed to a second stage
compressor 492.
The resulting high pressure vapor refrigerant stream 494 is combined with the
vapor
refrigerant mixture 496 from the first flash drum 462, and the combined stream
is fed to a

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third stage compressor 497. The resulting high pressure vapor refrigerant
stream 498 is
flowed through a heat exchanger 499, in which it may be further cooled through
indirect heat
exchange with cooling water. The resulting liquid refrigerant stream 448 may
then be flowed
into the accumulator 450.
1008/ It is to be understood that the process flow diagram of Fig. 4 is not
intended to
indicate that the cascade cooling system 400 is to include all the components
shown in Fig. 4.
Further, the cascade cooling system 400 may include any number of additional
components
not shown in Fig. 4, depending on the details of the specific implementation.
100821 Fig. 5 is process flow diagram of an expansion refrigeration
system 500 for
hydrocarbon dew point control. Condensation of heavy hydrocarbons, e.g., Cl-
C6, in natural
gas within pipes may result in an increase in pressure within the pipes, as
well as an increase
in the power usage of handling facilities. Therefore, the hydrocarbon dew
point may be
reduced using the expansion refrigeration system 500 in order to prevent such
condensation.
10083] As shown in Fig. 5, a dehydrated natural gas feed stream 502 may
be flowed into
a gas/gas heat exchanger 504. Within the gas/gas heat exchanger 504, the
dehydrated natural
gas feed stream 502 may be cooled through indirect heat exchange with a low
temperature
natural gas stream 506. The resulting natural gas stream 508 may be flowed
into a first
separator 510, which may remove some amount of heavy hydrocarbons 512 from the
natural
gas stream 508. In various embodiments, removing the heavy hydrocarbons 512
from the
natural gas stream 508 decreases the dew point of the natural gas stream 508.
The removed
heavy hydrocarbons 512 may be flowed out of the expansion refrigeration system
500
through a first outlet valve 514. For example, the heavy hydrocarbons 512 may
be flowed
from the expansion refrigeration system 500 to a stabilizer (not shown).
100841 The natural gas stream 508 may then be flowed into an expander
516. In various
embodiments, the expander 516 is a turbo-expander, which is a centrifugal or
axial flow
turbine. The expansion of the natural gas stream 508 within the expander 516
may provide
energy for driving a compressor 518, which is coupled to the expander 516 via
a shaft 520.
10085i From the expander 516, the resulting low temperature natural gas
stream 506 may
be flowed into a second separator 522, which may remove any remaining heavy
hydrocarbons 512 from the low temperature natural gas stream 506. In various
embodiments,
removing the heavy hydrocarbons 512 from the low temperature natural gas
stream 506
further decreases the dew point of the low temperature natural gas stream 506.
The removed

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heavy hydrocarbons 512 may then be flowed out of the expansion refrigeration
system 500
through a second outlet valve 524.
100861 The low temperature natural gas stream 506 may be flowed from the
second
separator 522 to the gas/gas heat exchanger 504, which may increase the
temperature of the
low temperature natural gas stream 506, producing a high temperature natural
gas stream
526. The high temperature natural gas stream 526 may then be flowed through
the
compressor 518, which may return the pressure of the natural gas stream 526 to
acceptable
sales gas pressure. The final, decreased dew point natural gas stream 528 may
then be flowed
out of the expansion refrigeration system 500.
100871 In an embodiment, a cooling system, for example, using a noble gas
refrigerant
may be used to add further cooling to the process. This cooling may be
implemented by
placing a heat exchanger 530 in the low temperature natural gas stream 506,
upstream of the
second separator 522. A refrigerant liquid 532 may be flashed across an
expansion valve
534, through the chiller 530. The resulting refrigerant vapor 536 can then be
returned to the
refrigerant system. The chilling may allow for the removal of a much higher
amount of
condensable hydrocarbons, such as C3s and higher. Further, in some
embodiments, the heat
exchanger 530 is placed upstream of the expander 516, with a separator located
between the
heat exchanger 530 and the expander 516 to prevent liquids from flowing into
the expander
516.
100881 It is to be understood that the process flow diagram of Fig. 5 is
not intended to
indicate that the expansion refrigeration system 500 is to include all the
components shown in
Fig. 5. Further, the expansion refrigeration system 500 may include any number
of additional
components not shown in Fig. 5, depending on the details of the specific
implementation.
100891 Fig. 6 is a process flow diagram of an expansion refrigeration
system 600 for
NGL extraction. In various embodiments, NGL extraction may be performed to
recover
NGLs, which include any number of different heavy hydrocarbons, from a natural
gas stream.
NGL extraction may be desirable due to the fact that NGLs are often of greater
value for
purposes other than as a gaseous heating fuel.
10090] A dry natural gas feed stream 602 may be flowed into a gas/gas
heat exchanger
604 from a dehydration system. Within the gas/gas heat exchanger 604, the dry
natural gas
feed stream 602 may be cooled through indirect heat exchange with a low
temperature natural
gas stream 606. The resulting natural gas stream 608 may be flowed into a
separator 610,

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19
which may remove a portion of NGLs 612 from the natural gas stream 608. The
removed
NGLs 612 may be flowed from the separator 610 to a deethanizer or demethanizer
614.
100911 The natural gas stream 608 may then be flowed into an expander
616. In various
embodiments, the expander 616 is a turbo-expander. The expansion of the
natural gas stream
608 within the expander 616 may provide energy for driving a compressor 618,
which is
coupled to the expander 616 via a shaft 620. In addition, the temperature of
the natural gas
stream 608 may be reduced via adiabatic expansion across a Joule-Thomson valve
622.
0092] From the expander 616, the resulting low temperature natural gas
stream 606 may
be flowed into the deethanizer or demethanizer 614. Within the deethanizer or
demethanizer
614, NGLs may be separated from the natural gas stream 606 and may be flowed
out of the
deethanizer or demethanizer 614 as an NGL product stream 624. The NGL product
stream
624 may then be pumped out of the expansion refrigeration system 600 via a
pump 626.
10093] The deethanizer or demethanizer 614 may be coupled to a heat
exchanger 628. In
some embodiments, the heat exchanger 628 is a reboiler 628 that may be used to
heat a
portion of a bottoms stream 630 from the deethanizer or demethanizer 614 via
indirect heat
exchange within a high temperature fluid 632. The heated bottoms stream 630
may then be
reinjected into the deethanizer or demethanizer 614.
10094] The separation of the NGL product stream 624 from the natural gas
stream 606
within the deethanizer or demethanizer 614 may result in the production of a
low temperature
natural gas stream that may be flowed out of the deethanizer or demethanizer
614 as an
overhead stream 634. The overhead stream 634 may be flowed into a heat
exchanger 636,
which may decrease the temperature of the overhead stream 634 through indirect
heat
exchange with a refrigerant mixture 638 including a noble gas. The decrease in
temperature
can lead to condensation of some of the vapors. The overhead stream 634 may
then be
separated within a separation vessel 640 to produce the low temperature
natural gas stream
606 and a liquid bottoms stream 642. The bottoms stream 642 may be pumped back
into the
deethanizer or demethanizer 614, via a pump 644, forming a recycle stream.
10095] The low temperature natural gas stream 606 may then be flowed
through the
gas/gas heat exchanger 604. The temperature of the low temperature natural gas
stream 506
may be increased within the gas/gas heat exchanger 604, producing a high
temperature
natural gas stream 646. The high temperature natural gas stream 646 may then
be flowed
through the compressor 618, which may increase the pressure of the natural gas
stream 646.

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In some embodiments, the high temperature natural gas stream 646 is also
flowed through a
second compressor 648, which may increase the pressure of the natural gas
stream 646 to
acceptable sales gas pressure. The natural gas product stream 650 may then be
flowed out of
the expansion refrigeration system 600.
5 10096l It is to be understood that the process flow diagram of Fig.
6 is not intended to
indicate that the expansion refrigeration system 600 is to include all the
components shown in
Fig. 6. Further, the expansion refrigeration system 600 may include any number
of additional
components not shown in Fig. 6, depending on the details of the specific
implementation.
10(071 Fig. 7 is a process flow diagram of an LNG production system 700.
As shown in
10 Fig. 7, LNG 702 may be produced from a natural gas stream 704 using a
number of different
refrigeration systems. As shown in Fig. 7, a portion of the natural gas stream
704 may be
separated from the natural gas stream 704 prior to entry into the LNG
production system 700,
and may be used as a fuel gas stream 706. The remaining natural gas stream 704
may be
flowed into an initial natural gas processing system 708. Within the natural
gas processing
15 system 708, the natural gas stream 704 may be purified and cooled. For
example, the natural
gas stream 704 may be cooled using noble gas refrigerants, e.g., refrigerant
mixtures
including one or more noble gases. For example, heavy hydrocarbons 710 may be
removed
from the natural gas stream 706, and may be used to produce gasoline 712
within a heavy
hydrocarbon processing system 714. In addition, any residual natural gas 716
that is
20 separated from the heavy hydrocarbons 710 during the production of the
gasoline 712 may be
returned to the natural gas stream 704.
10098] The natural gas stream 704 may be converted into the LNG 702
within a
cryogenic heat exchanger 718. In some embodiments, a mixed refrigerant stream
720 from a
mixed refrigeration system 722 is used to cool the natural gas stream 704
within the
cryogenic heat exchanger 718. According to embodiments described herein, the
mixed
refrigerant stream 720 is a refrigerant mixture including one or more noble
gases. In other
embodiments, a hydrocarbon refrigerant stream (not shown) from a hydrocarbon
refrigeration
system 724 is used to cool the natural gas stream 704 within the cryogenic
heat exchanger
718 to produce the LNG 702.
100991 It is to be understood that the process flow diagram of Fig. 7 is
not intended to
indicate that the LNG production system 700 is to include all the components
shown in Fig.
7. Further, the LNG production system 700 may include any number of additional

components not shown in Fig. 7, depending on the details of the specific
implementation.

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For example, any number of alternative refrigeration systems may also be used
to produce the
LNG 702 from the natural gas stream 704. In addition, any number of different
refrigeration
systems may be used in combination to produce the LNG 702.
Cascade Cooling Systems fbr the Production of Liquefied Natural Gas
[0100] Fig. 8 is a simplified process flow diagram of a cascade cooling
system 800. The
cascade cooling system 800 may be used to produce LNG 802 from a raw natural
gas 804.
The raw natural gas 804 may be flowed into an inlet scrubber 806 within the
cascade cooling
system 800. The inlet scrubber 806 may remove unwanted particulates from the
raw natural
gas 804. An inlet meter 808 may monitor the amount and characteristics of the
natural gas as
it enters the cascade cooling system 800. The natural gas may be passed
through an amine
treater 810, which can remove hydrogen sulfide, carbon dioxide, and other
unwanted gases
from the natural gas, and may be chilled within a heat exchanger 812 via
indirect heat
exchange with propane or any other suitable coolant.
[0101] The natural gas may be flowed through a first dehydrator 814,
which may remove
.. water 816 from the natural gas via a gravity separation process. The
removed water 816 may
be output from the cascade cooling system 800. The natural gas may then be
flowed to a
second dehydrator 818, which may remove any remaining water from the natural
gas. The
second dehydrator 818 may be, for example, a molecular sieve bed or a zeolite
bed.
[0102] A mercury removal system 820, which may include a molecular sieve
bed, may
remove mercury from the natural gas. In addition, a dry gas filter 822, such
as a pleated
paper filter, may remove any residual particulates from the natural gas.
[0103] From the dry gas filter 822, purified natural gas 823 may be sent
to a first cold box
824 within a refrigeration system 826. In this example, the first cold box 824
may function
as both a heat exchanger and a flash drum. However, in other implementations,
a separate
flash drum, such as the economizer 202 discussed with respect to Fig. 2, may
be used. Thus,
the first cold box 824 may cool the natural gas via indirect heat exchange
with a first
refrigerant mixture 828. The first refrigerant mixture 828 may be a
conventional refrigerant,
such as a HFC or propane. In addition, the first cold box 824 may act as a
vapor-liquid
separator, separating the first refrigerant mixture into a vapor refrigerant
mixture 830 and a
liquid refrigerant mixture. The vapor refrigerant mixture 830 may be generated
via flash
evaporation of the first refrigerant mixture 828 across an expansion valve
832. The
expansion valve 832 may throttle the first refrigerant mixture 828 to decrease
the pressure

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22
and temperature of the first refrigerant mixture 828, resulting in the flash
evaporation of the
first refrigerant mixture 828. In some embodiments, the first refrigerant
mixture 830 may be
entirely vaporized and, thus, no liquid refrigerant mixture may be present
within the first cold
box 824.
[0104] The first refrigerant mixture 828 may be continuously recirculated
and reused
within the refrigeration system 826. For example, after the first refrigerant
mixture 828
passes through the first cold box 824, the resulting vapor refrigerant mixture
830 is
compressed within a high pressure compressor 834 that can be powered by a
first gas turbine
836. The high pressure compressor 834 may be powered by a single gas turbine,
for
example, by being placed on a common or coupled shaft, or may be powered by
electric
motors The vapor refrigerant mixture 830 is then condensed into the liquid
refrigerant
mixture 828 within a first condenser 838. The liquid refrigerant mixture 828
may then be
stored within a surge tank 840, from which it may be flowed back into the
first cold box 824
to close the cooling cycle.
[0105] A second refrigerant mixture 842 can also be used to further cool
the purified
natural gas 823 within a second cold box 844. In this example, the second cold
box 834
further cools the purified natural gas 823 via indirect heat exchange with the
second
refrigerant mixture 842, which includes at least one noble gas. In addition,
the second cold
box 844 may act as a vapor-liquid separator, separating the second refrigerant
mixture 842
into a vapor refrigerant mixture 846 and a liquid refrigerant mixture. The
vapor refrigerant
mixture 846 may be generated via flash evaporation of the second refrigerant
mixture 842
across an expansion valve 848. The expansion valve 848 may throttle the second
refrigerant
mixture 842 to decrease the pressure and temperature of the second refrigerant
mixture 842,
resulting in the flash evaporation of the second refrigerant mixture 842. In
some
embodiments, the second refrigerant mixture 842 may be entirely vaporized and,
thus, no
liquid refrigerant mixture may be present within the second cold box 844.
[0106] The resulting vapor refrigerant mixture 846 exiting the second
cold box 844 may
be compressed within a low pressure compressor 850 that is powered by a second
gas turbine
852, producing a compressed refrigerant mixture 854. The low pressure
compressor 850 may
be powered by a single gas turbine, for example, by being placed on a common
or coupled
shaft, or may be powered by electric motors. The compressed refrigerant
mixture 854 may
then be condensed within a sub-ambient condenser 856, such as an ammonia
chiller, to
produce the second refrigerant mixture 842. The second refrigerant mixture 842
may be

23
stored within a surge tank 858, from which it may be flowed back into the
second cold box 844
to close the cooling cycle.
[0107] After the natural gas 823 has been cooled within the cold boxes
824 and 844, the
natural gas 823 may be further cooled and liquefied within an
autorefrigeration system 860,
producing the LNG 802. In some embodiments, the autorefrigeration system 860
includes a
series of expansion valves (not shown) and flash drums (not shown) that
progressively lower
the temperature and pressure of the natural gas until it reaches a liquid
state at, or near,
atmospheric pressure. In addition, prior to being flowed into the
autorefrigeration system 860,
the natural gas 823 may be flowed through a high pressure nitrogen rejection
unit (NRU) (not
shown). The NRU may remove some portion of the nitrogen from the natural gas
823 and,
thus, may allow for the use of a gas containing a high percentage of nitrogen.
[0108] The autorefrigeration system 860 may also produce natural gas
vapor, which may
be used as fuel 862. The fuel 862 may be compressed within a compressor 864
that is powered
by a third gas turbine 866 before being flowed out of the cascade cooling
system 800.
1 5 Depending on demand for fuel 862, a large portion of the natural gas
vapor may be recombined
with the initial purified natural gas 823, and returned to the system for
further processing.
[0109] The produced LNG 802 may be stored within an LNG tank 868 prior
to being sent
out of the cascade cooling system 800. Gases may be vented out of the LNG tank
868 and
pumped back into the autorefrigeration system 860 via a first pump 870. In
addition, gas 872
that is separated from the LNG 802 during loading of the LNG 802 at a loading
facility, for
example, may be pumped back into the autorefrigeration system 860 via a second
pump 874.
[0110] It is to be understood that the process flow diagram of Fig. 8 is
not intended to
indicate that the cascade cooling system 800 is to include all the components
shown in Fig. 8.
Further, the cascade cooling system 800 may include any number of additional
components not
shown in Fig. 8, depending on the details of the specific implementation.
[0111] Figs. 9A-B are a more detailed process flow diagram of a cascade
cooling system
900. The cascade cooling system 900 may be a cascade, open-loop liquefaction
system for the
production of LNG. The cascade cooling system 900 may operate at low
temperatures, e.g.,
below about 0 F, or below about -20 F, or below about -40 F. In addition,
the cascade cooling
system 900 may employ more than one refrigerant and provide refrigeration at
multiple
temperatures.
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[0112] The cascade cooling system 900 may include a first refrigeration
system 902, as
shown in Fig. 9A, which may utilize a non-hydrocarbon refrigerant such as a
hydrofluorocarbon, e.g., R-404A or R-410a. The cascade cooling system 900 may
also
include a second refrigeration system 904, as shown in Fig. 9B, which may
utilize a
refrigerant mixture including at least one noble gas, such as xenon, krypton,
argon, or
combinations thereof.
[0113] Fig. 10 is a more detailed process flow diagram of an
autorefrigeration system
1000. The autorefrigeration system 1000 may be located downstream of the
cascade cooling
system 900, as discussed further below.
[0114] A natural gas stream 908 may be flowed into a pipe joint 910 within
the cascade
cooling system 900. The pipe joint 910 may be configured to split the natural
gas stream 908
into two separate natural gas streams. One natural gas stream 914 may be
flowed into
another pipe joint 912, while the other natural gas stream 916 may be flowed
into the
autorefrigeration system 1000.
[0115] Within the pipe joint 912, the natural gas stream 914 may be
combined with a
natural gas vapor stream 1066 from the autorefrigeration system 1000. The
resulting natural
gas stream 918 may then be flowed into the first refrigeration system 902 in
preparation for
cooling of the natural gas stream 918. The natural gas stream 918 may be
cooled by being
passed through a series of heat exchangers 920, 922, 924, and 926 within the
first
refrigeration system 902. The heat exchangers 920, 922, 924, and 926 may also
be referred
to as evaporators, chillers, or cold boxes. The natural gas stream 918 may be
cooled within
each of the heat exchangers 920, 922, 924, and 926 through indirect heat
exchange with a
circulating non-hydrocarbon refrigerant. The non-hydrocarbon refrigerant may
be a
hydrofluorocarbon, such as R-404A or R-410A, or any other suitable type of non-

hydrocarbon refrigerant.
[0116] The non-hydrocarbon refrigerant may be continuously circulated
through the first
refrigeration system 902, which may continuously prepare the non-hydrocarbon
refrigerant
for entry into each of the heat exchangers 920, 922, 924, and 926. The non-
hydrocarbon
refrigerant may exit the first heat exchanger 920 via line 928 as a vapor non-
hydrocarbon
refrigerant. The vapor non-hydrocarbon refrigerant can be combined with
additional vapor
non-hydrocarbon refrigerant within a pipe joint 930. The vapor non-hydrocarbon
refrigerant
is then flowed through a compressor 932 to increase the pressure of the vapor
non-
hydrocarbon refrigerant, producing a superheated vapor non-hydrocarbon
refrigerant. The

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superheated vapor non-hydrocarbon refrigerant is flowed through a condenser
934, which
may cool and condense the superheated vapor non-hydrocarbon refrigerant,
producing a
liquid non-hydrocarbon refrigerant.
[0117] The liquid non-hydrocarbon refrigerant may be flowed through an
expansion
5 valve 935, which lowers the temperature and pressure of the liquid non-
hydrocarbon
refrigerant. This may result in the flash evaporation of the liquid non-
hydrocarbon
refrigerant, producing a mixture of the liquid non-hydrocarbon refrigerant and
a vapor non-
hydrocarbon refrigerant. The liquid non-hydrocarbon refrigerant and the vapor
non-
hydrocarbon refrigerant may be flowed into a first flash drum 936 via line
938. Within the
10 first flash drum 936, the liquid non-hydrocarbon refrigerant may be
separated from the vapor
non-hydrocarbon refrigerant.
[0118] The vapor non-hydrocarbon refrigerant may be flowed from the first
flash drum
936 to the pipe joint 930 via line 940. The liquid non-hydrocarbon refrigerant
may be flowed
into a pipe joint 942, which may split the liquid non-hydrocarbon refrigerant
into two
15 separate liquid non-hydrocarbon refrigerant streams. One liquid non-
hydrocarbon refrigerant
stream may be flowed through the first heat exchanger 920, partly or
completely flashed to
vapor, and returned to the pipe joint 930 via line 928. The other liquid non-
hydrocarbon
refrigerant stream may be flowed to a second flash drum 944 via line 946. The
line 946 may
also include an expansion valve 948 that throttles the liquid non-hydrocarbon
refrigerant
20 stream to control the flow of the liquid non-hydrocarbon refrigerant
stream into the second
flash drum 944. The throttling of the liquid non-hydrocarbon refrigerant
stream within the
expansion valve 948 may result in the flash evaporation of the liquid non-
hydrocarbon
refrigerant stream, producing a mixture of both vapor and liquid non-
hydrocarbon refrigerant.
[0119] The second flash drum 944 may separate the vapor non-hydrocarbon
refrigerant
25 from the liquid non-hydrocarbon refrigerant. The vapor non-hydrocarbon
refrigerant may be
flowed into a pipe joint 950 via line 952. The pipe joint 950 may combine the
vapor non-
hydrocarbon refrigerant with vapor non-hydrocarbon refrigerant recovered from
the second
and third heat exchangers 922 and 924. The combined vapor non-hydrocarbon
refrigerant
may be compressed within a compressor 954 and flowed into the pipe joint 930
via line 956
to be combined with the vapor from flash drum 936 and heat exchanger 920.
[0120] The liquid non-hydrocarbon refrigerant may be flowed from the
second flash
drum 944 to a pipe joint 958, which may split the liquid non-hydrocarbon
refrigerant into two
separate liquid non-hydrocarbon refrigerant streams. One liquid non-
hydrocarbon refrigerant

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26
stream is flowed through the second heat exchanger 922 and returned to the
pipe joint 950 via
line 960. The other liquid non-hydrocarbon refrigerant stream is flowed to a
third flash drum
962 via linc 964. The line 964 also includes an expansion valve 966 that
controls the flow of
the liquid non-hydrocarbon refrigerant stream into the third flash drum 962.
The expansion
valve 966 may result in the flash evaporation of the liquid non-hydrocarbon
refrigerant
stream, producing a mixture of both vapor and liquid non-hydrocarbon
refrigerant. Flashing
across the valve will reduce the temperature and pressure of the liquid non-
hydrocarbon
refrigerant stream.
[0121] The mixture of the vapor and liquid non-hydrocarbon refrigerant
may be flashed
into the third flash drum 962, further reducing the temperature and pressure.
The third flash
drum 962 may separate the vapor non-hydrocarbon refrigerant from the liquid
non-
hydrocarbon refrigerant. The vapor non-hydrocarbon refrigerant may be flowed
into a pipe
joint 968 via line 970. The pipe joint 968 may combine the vapor non-
hydrocarbon
refrigerant with vapor non-hydrocarbon refrigerant recovered from the third
and fourth heat
exchangers 924 and 926. The combined vapor non-hydrocarbon refrigerant may be
compressed within a compressor 972 and flowed into the pipe joint 950 via line
974.
[0122] The liquid non-hydrocarbon refrigerant may be flowed from the
third flash drum
962 to a pipe joint 976, which may split the liquid non-hydrocarbon
refrigerant into two
separate liquid non-hydrocarbon refrigerant streams. One liquid non-
hydrocarbon refrigerant
stream may be flowed through the third heat exchanger 924 and returned to the
pipe joint 968
via line 978. The other liquid non-hydrocarbon refrigerant stream may be
flowed through the
fourth heat exchanger 926 via line 980. The line 980 may also include an
expansion valve
982 that allows the liquid non-hydrocarbon refrigerant to flash, and, thus,
lowers the pressure
and temperature, of the liquid non-hydrocarbon refrigerant stream as it flows
into the fourth
heat exchanger 926. From the fourth heat exchanger 926, the liquid non-
hydrocarbon
refrigerant stream may be compressed within a compressor 984 and sent to the
pipe joint 968
via line 986.
[0123] In one embodiment, a refrigerant mixture including a noble gas is
precooled by
being flowed through each of the heat exchangers 920, 922, 924, and 926. The
refrigerant
mixture may be flowed from the second refrigeration system 904 to the heat
exchangers 920,
922, 924, and 926 within the first refrigeration system 902 via line 988, as
discussed further
below.

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[0124] After the natural gas stream has been progressively chilled within
each of the heat
exchangers 920, 922, 924, and 926, it is flowed into the second refrigeration
system 904,
shown in Fig. 9B, via line 990. The second refrigeration system 904 may
include a fifth heat
exchanger 992 and a sixth heat exchanger 994, which may be used to further
cool the natural
gas stream. The fifth heat exchanger 992 and the sixth heat exchanger 994 may
utilize a
refrigerant mixture including one or more noble gases, such as xenon or
krypton, to cool the
natural gas stream.
[0125] The refrigerant mixture may be continuously circulated through the
second
refrigeration system 904, which prepares the refrigerant mixture for entry
into each of the
heat exchangers 992 and 994. The refrigerant mixture may exit the fifth heat
exchanger 992
via line 996 as a vapor refrigerant mixture. The vapor refrigerant mixture may
be combined
with additional vapor refrigerant mixture within a pipe joint 998. The vapor
refrigerant
mixture may then be flowed through a compressor 1000, which may increase the
pressure of
the vapor refrigerant mixture, producing a superheated vapor refrigerant
mixture. The
superheated vapor refrigerant mixture may be flowed through a gas cooler 1002,
which may
cool the superheated vapor refrigerant mixture, producing a liquid refrigerant
mixture. In
some cases, if the vapor refrigerant mixture is below ambient temperature, the
vapor
refrigerant mixture may not be flowed through the gas cooler 1002. The liquid
refrigerant
mixture may then be flowed through the heat exchangers 920, 922, 924, and 926
within the
first refrigeration system 902 via line 988, as discussed above.
[0126] Once the refrigerant mixture has passed through the heat
exchangers 920, 922,
924, and 926, the refrigerant mixture may enter a fourth flash drum 1004
within the second
refrigeration system 904 via line 1006. Line 1006 may include an expansion
valve 1008 that
controls the flow of the refrigerant mixture into the fourth flash drum 1004.
The expansion
valve 1008 may reduce the temperature and pressure of the refrigerant mixture,
resulting in
the flash evaporation of the refrigerant mixture into both a vapor refrigerant
mixture and a
liquid refrigerant mixture.
[0127] The vapor refrigerant mixture and the liquid refrigerant mixture
may be flashed
into the fourth flash drum 1004, which may separate the vapor refrigerant
mixture from the
liquid refrigerant mixture. The vapor refrigerant mixture may be flowed into
the pipe joint
998 via line 1010. The liquid refrigerant mixture may be flowed from the
fourth flash drum
1004 to a pipe joint 1012, which may split the liquid refrigerant mixture into
two separate
liquid refrigerant mixture streams. One liquid refrigerant mixture stream may
be flowed

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28
through the fifth heat exchanger 992 and returned to the pipe joint 998 via
line 996. The
other liquid refrigerant mixture stream may be flowed through the sixth heat
exchanger 994
via line 1014. The line 1014 may also include an expansion valve 1016 that
controls the flow
of the liquid refrigerant mixture stream into the sixth heat exchanger 994,
e.g., by allowing
the refrigerant mixture to flash, lowering the temperature and creating a
vapor refrigerant
mixture and a liquid refrigerant mixture. From the sixth heat exchanger 994,
the resulting
vapor refrigerant mixture may be compressed within a compressor 1018 and then
flowed into
the pipe joint 998 to be recirculated.
[0128] After the natural gas stream has been cooled within the heat
exchangers 992 and
994 through indirect heat exchange with the refrigerant mixture including one
or more noble
gases, the natural gas stream may be flowed into the autorefrigeration system
1000, shown in
Fig. 10, via line 1020. The autorefrigeration system 1000 may include various
components
that are used to liquefy the natural gas, producing LNG.
[0129] The natural gas stream may be flowed into a pipe joint 1022, which
may combine
the natural gas stream from line 1020 with a portion of the natural gas stream
916. Initial
cooling of the natural gas may be performed within a heat exchanger 1024 prior
to flowing
the natural gas into the pipe joint 1022 via line 1026.
[0130] From the pipe joint 1022, the natural gas may be flowed into a
reboiler 1028,
which may decrease the temperature of the natural gas. The cooled natural gas
may be
expanded within a hydraulic expansion turbine 1030 and then flowed into a NRU
system
1032 via line 1034 to remove excess nitrogen from the natural gas. In various
embodiments,
the natural gas is flowed into a cryogenic fractionation column 1036, such as
a NRU tower,
within the NRU system 1032. In addition, heat may be transferred to the
cryogenic
fractionation column 1036 from the reboiler 1028 via line 1037.
[0131] The cryogenic fractionation column 1036 may separate nitrogen from
the natural
gas via a cryogenic distillation process. An overhead stream may be flowed out
of the
cryogenic fractionation column 1036 via line 1038. The overhead stream may
include
primarily methane and low boiling point or non-condensable gases, such as
nitrogen and
helium, which have been separated from the natural gas. The overhead stream
may be
flowed into an overhead condenser 1040, which may separate any liquid within
the overhead
stream and return it to the cryogenic fractionation column 1036 as reflux.
This may result in
the production of one vapor stream, a fuel stream including primarily methane
and another
vapor stream including primarily low boiling point gases. The fuel stream may
be flowed

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29
through the heat exchanger 1024 via line 1042. Within the heat exchanger 1024,
the
temperature of the vapor fuel stream may be increased via indirect heat
exchange with the
natural gas stream 916, producing a vapor fuel stream. The vapor fuel stream
may then be
compressed within a compressor 1044 and flowed out of the cascade cooling
system 900 as
fuel 1046 via line 1048. A liquid stream from the overhead condenser 1040 can
be returned
to the cryogenic fractionation column 1036 as a reflux stream.
[0132] The bottoms stream that is produced within the cryogenic
fractionation column
1036 includes primarily natural gas with traces of nitrogen. The bottoms
stream, as well as
the vapor stream from the overhead condenser 1040, may be flowed into a fifth
flash drum
1049 via lines 1050 and 1052, respectively. Line 1050 may also include an
expansion valve
1054 that controls the flow of the bottoms stream into the fifth flash drum
1049, allowing a
portion of the liquid from the bottoms stream to flash, creating a mixed phase
stream that is
flowed into the fifth flash drum 1049.
[0133] In addition, some portion of the bottoms stream may be flowed
through the
overhead condenser 1040 via line 1055. Line 1055 may also include an expansion
valve
1056 that controls the flow of the bottoms stream into the overhead condenser
1040. The
bottoms stream may be used as refrigerant for the overhead condenser 1040. The
resulting
vapor exiting the overhead condenser 1040 may be returned to the fifth flash
drum 1049 via
the line 1052.
[0134] The fifth flash drum 1049 may separate the mixed phase stream into a
vapor
stream that includes primarily natural gas and an LNG stream. The vapor stream
may be
flowed into a pipe joint 1058 via line 1060. The pipe joint 1058 may combine
the vapor
stream with another vapor stream recovered from a sixth flash drum 1062. The
combined
vapor streams may be compressed within a compressor 1064 and flowed into the
pipe joint
912 within the first refrigeration system 902 via line 1066.
[0135] The LNG stream may be flowed into the sixth flash drum 1062 via
line 1068. The
line 1068 may include an expansion valve 1070 that controls the flow of the
LNG stream into
the sixth flash drum 1062, allowing a portion of the liquid from the LNG
stream to flash,
creating a mixed phase system that is flowed into the sixth flash drum 1062.
[0136] The sixth flash drum 1062 may separate the mixed phase stream into
LNG and a
vapor stream that includes natural gas. The vapor stream may be flowed into a
pipe joint
1072 via line 1074. The pipe joint 1072 may combine the vapor stream with
another vapor

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stream recovered from a seventh flash drum 1076. The combined vapor streams
may be
compressed within a compressor 1078 and flowed into the pipe joint 1058.
[0137] The LNG stream may then be flowed into the seventh flash drum 1076
via line
1080. The line 1080 may include an expansion valve 1082 that controls the flow
of the LNG
5 stream into the seventh flash drum 1076, allowing a portion of the liquid
from the LNG to
flash. The seventh flash drum 1076 may further reduce the temperature and
pressure of the
LNG stream such that the LNG stream approaches an equilibrium temperature and
pressure,
as discussed below with respect to Fig. 11. The produced vapor stream may be
flowed into a
pipe joint 1084, which may combine the vapor stream with boil-off gas
recovered from an
10 .. LNG tank 1086. The combined vapor streams may be compressed within a
compressor 1088
and flowed into the pipe joint 1072.
[0138] The LNG tank 1086 may store the LNG stream for any period of time.
Boil-off
gas generated within the LNG tank 1086 may be flowed to the pipe joint 1084
via line 1090.
At any point in time, the LNG stream may be transported to an LNG tanker 1092
using a
15 pump 1094, for transport to markets. The additional boil-off gas 1098
generated while
loading LNG stream into the LNG tanker 1092, may be recovered in the cascade
cooling
system 900 by adding it to the pipe joint 1084.
[0139] It is to be understood that the process flow diagrams of Figs. 9A,
9B, and 10 are
not intended to indicate that the cascade cooling system 900 and the
autorefrigeration system
20 1000 are to include all the components shown in Figs. 9A, 9B, and 10.
Further, the cascade
cooling system 900 and/or the autorefrigeration system 1000 may include any
number of
additional components not shown in Figs. 9A, 9B, and 10, depending on the
details of the
specific implementation. For example, in some embodiments, the cascade cooling
system
900 includes one or more refrigeration systems that utilize a single mixed
refrigerant
25 including at least one noble gas. However, the cascade cooling system
900 and/or the
autorefrigeration system 1000 may also include any other types or combinations
of
refrigeration systems.
[0140] Fig. 11 is a schematic of a methane pressure-enthalpy (P-H)
diagram 1100. The
P-H diagram 1100 shows corresponding pressures 1102 and enthalpies 1104 at
various
30 temperatures. Like numbered items are as described with respect to Fig.
9. The P-H diagram
1100 includes an equilibrium curve 1106. A left side 1108 of the equilibrium
curve 1106
represents a pure liquid, while a right side of the equilibrium curve 1106
represents a pure gas
1110. In addition, if the pressure 1102 and enthalpy 1104 of the methane is
within the

CA 02867436 2014-09-15
WO 2013/148075 PCT/US2013/028906
31
equilibrium curve 1106, the methane exists as an equilibrium mixture of liquid
and gas. If
the pressure 1102 and enthalpy 1104 of methane is above the equilibrium curve
1106, the
methane is in a critical state.
[0141] According to the autorefrigeration process described herein, it is
desirable to
reduce the temperature and pressure 1102 of methane such that the methane
exists as a liquid
near atmospheric pressure. Each flash evaporation process within the expansion
valves 1056,
1070, and 1080 and the flash drums 1049, 1062, and 1076 isenthalpically
reduces the
temperature and the pressure of the methane. For example, prior to expansion
across the
hydraulic expansion turbine 1030, the methane may be in a critical state 1112.
In many
cases, it is difficult to reach such a critical state with typical hydrocarbon
refrigerants such as
methane. Therefore, xenon may be used for the autorefrigeration process
instead of methane
in some cases.
[0142] The hydraulic expansion turbine 1030 may isentropically reduce the
temperature
and the pressure 1102 of the methane to a first equilibrium state 1114. A NRU
may operate
at the first equilibrium state 1114 or at a slightly higher pressure. The
first equilibrium state
1114 may include a large liquid proportion 1116 and a small gas proportion
1118. The gas
may be vented out of the fifth flash drum 1049 such that the methane is in a
first pure liquid
state 1120. However, the first pure liquid state 1120 may be at a pressure
1102 that is
substantially higher than atmospheric pressure. Thus, the methane may be
flowed through
the expansion valve 1070 and into the sixth flash drum 1062.
[0143] The expansion valve 1070 may isenthalpically reduce the
temperature and the
pressure 1102 of the methane to a second equilibrium state 1122. Similarly to
the first
equilibrium state 1118, the second equilibrium state 1122 may include a large
liquid
proportion and a small gas proportion. The gas may be vented out of the sixth
flash drum
1062 such that the methane is in a second pure liquid state 1124. However, the
second pure
liquid state 1124 may still be at a pressure 1102 that is substantially higher
than atmospheric
pressure. Therefore, the methane may be flowed through the expansion valve
1080 and into
the seventh flash drum 1076.
[0144] The expansion valve 1082 may isenthalpically reduce the
temperature and the
pressure 1102 of the methane to a third equilibrium state 1126. The third
equilibrium state
1126 may include a large liquid proportion and a small gas proportion. The gas
may be
vented out of the seventh flash drum 1076 such that the methane is in a third
pure liquid state
1128. In various embodiments, the pressure 1102 of the third pure liquid state
1128 may be

CA 02867436 2014-09-15
WO 2013/148075 PCT/US2013/028906
32
near atmospheric pressure. Therefore, the methane may be in the final product
form, and
may be exported as LNG.
Method for LNG Formation
[0145] Fig. 12 is a process flow diagram of a method 1200 for the
formation of LNG. In
various embodiments, the method 1200 is implemented within any of the systems
800, 900,
or 1000 described above with respect to Figs. 8, 9, or 10, respectively.
[0146] The method 1200 begins at block 1202, at which the natural gas is
chilled in a
refrigeration system. The refrigeration system may be a mechanical
refrigeration system,
valve expansion system, turbine expansion system, or the like. The
refrigeration system uses
a refrigerant mixture including a noble gas. The noble gas may include xenon,
krypton,
argon, or any combinations thereof In addition, the refrigerant mixture may
include nitrogen
or a hydrocarbon, such as methane, ethane, propane, or butane. According to
embodiments
described herein, the refrigerant mixture including the noble gas is used in
any number of
cooling stages to achieve deeper cooling than provided by hydrocarbon
refrigerants.
[0147] In various embodiments, the refrigerant mixture is compressed to
provide a
compressed refrigerant mixture, and the compressed refrigerant mixture is
cooled by indirect
heat exchange with a cooling fluid. The compressed refrigerant mixture may be
expanded to
cool the compressed refrigerant mixture, thereby producing an expanded, cooled
refrigerant
mixture. The expanded, cooled refrigerant mixture may be passed to a heat
exchange area,
which may include, for example, a chiller or evaporator. In addition, the
natural gas may be
compressed and cooled by indirect heat exchange with an external cooling
fluid. The natural
gas may then be chilled within the heat exchange area using the expanded,
cooled refrigerant
mixture.
[0148] The natural gas may be chilled via one or more pre-cooling steps
using a first
refrigerant mixture. The first refrigerant mixture may include a noble gas,
nitrogen, or a
hydrocarbon, or any combinations thereof The natural gas may also be chilled
via one or
more deep cooling steps using a second refrigerant mixture. The second
refrigerant mixture
may include a noble gas, nitrogen, or a hydrocarbon, or any combinations
thereof
[0149] At block 1204, the natural gas is liquefied to form LNG in an
autorefrigeration
.. system. In various embodiments, the autorefrigeration system includes a
number of
expansion valves and flash drums that are used to cool and liquefy the natural
gas. The
natural gas may be flashed across an expansion valve, lowering the pressure
and temperature

CA 02867436 2014-09-15
33
of the natural gas and producing a vapor fraction and a liquid fraction. The
vapor
fraction and the liquid fraction may be flashed into a flash drum, which may
separate
the vapor fraction from the liquid fraction. This process may be repeated
within any
number of expansion valves and flash drums until a suitable amount of the
natural gas
has been converted to LNG.
[0150] It is to be understood that the process flow diagram of Fig. 12 is
not intended
to indicate that the steps of the method 1200 are to be executed in any
particular order,
or that all of the steps are to be included in every case. Further, any number
of
additional steps may be included within the method 1200, depending on the
details of
the specific implementation. For example, the natural gas may be cooled in a
first
refrigeration system prior to chilling the natural gas in the refrigeration
system. In
various embodiments, the first refrigeration system uses a non-hydrocarbon
refrigerant.
[0151] While the present techniques may be susceptible to various
modifications
and alternative forms, the embodiments discussed above have been shown only by
way
of example. However, it should again be understood that the techniques is not
intended
to be limited to the particular embodiments disclosed herein. Indeed, the
present
techniques include all alternatives, modifications, and equivalents falling
within the true
spirit and scope of the appended claims.

Representative Drawing
A single figure which represents the drawing illustrating the invention.
Administrative Status

For a clearer understanding of the status of the application/patent presented on this page, the site Disclaimer , as well as the definitions for Patent , Administrative Status , Maintenance Fee  and Payment History  should be consulted.

Administrative Status

Title Date
Forecasted Issue Date 2019-04-09
(86) PCT Filing Date 2013-03-04
(87) PCT Publication Date 2013-10-03
(85) National Entry 2014-09-15
Examination Requested 2018-01-18
(45) Issued 2019-04-09
Deemed Expired 2021-03-04

Abandonment History

There is no abandonment history.

Payment History

Fee Type Anniversary Year Due Date Amount Paid Paid Date
Application Fee $400.00 2014-09-15
Registration of a document - section 124 $100.00 2014-10-02
Maintenance Fee - Application - New Act 2 2015-03-04 $100.00 2015-02-19
Maintenance Fee - Application - New Act 3 2016-03-04 $100.00 2016-02-12
Maintenance Fee - Application - New Act 4 2017-03-06 $100.00 2017-02-16
Request for Examination $800.00 2018-01-18
Maintenance Fee - Application - New Act 5 2018-03-05 $200.00 2018-02-14
Maintenance Fee - Application - New Act 6 2019-03-04 $200.00 2019-02-19
Final Fee $300.00 2019-02-25
Maintenance Fee - Patent - New Act 7 2020-03-04 $200.00 2020-02-19
Owners on Record

Note: Records showing the ownership history in alphabetical order.

Current Owners on Record
EXXONMOBIL UPSTREAM RESEARCH COMPANY
Past Owners on Record
None
Past Owners that do not appear in the "Owners on Record" listing will appear in other documentation within the application.
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Document
Description 
Date
(yyyy-mm-dd) 
Number of pages   Size of Image (KB) 
Abstract 2014-09-15 2 65
Claims 2014-09-15 4 168
Drawings 2014-09-15 13 543
Description 2014-09-15 37 2,085
Representative Drawing 2014-09-15 1 12
Cover Page 2014-12-03 1 36
Request for Examination 2018-01-18 1 29
Description 2014-09-16 33 1,793
Claims 2014-09-16 6 239
Description 2018-01-23 33 1,783
Claims 2018-01-23 5 157
PPH OEE 2018-01-23 9 383
PPH Request 2018-01-23 11 461
International Preliminary Examination Report 2014-09-16 14 730
Claims 2014-09-17 4 155
Examiner Requisition 2018-03-09 4 208
Amendment 2018-04-03 25 685
Drawings 2018-04-03 13 277
Claims 2018-04-03 5 172
Examiner Requisition 2018-06-13 3 134
Amendment 2018-07-16 11 392
Claims 2018-07-16 5 170
Examiner Requisition 2018-10-01 3 181
Amendment 2018-10-12 11 410
Claims 2018-10-12 5 174
Final Fee 2019-02-25 2 46
Representative Drawing 2019-03-07 1 6
Cover Page 2019-03-07 1 33
PCT 2014-09-15 3 148
Assignment 2014-09-15 8 275
Prosecution-Amendment 2014-09-15 8 427
Assignment 2014-10-02 5 395