U.S. patent application number 14/437168 was filed with the patent office on 2015-10-08 for liquefaction of natural gas.
The applicant listed for this patent is Russell H. Oelfke, Jorge Vincentelli. Invention is credited to Russell H. Oelfke, Jorge Vincentelli.
Application Number | 20150285553 14/437168 |
Document ID | / |
Family ID | 50731605 |
Filed Date | 2015-10-08 |
United States Patent
Application |
20150285553 |
Kind Code |
A1 |
Oelfke; Russell H. ; et
al. |
October 8, 2015 |
Liquefaction of Natural Gas
Abstract
Systems and a method for the formation of a liquefied natural
gas (LNG) are disclosed herein. The system includes a first
fluorocarbon refrigeration system configured to chill a natural gas
using a first fluorocarbon refrigerant and a second fluorocarbon
refrigeration system configured to further chill the natural gas
using a second fluorocarbon refrigerant. The system also includes a
nitrogen refrigeration system configured to cool the natural gas
using a nitrogen refrigerant to produce LNG and a nitrogen
rejection unit configured to remove nitrogen from the LNG. As an
alternative embodiment, the nitrogen refrigeration system can be
replaced by a methane autorefrigeration system.
Inventors: |
Oelfke; Russell H.;
(Houston, TX) ; Vincentelli; Jorge; (Arlington,
VA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Oelfke; Russell H.
Vincentelli; Jorge |
Houston
Arlington |
TX
VA |
US
US |
|
|
Family ID: |
50731605 |
Appl. No.: |
14/437168 |
Filed: |
November 1, 2013 |
PCT Filed: |
November 1, 2013 |
PCT NO: |
PCT/US13/67919 |
371 Date: |
April 20, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61727577 |
Nov 16, 2012 |
|
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Current U.S.
Class: |
62/611 |
Current CPC
Class: |
F25J 2210/06 20130101;
F25J 1/0219 20130101; F25J 1/0264 20130101; F25J 2245/02 20130101;
F25J 1/0035 20130101; F25J 1/021 20130101; F25J 2220/64 20130101;
F25J 1/0045 20130101; F25J 1/0265 20130101; F25J 1/004 20130101;
F25J 1/0022 20130101; F25J 1/0218 20130101; F25J 1/005 20130101;
F25J 1/0097 20130101; F25J 2210/04 20130101; F25J 1/0207 20130101;
F25J 1/0052 20130101; F25J 1/0072 20130101; F25J 2220/62 20130101;
F25J 2270/16 20130101 |
International
Class: |
F25J 1/00 20060101
F25J001/00 |
Claims
1. A hydrocarbon processing system for formation of a liquefied
natural gas (LNG), comprising: a first fluorocarbon refrigeration
system configured to chill a natural gas using a first fluorocarbon
refrigerant; a second fluorocarbon refrigeration system configured
to further chill the natural gas using a second fluorocarbon
refrigerant; a nitrogen refrigeration system configured to cool the
natural gas using a nitrogen refrigerant to produce LNG; and a
nitrogen rejection unit configured to remove nitrogen from the
LNG.
2. The hydrocarbon processing system of claim 1, wherein the first
fluorocarbon refrigeration system is configured to cool the second
fluorocarbon refrigerant of the second fluorocarbon refrigeration
system.
3. The hydrocarbon processing system of claim 1, wherein the first
fluorocarbon refrigeration system or the second fluorocarbon
refrigeration system, or both, is configured to cool the nitrogen
refrigerant of the nitrogen refrigeration system.
4. The hydrocarbon processing system of claim 1, wherein the first
fluorocarbon refrigeration system or the second fluorocarbon
refrigeration system, or both, comprises multiple cooling
cycles.
5. The hydrocarbon processing system of claim 1, wherein the
nitrogen refrigeration system comprises a plurality of heat
exchangers configured to allow for cooling of the natural gas via
an indirect exchange of heat between the natural gas and the
nitrogen refrigerant.
6. The hydrocarbon processing system of claim 1, wherein the first
fluorocarbon refrigeration system comprises: a compressor
configured to compress the first fluorocarbon refrigerant to
provide a compressed first fluorocarbon refrigerant; a chiller
configured to cool the compressed first fluorocarbon refrigerant by
indirect heat exchange with a cooling fluid; a valve configured to
expand the compressed first fluorocarbon refrigerant to cool the
compressed first fluorocarbon refrigerant, thereby producing a
cooled first fluorocarbon refrigerant; and a heat exchanger
configured to cool the natural gas via indirect heat exchange with
the cooled first fluorocarbon refrigerant.
7. The hydrocarbon processing system of claim 1, wherein the second
fluorocarbon refrigeration system comprises: a compressor
configured to compress the second fluorocarbon refrigerant to
provide a compressed second fluorocarbon refrigerant; a chiller
configured to cool the compressed second fluorocarbon refrigerant
by indirect heat exchange with a cooling fluid; a valve configured
to expand the compressed second fluorocarbon refrigerant to cool
the compressed second fluorocarbon refrigerant, thereby producing a
cooled second fluorocarbon refrigerant; and a heat exchanger
configured to cool the natural gas via indirect heat exchange with
the cooled second fluorocarbon refrigerant.
8. The hydrocarbon processing system of claim 1, wherein the first
fluorocarbon refrigerant comprises R-410A.
9. The hydrocarbon processing system of claim 1, wherein the second
fluorocarbon refrigerant comprises R-508B.
10. The hydrocarbon processing system of claim 1, wherein the first
fluorocarbon refrigerant or the second fluorocarbon refrigerant, or
both, comprises a nontoxic, nonflammable refrigerant.
11. The hydrocarbon processing system of claim 1, wherein the first
fluorocarbon refrigeration system or the second fluorocarbon
refrigeration system, or both, comprises two or more chillers and
two or more compressors.
12. The hydrocarbon processing system of claim 1, wherein the first
fluorocarbon refrigeration system and the second fluorocarbon
refrigeration system are implemented in series.
13. The hydrocarbon processing system of claim 1, wherein the
nitrogen refrigerant is in a gas phase.
14. The hydrocarbon processing system of claim 1, wherein the
nitrogen refrigeration system comprises two or more chillers, two
or more expanders, and two or more compressors.
15. The hydrocarbon processing system of claim 1, wherein the
hydrocarbon processing system is configured to chill the natural
gas for hydrocarbon dew point control.
16. The hydrocarbon processing system of claim 1, wherein the
hydrocarbon processing system is configured to chill the natural
gas for natural gas liquid extraction.
17. The hydrocarbon processing system of claim 1, wherein the
hydrocarbon processing system is configured to separate methane and
lighter gases from carbon dioxide and heavier gases.
18. The hydrocarbon processing system of claim 1, wherein the
hydrocarbon processing system is configured to prepare hydrocarbons
for liquefied petroleum gas production storage.
19. The hydrocarbon processing system of claim 1, wherein the
hydrocarbon processing system is configured to condense a reflux
stream.
20. A method for formation of a liquefied natural gas (LNG),
comprising: cooling a natural gas in a first fluorocarbon
refrigeration system; cooling the natural gas in a second
fluorocarbon refrigeration system; liquefying the natural gas to
form LNG in a nitrogen refrigeration system; and removing nitrogen
from the LNG in a nitrogen rejection unit.
21. The method of claim 20, comprising cooling a second
fluorocarbon refrigerant of the second fluorocarbon refrigeration
system within the first fluorocarbon refrigeration system.
22. The method of claim 20, comprising cooling a nitrogen
refrigerant of the nitrogen refrigeration system within the first
fluorocarbon refrigeration system or the second fluorocarbon
refrigeration system, or both.
23. The method of claim 20, wherein cooling the natural gas in the
first fluorocarbon refrigeration system comprises: compressing a
first fluorocarbon refrigerant to provide a compressed first
fluorocarbon refrigerant; optionally cooling the compressed first
fluorocarbon refrigerant by indirect heat exchange with a cooling
fluid; expanding the compressed first fluorocarbon refrigerant to
cool the compressed first fluorocarbon refrigerant, thereby
producing an expanded, cooled first fluorocarbon refrigerant;
passing said expanded, cooled first fluorocarbon refrigerant to a
first heat exchange area; optionally compressing the natural gas;
optionally cooling the natural gas by indirect heat exchange with
an external cooling fluid; and heat exchanging the natural gas with
the expanded, cooled first fluorocarbon refrigerant.
24. The method of claim 20, wherein cooling the natural gas in the
second fluorocarbon refrigeration system comprises: compressing a
second fluorocarbon refrigerant to provide a compressed second
fluorocarbon refrigerant; optionally cooling the compressed second
fluorocarbon refrigerant by indirect heat exchange with a cooling
fluid; expanding the compressed second fluorocarbon refrigerant to
cool the compressed second fluorocarbon refrigerant, thereby
producing an expanded, cooled second fluorocarbon refrigerant;
passing said expanded, cooled second fluorocarbon refrigerant to a
first heat exchange area; optionally compressing the natural gas;
optionally cooling the natural gas by indirect heat exchange with
an external cooling fluid; and heat exchanging the natural gas with
the expanded, cooled second fluorocarbon refrigerant.
25. The method of claim 20, comprising maintaining a nitrogen
refrigerant of the nitrogen refrigeration system in a gas phase
using one or more expansion turbines.
26. The method of claim 20, comprising chilling the natural gas in
the first fluorocarbon refrigeration system or the second
fluorocarbon refrigeration system, or both, using two or more
refrigeration stages.
27. The method of claim 20, comprising liquefying the natural gas
in the nitrogen refrigeration system using one or more
refrigeration stages.
28. A hydrocarbon processing system for formation of a liquefied
natural gas (LNG), comprising: a first refrigeration system
configured to cool a natural gas using a first fluorocarbon
refrigerant, wherein the first refrigeration system comprises a
plurality of first heat exchangers configured to allow for cooling
of the natural gas via an indirect exchange of heat between the
natural gas and the first fluorocarbon refrigerant; a second
refrigeration system configured to chill the natural gas using a
second fluorocarbon refrigerant, wherein the second refrigeration
system comprises a plurality of second heat exchangers configured
to allow for cooling of the natural gas via an indirect exchange of
heat between the natural gas and the second fluorocarbon
refrigerant; a third refrigeration system configured to form LNG
from the natural gas using a nitrogen refrigerant, wherein the
third refrigeration system comprises a plurality of third heat
exchangers configured to allow for cooling of the natural gas via
an indirect exchange of heat between the natural gas and the
nitrogen refrigerant; and a nitrogen rejection unit configured to
remove nitrogen from the LNG.
29. The hydrocarbon processing system of claim 28, wherein the
nitrogen refrigerant is in a gas phase.
30. The hydrocarbon processing system of claim 28, wherein the
plurality of first heat exchangers comprise evaporators configured
to cool the natural gas by at least partially vaporizing the first
fluorocarbon refrigerant via a transfer of heat from the natural
gas to the first fluorocarbon refrigerant.
31. The hydrocarbon processing system of claim 28, wherein the
plurality of second heat exchangers comprise evaporators configured
to chill the natural gas by at least partially vaporizing the
second fluorocarbon refrigerant via a transfer of heat from the
natural gas to the second fluorocarbon refrigerant.
32. A hydrocarbon processing system for formation of a liquefied
natural gas (LNG), comprising: a first fluorocarbon refrigeration
system configured to chill a natural gas using a first fluorocarbon
refrigerant; a second fluorocarbon refrigeration system configured
to further chill the natural gas using a second fluorocarbon
refrigerant; and a methane autorefrigeration system configured to
cool the natural gas to produce LNG.
33. The hydrocarbon processing system of claim 32, comprising a
nitrogen rejection unit upstream of the methane autorefrigeration
system, and wherein the methane autorefrigeration system comprises
a plurality of expansion valves and a plurality of flash drums.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application 61/727,577 filed Nov. 16, 2012 entitled
LIQUEFACTION OF NATURAL GAS, the entirety of which is incorporated
by reference herein.
FIELD OF THE INVENTION
[0002] The present techniques relate generally to the field of
hydrocarbon recovery and treatment processes and, more
particularly, to a method and systems for forming liquefied natural
gas (LNG) via a refrigeration process that includes two
fluorocarbon refrigeration cycles upstream of a nitrogen
refrigeration cycle or a methane autorefrigeration cycle.
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,
in many cases, it is desirable to implement a refrigeration system
that uses nonflammable refrigerants.
[0005] U.S. Pat. No. 6,412,302 to Foglietta et al. describes a
process for producing a liquefied natural gas stream. The process
includes cooling at least a portion of a pressurized natural gas
feed stream by heat exchange contact with first and second expanded
refrigerants that are used in independent refrigeration cycles. The
first expanded refrigerant is selected from methane, ethane, and
treated and pressurized natural gas, while the second expanded
refrigerant is nitrogen. However, as discussed herein, it may be
desirable to produce a LNG stream within a refrigeration system
that uses nonflammable refrigerants.
SUMMARY
[0006] An embodiment provides a hydrocarbon processing system for
the formation of a liquefied natural gas (LNG). The hydrocarbon
processing system includes a first fluorocarbon refrigeration
system configured to chill a natural gas using a first fluorocarbon
refrigerant and a second fluorocarbon refrigeration system
configured to further chill the natural gas using a second
fluorocarbon refrigerant. The hydrocarbon processing system also
includes a nitrogen refrigeration system configured to cool the
natural gas using a nitrogen refrigerant to produce LNG and a
nitrogen rejection unit configured to remove nitrogen from the
LNG.
[0007] Another embodiment provides a method for the formation of
LNG. The method includes cooling a natural gas in a first
fluorocarbon refrigeration system, cooling the natural gas in a
second fluorocarbon refrigeration system, liquefying the natural
gas to form LNG in a nitrogen refrigeration system, and removing
nitrogen from the LNG in a nitrogen rejection unit.
[0008] Another embodiment provides a hydrocarbon processing system
for the formation of LNG. The hydrocarbon processing system
includes a first refrigeration system configured to cool a natural
gas using a first fluorocarbon refrigerant, wherein the first
refrigeration system includes a number of first heat exchangers
configured to allow for cooling of the natural gas via an indirect
exchange of heat between the natural gas and the first fluorocarbon
refrigerant. The hydrocarbon processing system includes a second
refrigeration system configured to chill the natural gas using a
second fluorocarbon refrigerant, wherein the second refrigeration
system includes a number of second heat exchangers configured to
allow for cooling of the natural gas via an indirect exchange of
heat between the natural gas and the second fluorocarbon
refrigerant. The hydrocarbon processing system also includes a
third refrigeration system configured to form LNG from the natural
gas using a nitrogen refrigerant, wherein the third refrigeration
system includes a number of third heat exchangers configured to
allow for cooling of the natural gas via an indirect exchange of
heat between the natural gas and the nitrogen refrigerant. The
hydrocarbon processing system further includes a nitrogen rejection
unit configured to remove nitrogen from the LNG.
[0009] Another embodiment provides a hydrocarbon processing system
for the formation of LNG. The hydrocarbon processing system
includes a first fluorocarbon refrigeration system configured to
chill a natural gas using a first fluorocarbon refrigerant, a
second fluorocarbon refrigeration system configured to further
chill the natural gas using a second fluorocarbon refrigerant, and
a methane autorefrigeration system configured to cool the natural
gas to produce LNG.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The advantages of the present techniques are better
understood by referring to the following detailed description and
the attached drawings, in which:
[0011] FIG. 1 is a process flow diagram of a single stage
refrigeration system;
[0012] FIG. 2 is a process flow diagram of a two stage
refrigeration system including an economizer;
[0013] FIG. 3 is a process flow diagram of a single stage
refrigeration system including a heat exchanger economizer;
[0014] FIG. 4 is a process flow diagram of a cascade cooling system
including a first refrigeration system and a second refrigeration
system;
[0015] FIG. 5 is process flow diagram of an expansion refrigeration
system for hydrocarbon dew point control;
[0016] FIG. 6 is a process flow diagram of an expansion
refrigeration system for NGL production;
[0017] FIG. 7 is a process flow diagram of a LNG production
system;
[0018] FIGS. 8A and 8B are process flow diagrams of a cascade
fluorocarbon with nitrogen refrigeration cooling system;
[0019] FIG. 9 is a process flow diagram of a system including a
NRU;
[0020] FIGS. 10A and 10B are process flow diagrams of another
cascade fluorocarbon with nitrogen refrigeration cooling
system;
[0021] FIG. 10C is a process flow diagram of an alternative
embodiment of the cascade fluorocarbon with nitrogen refrigeration
cooling system with a simplified nitrogen refrigeration system;
[0022] FIGS. 11A and 11B are process flow diagrams of another
cascade cooling system;
[0023] FIG. 11C is a process flow diagram of an autorefrigeration
system that is implemented within the same hydrocarbon processing
system as the cascade cooling system of FIGS. 11A and 11B;
[0024] FIG. 12 is a process flow diagram of a method for the
formation of LNG from a natural gas stream; and
[0025] FIG. 13 is a process flow diagram of another method for the
formation of LNG from a natural gas stream.
DETAILED DESCRIPTION
[0026] 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 herein, but rather, include all alternatives,
modifications, and equivalents falling within the spirit and scope
of the appended claims.
[0027] 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 herein, 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 herein, 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.
[0028] As used herein, "autorefrigeration" refers to a process
whereby a portion of a product stream is used for refrigeration
purposes. This is achieved by extracting a fraction of the product
stream prior to final cooling for the purpose of providing
refrigeration capacity. This extracted stream is expanded in a
valve or expander and, as a result of the expansion, the
temperature of the stream is lowered. This stream is used for
cooling the product stream in a heat exchanger. After exchanging
heat, this stream is recompressed and blended with the feed gas
stream. This process is also known as open cycle refrigeration.
[0029] Alternatively, "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 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 "flash evaporation."
[0030] 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.
[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.
[0032] 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. C., at least about 5.degree. C., at
least about 10.degree. C., at least about 15.degree. C., at least
about 25.degree. C., at least about 50.degree. C., at least about
100.degree. C., 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, brazed aluminum, spiral wound, and/or the like. In the
alternative, the cooling may use evaporative (heat of vaporization)
cooling, sensible heat cooling, and/or direct heat exchange, such
as a liquid sprayed directly into a process stream.
[0033] "Cryogenic temperature" refers to a temperature that is
about -50.degree. C. or below.
[0034] 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 ethane and heavier components. The methane fraction
is typically recovered as purified gas that contains small amounts
of inert gases such as nitrogen, CO.sub.2, or the like.
[0035] "Fluorocarbons," also referred to as "perfluorocarbons" or
"PFCs," are molecules including F and C atoms. Fluorocarbons have
F--C bonds and, depending on the number of carbon atoms in the
species, C--C bonds. An example of a fluorocarbon includes
hexafluoroethane (C.sub.2F.sub.6). "Hydrofluorocarbons" or "HFCs"
are a specific type of fluorocarbon 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 (CHF.sub.3),
pentafluoroethane (C.sub.2HF.sub.5), tetrafluoroethane
(C.sub.2H.sub.2F.sub.4), heptafluoropropane (C.sub.3HF.sub.7),
hexafluoropropane (C.sub.3H.sub.2F.sub.6), pentafluoropropane
(C.sub.3H.sub.3F.sub.5), and tetrafluoropropane
(C.sub.3H.sub.4F.sub.4), among other compounds of similar chemical
structure.
[0036] 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.
[0037] 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
shell-and-tube, spiral, hairpin, core, core-and-kettle,
double-pipe, brazed aluminum, spiral wound, 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 there through, and to affect direct
or indirect heat exchange between one or more lines of refrigerant,
and one or more feed streams.
[0038] 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.
[0039] "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.
[0040] "Liquefied petroleum as" or "LPG" generally refers to a
mixture of propane, butane, and other light hydrocarbons derived
from refining crude oil. At normal temperature, LPG is a gas.
However, LPG can be cooled or subjected to pressure to facilitate
storage and transportation.
[0041] "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
component, 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, butane and butylene isomers, as well
as pentanes. Non-hydrocarbon components generally employed in mixed
refrigerants can include nitrogen. Mixed refrigerant processes
employ at least one mixed component refrigerant, but can
additionally employ one or more pure-component refrigerants as
well.
[0042] "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 (CH.sub.4) 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
(C.sub.2H.sub.6), higher molecular weight hydrocarbons (e.g.,
C.sub.3-C.sub.20 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 or freeze during the cooling process.
[0043] As used herein, "natural gas liquids" (NGLs) refer to
mixtures of hydrocarbons whose components are, for example,
typically heavier than methane and condensed from a natural gas.
Some examples of hydrocarbon components of NGL streams include
ethane, propane, butane, and pentane isomers, benzene, toluene, and
other aromatic compounds.
[0044] A "nitrogen rejection unit" or "NRU" refers to any system or
device configured to receive a natural gas feed stream and produce
substantially pure products streams, e.g., a salable methane stream
and a nitrogen stream including about 30% to 99% N.sub.2. Examples
of types of NRU's include cryogenic distillation, pressure swing
adsorption (PSA), membrane separation, lean oil absorption, and
solvent absorption.
[0045] 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.
[0046] Refrigerant components often include single component
refrigerants. A single component refrigerant with a single
halogenated hydrocarbon has an associated "R-" designation of two
or three numbers, which reflects its chemical composition. Adding
90 to the number gives three digits that stand for the number of
carbon, hydrogen, and fluorine atoms, respectively. The first digit
of a refrigerant with three numbers is one unit lower than the
number of carbon atoms in the molecule. If the molecule contains
only one carbon atom, the first digit is omitted. The second digit
is one unit greater than the number of hydrogen atoms in the
molecule. The third digit is equal to the number of fluorine atoms
in the molecule. Remaining bonds not accounted for are occupied by
chlorine atoms. A suffix of a lower-case letter "a," "b," or "c"
indicates increasingly unsymmetrical isomers. As a special case,
the R-400 series is made up of zeotropic blends, and the R-500
series is made up of so-called azeotropic blends. The rightmost
digit is assigned arbitrarily by ASHRAE, an industry
organization.
[0047] "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.
[0048] Overview
[0049] Embodiments described herein provide a hydrocarbon
processing system. The hydrocarbon processing system includes a
refrigeration system, such as a cascade cooling system, for
producing LNG from a natural gas. The refrigeration system includes
two fluorocarbon refrigeration systems and a nitrogen or methane
refrigeration system. The fluorocarbon refrigeration systems and
the nitrogen or methane refrigeration system are used to cool the
natural gas, producing LNG. In addition, the hydrocarbon processing
system may include a NRU, which may be used to remove nitrogen from
the produced LNG.
[0050] Hydrocarbon processing systems include any number of 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 CO.sub.2
removal, LPG production storage, condensation of reflux in
deethanizers/demethanizers, and natural gas liquefaction to produce
LNG.
[0051] 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 a corresponding reduction in temperature. Natural gas
liquefaction cycles may also use variations or combinations of
these three cycles.
[0052] LNG is prepared from a feed gas by refrigeration and
liquefaction technologies. Optional steps include condensate
removal, CO.sub.2 removal, dehydration, mercury removal, nitrogen
stripping, H.sub.2S removal, and the like. After liquefaction, LNG
may be stored or loaded on a tanker for sale or transport.
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.
[0053] Carbon dioxide removal, i.e., separation of methane and
lighter gases from CO.sub.2 and heavier gases, may be achieved with
cryogenic distillation processes, such as the Controlled Freeze
Zone technology available from ExxonMobil Corporation.
[0054] 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 deethanizers
and/or demethanizers, among others.
[0055] Refrigerants
[0056] 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 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. Commercially available refrigerants including fluorocarbons
(FCs) or hydrofluorocarbons (HFCs) are used in various
applications. Exemplary refrigerants are commercially available
from DuPont Corporation, including the ISCEON.RTM. family of
refrigerants, the SUVA.RTM. family of refrigerants, the OPTEON.RTM.
family of refrigerants, and the FREON.RTM. family of
refrigerants.
[0057] 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.
R-508B is a blend of R-23 and R-116.
[0058] 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 herein.
[0059] Refrigeration Systems
[0060] 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.
[0061] 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 such as a
fluorocarbon. Further, in various embodiments, the single stage
refrigeration system 100 is implemented upstream of a nitrogen
refrigeration or methane autorefrigeration system including a NRU.
Multiple single stage refrigeration systems 100 may also be
implemented in series upstream of such a nitrogen refrigeration
system or a methane autorefrigeration system.
[0062] 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 vaporizes,
creating a saturated vapor refrigerant 118.
[0063] After leaving the chiller 104, the saturated vapor
refrigerant 118 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 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.
[0064] 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.
[0065] 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. In various
embodiments, the two stage refrigeration system 200 utilizes a
refrigerant such as a fluorocarbon. Further, in various
embodiments, the two stage refrigeration system 200 is implemented
upstream of a nitrogen refrigeration or a methane autorefrigeration
system including a NRU. Multiple two stage refrigeration systems
200 may also be implemented in series upstream of such a nitrogen
refrigeration system or a methane autorefrigeration system.
[0066] 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. Heat exchange economizers utilize a
number of heat exchangers to transfer heat between process streams.
This may reduce the amount of energy input into the two stage
refrigeration system 200 by heat integrating process streams with
each other.
[0067] 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. For example, as the saturated liquid refrigerant 112
flashes across the expansion valve 102, a vapor refrigerant 204 and
a 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.
[0068] 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 will have a
higher liquid content than 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.
[0069] 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
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 with respect to
FIG. 1.
[0070] 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.
[0071] 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.
[0072] 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. In
various embodiments, the single stage refrigeration system 300
utilizes a refrigerant such as a fluorocarbon. Further, in various
embodiments, the single stage refrigeration system 300 is
implemented upstream of a nitrogen refrigeration system or a
methane autorefrigeration system including a NRU. Multiple single
stage refrigeration systems 300 may also be implemented in series
upstream of such a nitrogen refrigeration system or a methane
autorefrigeration system.
[0073] 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 with respect to FIG. 1.
[0074] 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 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 with respect to FIG. 1.
[0075] 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 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.
[0076] 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 first
refrigeration system 402 and the second refrigeration system 404
utilize fluorocarbon refrigerants. For example, the first
refrigeration system 402 may utilize R-410A, and the second
refrigeration system 404 may utilize R-508B. In addition, 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.degree. C. Further, in some embodiments, the
cascade cooling system 400 is implemented upstream of a nitrogen
refrigeration system or a methane autorefrigeration system.
[0077] Within the first refrigeration system 402, a vapor/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 stream is
separated in a first flash drum 414. A portion of the vapor/liquid
refrigerant stream 406 may be flowed directly into the first flash
drum 414 via a bypass valve 416.
[0078] 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 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 may be flowed back to the second
refrigeration system 404.
[0079] 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 chilling
system 454 may be, for example, performed by heat exchange with
various process streams, such as a natural gas stream coming from a
final flash drum that separates NGL from the gas.
[0080] 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 may be a level control valve for controlling fluid
entering flash drum 462.
[0081] 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.
[0082] 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 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.
[0083] 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.
[0084] FIG. 5 is process flow diagram of an expansion refrigeration
system 500 for hydrocarbon dew point control. Condensation of heavy
hydrocarbons, e.g., C.sub.3-C.sub.6, in natural gas within pipes
may result in liquid slugging on pipelines and disruption of gas
receiving facilities. Therefore, the hydrocarbon dew point may be
reduced using the expansion refrigeration system 500 in order to
prevent such condensation.
[0085] 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).
[0086] 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.
[0087] 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 heavy hydrocarbons
512 may then be flowed out of the expansion refrigeration system
500 through a second outlet valve 524.
[0088] 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.
[0089] In an embodiment, a cooling system, for example, using a
fluorocarbon refrigerant and a nitrogen refrigerant, may be used to
add further cooling to the process. This cooling may be implemented
by placing a heat exchanger 530 in the natural gas stream 508 or
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 C.sub.3s 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.
[0090] 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. For example, in some
embodiments, the expansion refrigeration system 500 is implemented
within a cascade cooling system including two fluorocarbon
refrigeration systems upstream of a nitrogen refrigeration system.
In such embodiments, the refrigerant liquid 532 that is flashed
across an expansion valve 534 and flowed through the chiller 530 is
a fluorocarbon refrigerant from one of the fluorocarbon
refrigeration systems or a nitrogen refrigerant from the nitrogen
refrigeration system.
[0091] FIG. 6 is a process flow diagram of an expansion
refrigeration system 600 for NGL production. 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.
[0092] 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, 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.
[0093] 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.
[0094] 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.
[0095] 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.
[0096] 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 638, such as a fluorocarbon refrigerant
or a nitrogen refrigerant. 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.
[0097] 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. 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.
[0098] 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. For example, in some
embodiments, the expansion refrigeration system 600 is implemented
within a cascade cooling system including two fluorocarbon
refrigeration systems upstream of a nitrogen refrigeration system.
In such embodiments, the refrigerant 638 that is utilized within
the heat exchanger 636 is a fluorocarbon refrigerant from one of
the fluorocarbon refrigeration systems or a nitrogen refrigerant
from the nitrogen refrigeration system.
[0099] FIG. 7 is a process flow diagram of a LNG production system
700. As shown in 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 system 708, the natural gas stream 704 may be purified
and cooled. For example, the natural gas stream 704 may be cooled
using a first fluorocarbon refrigerant 710, a second fluorocarbon
refrigerant 712, and a high-pressure nitrogen refrigerant 714. The
cooling of the natural gas stream 704 may result in the production
of the LNG 702.
[0100] Within the LNG production system 700, heavy hydrocarbons 716
may be removed from the natural gas stream 704, and a portion of
the heavy hydrocarbons 716 may be used to produce gasoline 718
within a heavy hydrocarbon processing system 720. In addition, any
residual natural gas 722 that is separated from the heavy
hydrocarbons 716 during the production of the gasoline 718 may be
returned to the natural gas stream 704.
[0101] The produced LNG 702 may include some amount of nitrogen
724. Therefore, the LNG 702 may be flowed through a NRU 726. The
NRU 726 separates the nitrogen 724 from the LNG 702, producing the
final LNG product.
[0102] 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 or different locations for the
fluorocarbon refrigerant chillers within the process, depending on
the details of the specific implementation. 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.
[0103] Systems for the Production of LNG
[0104] FIGS. 8A and 8B are process flow diagrams of a cascade
cooling system 800. The cascade cooling system 800 may be used for
the production of LNG, and may be implemented within a hydrocarbon
processing system. The cascade cooling system 800 may operate at
low temperatures, e.g., below about -18.degree. C., or below about
-29.degree. C., or below about -40.degree. C. In addition, the
cascade cooling system 800 may employ more than one refrigerant and
provide refrigeration at multiple temperatures.
[0105] The cascade cooling system 800 may include a first
fluorocarbon refrigeration system 802, as shown in FIG. 8A, which
may utilize a first fluorocarbon refrigerant, such as R-410A. The
cascade cooling system 800 may also include a second fluorocarbon
refrigeration system 804, as shown in FIG. 8B, which may utilize a
second fluorocarbon refrigerant, such as R-508B. In addition, the
cascade cooling system 800 may include a nitrogen refrigeration
system 806, as shown in FIG. 8B.
[0106] A natural gas stream 808 may be flowed through a chiller
810, which pre-cools the natural gas stream 808 via indirect heat
exchange with a cooling fluid. The natural gas stream 808 may then
be flowed into a pipe joint 812 within the cascade cooling system
800. The pipe joint 812 may be configured to split the natural gas
stream 808 into three separate natural gas streams. A first natural
gas stream may be flowed into the first fluorocarbon refrigeration
system 802 via line 814, while a second natural gas stream and a
third natural gas stream may be flowed into the system discussed
with respect to FIG. 9 via lines 816 and 818, respectively.
[0107] The natural gas stream may be flowed into the first
fluorocarbon refrigeration system 802 in preparation for cooling of
the natural gas stream. The natural gas stream may be cooled by
being passed through a series of heat exchangers 820, 822, and 824
within the first fluorocarbon refrigeration system 802. The heat
exchangers 820, 822, and 824 may also be referred to as
evaporators, chillers, or cold boxes. The natural gas stream may be
cooled within each of the heat exchangers 820, 822, and 824 through
indirect heat exchange with a circulating fluorocarbon refrigerant.
The fluorocarbon refrigerant may be a hydrofluorocarbon, such as
R-410A or R-404A, or any other suitable type of fluorocarbon
refrigerant.
[0108] The fluorocarbon refrigerant may be continuously circulated
through the first fluorocarbon refrigeration system 802, which may
continuously prepare the fluorocarbon refrigerant for entry into
each of the heat exchangers 820, 822, and 824. The fluorocarbon
refrigerant may exit the first heat exchanger 820 via line 826 as a
vapor fluorocarbon refrigerant. The vapor fluorocarbon refrigerant
can be combined with additional vapor fluorocarbon refrigerant
within two pipe joints 828 and 829. The vapor is then flowed
through a compressor 830 to increase the pressure of the vapor
fluorocarbon refrigerant, producing a superheated vapor
fluorocarbon refrigerant. The superheated vapor fluorocarbon
refrigerant is flowed through a condenser 832, which may cool and
condense the superheated vapor fluorocarbon refrigerant, producing
a liquid fluorocarbon refrigerant.
[0109] The liquid fluorocarbon refrigerant may be flowed through an
expansion valve 834, which lowers the temperature and pressure of
the liquid fluorocarbon refrigerant. This may result in the flash
evaporation of the liquid fluorocarbon refrigerant, producing a
mixture of the liquid fluorocarbon refrigerant and a vapor
fluorocarbon refrigerant. The liquid fluorocarbon refrigerant and
the vapor fluorocarbon refrigerant may be flowed into a first flash
drum 836 via line 838. Within the first flash drum 836, the liquid
fluorocarbon refrigerant may be separated from the vapor
fluorocarbon refrigerant.
[0110] The vapor fluorocarbon refrigerant may be flowed from the
first flash drum 836 to the pipe joint 828 via line 839. The liquid
fluorocarbon refrigerant may be flowed into a pipe joint 840, which
may split the liquid fluorocarbon refrigerant into two separate
liquid fluorocarbon refrigerant streams. One liquid fluorocarbon
refrigerant stream may be flowed through the first heat exchanger
820, partly or completely flashed to vapor, and returned to the
pipe joint 828 via line 826. The other liquid fluorocarbon
refrigerant stream may be flowed to a second flash drum 842 via
line 844. The line 844 may also include an expansion valve 846 that
throttles the liquid fluorocarbon refrigerant stream to control the
flow of the liquid fluorocarbon refrigerant stream into the second
flash drum 842. The throttling of the liquid fluorocarbon
refrigerant stream within the expansion valve 846 may result in the
flash evaporation of the liquid fluorocarbon refrigerant stream,
producing a mixture of both vapor and liquid fluorocarbon
refrigerant.
[0111] The second flash drum 842 may separate the vapor
fluorocarbon refrigerant from the liquid fluorocarbon refrigerant.
The vapor fluorocarbon refrigerant may be flowed into a pipe joint
848 via line 850. The pipe joint 848 may combine the vapor
fluorocarbon refrigerant with vapor fluorocarbon refrigerant
recovered from the second heat exchanger 822. The vapor
fluorocarbon refrigerant may then be flowed into another pipe joint
852. The pipe joint 852 may combine the vapor fluorocarbon
refrigerant with vapor fluorocarbon refrigerant recovered from the
third heat exchanger 824. The combined vapor fluorocarbon
refrigerant may be compressed within a compressor 854 and flowed
into the pipe joint 829 via line 856 to be combined with the vapor
from the flash drum 836 and the heat exchanger 820.
[0112] The liquid fluorocarbon refrigerant may be flowed from the
second flash drum 842 to a pipe joint 858, which may split the
liquid fluorocarbon refrigerant into two separate liquid
fluorocarbon refrigerant streams. One liquid fluorocarbon
refrigerant stream may be flowed through the second heat exchanger
822 and returned to the pipe joint 848 via line 860. The other
liquid fluorocarbon refrigerant stream may be flowed through the
third heat exchanger 824 via line 862. The line 862 may also
include an expansion valve 864 that allows the liquid fluorocarbon
refrigerant to flash, and, thus, lowers the pressure and
temperature, of the liquid fluorocarbon refrigerant stream as it
flows into the third heat exchanger 824. From the third heat
exchanger 824, the liquid fluorocarbon refrigerant stream may be
compressed within a compressor 866 and sent to the pipe joint 852
via line 868.
[0113] In various embodiments, a fluorocarbon refrigerant of the
second fluorocarbon refrigeration system 804 is precooled within
the first fluorocarbon refrigeration system 802. For example, the
fluorocarbon refrigerant of the second fluorocarbon refrigerant may
be precooled by being flowed through the first heat exchanger 820.
The fluorocarbon refrigerant may be a hydrofluorocarbon, such as
R-508B, or any other suitable type of fluorocarbon. The
fluorocarbon refrigerant may be flowed from the second fluorocarbon
refrigeration system 804 to the first heat exchanger 820 via line
870.
[0114] After the natural gas stream has been progressively chilled
within each of the heat exchangers 820, 822, and 824, it is flowed
into the second fluorocarbon refrigeration system 804, as shown in
FIG. 8B, via line 874. The second fluorocarbon refrigeration system
804 may include a fourth heat exchanger 876 and a fifth heat
exchanger 878, which may further cool the natural gas stream using
the fluorocarbon refrigerant.
[0115] The fluorocarbon refrigerant may be continuously circulated
through the second refrigeration system 804, which prepares the
fluorocarbon refrigerant for entry into each of the heat exchangers
876 and 878. The fluorocarbon refrigerant may exit the fourth heat
exchanger 876 as a vapor fluorocarbon refrigerant stream. The vapor
fluorocarbon refrigerant stream may be combined with another vapor
fluorocarbon refrigerant stream within a pipe joint 880, and may be
combined with yet another vapor fluorocarbon refrigerant stream
from the fifth heat exchanger 878 within another pipe joint 882.
The vapor fluorocarbon refrigerant stream may then be flowed
through a compressor 884, which may increase the pressure of the
vapor fluorocarbon refrigerant stream, producing a superheated
fluorocarbon refrigerant stream. The superheated fluorocarbon
refrigerant stream may be flowed through a pipe joint 886 and
another compressor 888, which may further increase the pressure of
the superheated fluorocarbon refrigerant stream.
[0116] The superheated fluorocarbon refrigerant stream may be
flowed through a gas cooler 890. The gas cooler 890 may cool the
superheated fluorocarbon refrigerant stream, producing a cool vapor
fluorocarbon refrigerant stream. In some cases, if the vapor
fluorocarbon refrigerant stream is below ambient temperature, the
vapor fluorocarbon refrigerant stream may not be flowed through the
gas cooler 890. The liquid fluorocarbon refrigerant stream may then
be flowed through the first heat exchanger 820 within the first
fluorocarbon refrigeration system 802 via the line 870.
[0117] Once the fluorocarbon refrigerant stream has passed through
the first heat exchanger 820, the fluorocarbon refrigerant stream
may enter a third flash drum 892 within the second fluorocarbon
refrigeration system 804 via line 894. Line 894 may include an
expansion valve 896 that controls the flow of the fluorocarbon
refrigerant stream into the third flash drum 892. The expansion
valve 896 may reduce the temperature and pressure of the
fluorocarbon refrigerant stream, resulting in the flash evaporation
of the fluorocarbon refrigerant stream into both a vapor
fluorocarbon refrigerant stream and a liquid fluorocarbon
refrigerant stream.
[0118] The vapor fluorocarbon refrigerant stream and the liquid
fluorocarbon refrigerant stream may be flashed into the third flash
drum 892, which may separate the vapor fluorocarbon refrigerant
stream from the liquid fluorocarbon refrigerant stream. The vapor
fluorocarbon refrigerant stream may be flowed into the pipe joint
886 via line 898. The liquid fluorocarbon refrigerant stream may be
flowed from the third flash drum 892 to a fourth flash drum 904 via
line 906. Line 906 may include an expansion valve 908 that controls
the flow of the fluorocarbon refrigerant stream into the fourth
flash drum 904. The expansion valve 908 may further reduce the
temperature and pressure of the fluorocarbon refrigerant stream,
resulting in the flash evaporation of the fluorocarbon refrigerant
stream into both a vapor fluorocarbon refrigerant stream and a
liquid fluorocarbon refrigerant stream.
[0119] The liquid fluorocarbon refrigerant stream may be flowed
from the fourth flash drum 904 to a pipe joint 910, which may split
the liquid fluorocarbon refrigerant stream into two separate liquid
fluorocarbon refrigerant streams. One liquid fluorocarbon
refrigerant stream may be flowed through the fourth heat exchanger
876 and returned to the pipe joint 880 via line 912. The other
liquid fluorocarbon refrigerant stream may be flowed through the
fifth heat exchanger 878 via line 914. Line 914 may also include an
expansion valve 916 that controls the flow of the liquid
fluorocarbon refrigerant stream into the fifth heat exchanger 878,
e.g., by allowing the fluorocarbon refrigerant stream to flash,
lowering the temperature and creating a vapor fluorocarbon
refrigerant stream and a liquid fluorocarbon refrigerant stream.
From the fifth heat exchanger 878, the resulting vapor fluorocarbon
refrigerant stream may be compressed within a compressor 918 and
then flowed into the pipe joint 882 to be recirculated.
[0120] After the natural gas stream has been cooled within the heat
exchangers 876 and 878 through indirect heat exchange with the
fluorocarbon refrigerant stream, the natural gas stream may be
flowed into the nitrogen refrigeration system 806 via line 920. In
various embodiments, a nitrogen refrigerant stream of the nitrogen
refrigeration system 806 is precooled by being flowed through each
of the heat exchangers 820, 822, 824, and 876. The nitrogen
refrigerant stream may be flowed from the nitrogen refrigeration
system 806 to the heat exchangers 820, 822, 824, and 876 via line
921.
[0121] Within the nitrogen refrigeration system 806, the natural
gas stream may be cooled within a sixth heat exchanger 922 via
indirect heat exchange with the nitrogen refrigerant stream. The
nitrogen refrigerant stream may be continuously circulated through
the nitrogen refrigeration system 806, which prepares the nitrogen
refrigerant stream for entry into the sixth heat exchanger 922. The
nitrogen refrigerant may be flowed through the sixth heat exchanger
922 as two separate nitrogen refrigerant streams. From the sixth
heat exchanger 922, the nitrogen refrigerant streams may be
combined within a pipe joint 924.
[0122] The combined nitrogen refrigerant stream may be flowed
through a seventh heat exchanger 926 via line 928. Within the
seventh heat exchanger 926, the nitrogen refrigerant stream may
provide cooling for a high pressure nitrogen refrigerant stream
that is flowing in the opposite direction. From the seventh heat
exchanger 926, the nitrogen refrigerant stream may be compressed
within a first compressor 930, cooled within a first chiller 932,
compressed within a second compressor 934, and cooled within a
second chiller 936. The resulting high pressure nitrogen
refrigerant stream may then be flowed into a pipe joint 938, which
may split the high pressure nitrogen refrigerant stream into two
separate high pressure nitrogen refrigerant streams.
[0123] From the pipe joint 938, one high pressure nitrogen
refrigerant stream may be flowed through the heat exchangers 820,
822, 824, and 876 via the line 921. Upon exiting the fourth heat
exchanger 876, the nitrogen refrigerant stream may be expanded
within an expander 940, generating power, and flowed through the
sixth heat exchanger 922 to provide cooling for the natural gas
stream.
[0124] The other high pressure nitrogen refrigerant stream may be
flowed from the pipe joint 938 through a third compressor 942, a
third chiller 944, and the seventh heat exchanger 926. The high
pressure nitrogen refrigerant stream may then be expanded within an
expander 946, generating power, and flowed through the sixth heat
exchanger 922 to provide cooling for the natural gas stream. The
power generated in expanders 940 and 946 may be used to generate
electricity or to drive all, some (or part) of the compressors 930,
934, or 942.
[0125] FIG. 9 is a process flow diagram of a system 900 including a
NRU 902. The system 900 may be located downstream of the cascade
cooling system 800, and may be implemented within the same
hydrocarbon processing system as the cascade cooling system
800.
[0126] Once the natural gas stream has been cooled within the
nitrogen refrigeration system 806, the natural gas stream may be in
the form of LNG. The LNG stream may be flowed into the system 900
via line 948. Specifically, the LNG stream may be flowed into a
pipe joint 950, which may combine the LNG stream from line 948 with
the natural gas stream from line 816. Initial cooling of the
natural gas stream from line 816 may be performed within an eighth
heat exchanger 952 prior to flowing the natural gas stream into the
pipe joint 950.
[0127] From the pipe joint 950, the LNG stream may be flowed into
the NRU 902 to remove excess nitrogen from the LNG stream.
Specifically, the LNG stream may be flowed into a reboiler 954,
which may decrease the temperature of the LNG stream. The cooled
LNG stream may be expanded within a hydraulic expansion turbine 956
and then flowed through an expansion valve 958, which lowers the
temperature and pressure of the LNG stream.
[0128] The LNG stream may be flowed into a cryogenic fractionation
column 960, such as an NRU tower, within the NRU 902. In addition,
heat may be transferred to the cryogenic fractionation column 960
from the reboiler 954 via line 962. The cryogenic fractionation
column 960 may separate nitrogen from the LNG stream via a
cryogenic distillation process. An overhead stream may be flowed
out of the cryogenic fractionation column 960 via line 964. The
overhead stream may include primarily methane, nitrogen, and other
low boiling point or non-condensable gases, such as helium, which
have been separated from the LNG stream.
[0129] In some embodiments, the overhead stream is flowed into an
overhead condenser (not shown), which may separate any liquid
within the overhead stream and return it to the cryogenic
fractionation column 960 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 through the eighth heat
exchanger 952 via line 964. Within the eighth heat exchanger 952,
the temperature of the vapor fuel stream may be increased via
indirect heat exchange with the natural gas stream, producing a
vapor fuel stream. The vapor fuel stream may be combined with other
vapor fuel streams within a pipe joint 966. The combined vapor fuel
stream may then be compressed and cooled within a series of
compressors 968, 970, and 972 and chillers 974, 976, 978. The
resulting vapor fuel stream may be combined with the natural gas
stream from line 818, which may be a vapor fuel stream from the
natural gas stream 808, within a pipe joint 980. The vapor fuel
stream may then be flowed out of the system 900 as fuel 982 via
line 984.
[0130] The bottoms stream that is produced within the cryogenic
fractionation column 960 includes primarily LNG with traces of
nitrogen. The LNG stream may be flowed into LNG tank 986 via line
988. The line 988 may include a valve 990 that is used to control
the flow of the LNG stream into the LNG tank 986. The LNG tank 986
may store the LNG stream for any period of time. Boil-off gas
generated within the LNG tank 986 may be flowed to the pipe joint
966 via line 992. At any point in time, the final LNG stream 994
may be transported to a LNG tanker 996 using a pump 998, for
transport to markets. Additional boil-off gas 999 generated while
loading the final LNG stream 944 into the LNG tanker 996 may be
recovered in the cascade cooling system 800.
[0131] It is to be understood that the process flow diagrams of
FIGS. 8A, 8B, and 9 are not intended to indicate that the cascade
cooling system 800 or the system 900 is to include all the
components shown in FIG. 8A, 8B, or 9. Further, the cascade cooling
system 800 or the system 900 may include any number of additional
components not shown in FIG. 8A, 8B, or 9, respectively, depending
on the details of the specific implementation. In various
embodiments, the heat exchangers 820, 822, 824, 876, 878, and 922
include high convection rate type tubes. The use of such high
convection rate type tubes may reduce the size of the equipment and
the inventory of refrigerant that is used to provide cooling within
the heat exchangers 820, 822, 824, 876, 878, and 922. In addition,
any of the heat exchangers 820, 822, 824, 876, 878, 922, or 926 may
be included within a spiral wound type unit or a brazed aluminum
type unit.
[0132] In various embodiments, the compressors 830, 854, 866, 888,
884, 918, 930, 934, 942, 968, 972, and 976 are centrifugal type
compressors. In order to reduce the loss of refrigerant to the
atmosphere, each compressor 830, 854, 866, 888, 884, 918, 930, 934,
942, 968, 972, and 976 may also include a reclaimer or a seal leak
gas recovery system.
[0133] FIGS. 10A and 10B are process flow diagrams of another
cascade cooling system 1000. The cascade cooling system 1000 may be
a modified version of the cascade cooling system 800 of FIGS. 8A
and 8B. Like numbered items are as described with respect to FIGS.
8A and 8B. The cascade cooling system 1000 may be implemented
within a hydrocarbon processing system.
[0134] The cascade cooling system 1000 may include a first
fluorocarbon refrigeration system 1002, as shown in FIG. 10A, which
may utilize a first fluorocarbon refrigerant, such as R-410A. The
cascade cooling system 1000 may also include a second fluorocarbon
refrigeration system 1004, as shown in FIG. 10B, which may utilize
a second fluorocarbon refrigerant, such as R-508B. In addition, the
cascade cooling system 1000 may include a nitrogen refrigeration
system 1006, as shown in FIG. 10B.
[0135] The first fluorocarbon refrigeration system 1002 of FIG. 10A
may be similar to the first fluorocarbon refrigeration system 802
of FIG. 8A. However, the first fluorocarbon refrigeration system
1002 of FIG. 10A may include a second heat exchanger 1008 and a
third heat exchanger 1010 in place of the heat exchangers 822 824
within the first fluorocarbon refrigeration system 802 of FIG.
8A.
[0136] Within the first fluorocarbon refrigeration system 1002, a
fluorocarbon refrigerant of the second fluorocarbon refrigeration
system 1004 is precooled, condensed, and sub-cooled by being flowed
through the heat exchangers 820, 1008, and 1010 respectively. The
fluorocarbon refrigerant may be a hydrofluorocarbon, such as
R-508B, or any other suitable type of fluorocarbon. The
fluorocarbon refrigerant may be flowed from the second fluorocarbon
refrigeration system 1004 to the heat exchangers 820, 1008, and
1010 within the first fluorocarbon refrigeration system 1002 via
line 870. Thus, the first fluorocarbon refrigeration system 1002 of
FIG. 10A may provide for a greater degree of precooling and less
compression of the second fluorocarbon refrigerant than the first
fluorocarbon refrigeration system 802 of FIG. 8A, since the
fluorocarbon refrigerant is flowed through all three heat
exchangers 802, 1008, and 1010.
[0137] The natural gas stream is progressively chilled within each
of the heat exchangers 820, 1008, and 1010. The chilled natural gas
stream is then flowed into the second fluorocarbon refrigeration
system 1004, as shown in FIG. 10B, via line 874. The second
fluorocarbon refrigeration system 1004 may include the fourth heat
exchanger 876 and a fifth heat exchanger 1012, which may further
cool the natural gas stream using the fluorocarbon refrigerant.
[0138] The fluorocarbon refrigerant may be continuously circulated
through the second refrigeration system 1004, which prepares the
fluorocarbon refrigerant for entry into each of the heat exchangers
876 and 1012. The fluorocarbon refrigerant may exit the fourth heat
exchanger 876 as a vapor fluorocarbon refrigerant stream. The vapor
fluorocarbon refrigerant stream may be combined with another vapor
fluorocarbon refrigerant stream within the pipe joint 880, and may
be combined with another vapor fluorocarbon refrigerant stream from
the fifth heat exchanger 1012 within the pipe joint 882. The vapor
fluorocarbon refrigerant stream may then be flowed through a
compressor 884, which may increase the pressure of the vapor
fluorocarbon refrigerant stream. The vapor may then be flowed
through the first heat exchanger 820 within the first fluorocarbon
refrigeration system 1002 via the line 870.
[0139] Once the fluorocarbon refrigerant stream has passed through
the heat exchangers 820, 1008, and 1010, the fluorocarbon
refrigerant stream may enter a third flash drum 1013 within the
second fluorocarbon refrigeration system 1004 via line 1014. Line
1014 may include the expansion valve 908, which controls the flow
of the fluorocarbon refrigerant stream into the third flash drum
1013. The expansion valve 908 may reduce the temperature and
pressure of the fluorocarbon refrigerant stream, resulting in the
flash evaporation of the fluorocarbon refrigerant stream into both
a vapor fluorocarbon refrigerant stream and a liquid fluorocarbon
refrigerant stream.
[0140] The vapor fluorocarbon refrigerant stream and the liquid
fluorocarbon refrigerant stream may be flashed into the third flash
drum 1013, which may separate the vapor fluorocarbon refrigerant
stream from the liquid fluorocarbon refrigerant stream. The vapor
fluorocarbon refrigerant stream may be flowed into the pipe joint
880 via line 1016. The liquid fluorocarbon refrigerant stream may
be flowed from the third flash drum 1013 to the pipe joint 910,
which may split the liquid fluorocarbon refrigerant stream into two
separate liquid fluorocarbon refrigerant streams. One liquid
fluorocarbon refrigerant stream may be flowed through the fourth
heat exchanger 876 and returned to the pipe joint 880 via line 912.
The other liquid fluorocarbon refrigerant stream may be flowed
through the fifth heat exchanger 1012 via line 914. Line 914 may
also include an expansion valve 916 that controls the flow of the
liquid fluorocarbon refrigerant stream into the fifth heat
exchanger 1012, e.g., by allowing the fluorocarbon refrigerant
stream to flash, lowering the temperature and creating a vapor
fluorocarbon refrigerant stream and a liquid fluorocarbon
refrigerant stream. From the fifth heat exchanger 1012, the
resulting vapor fluorocarbon refrigerant stream may be compressed
within the compressor 918 and then flowed into the pipe joint 882
to be recirculated.
[0141] After the natural gas stream has been cooled within the heat
exchangers 876 and 878 through indirect heat exchange with the
fluorocarbon refrigerant stream, the natural gas stream may be
flowed into the nitrogen refrigeration system 1006 via line 920. In
various embodiments, a nitrogen refrigerant stream of the nitrogen
refrigeration system 1006 is precooled by being flowed through each
of the heat exchangers 820, 1008, 1010, 876, and 1012. The nitrogen
refrigerant stream may be flowed from the nitrogen refrigeration
system 1006 to the heat exchangers 820, 1008, 1010, 876, and 1012
via line 921.
[0142] Within the nitrogen refrigeration system 1006, the natural
gas stream may be cooled within a sixth heat exchanger 1018 via
indirect heat exchange with the nitrogen refrigerant stream. The
nitrogen refrigerant stream may be continuously circulated through
the nitrogen refrigeration system 1006, which prepares the nitrogen
refrigerant stream for entry into the sixth heat exchanger
1018.
[0143] From the sixth heat exchanger 1018, the nitrogen refrigerant
stream may be combined with another nitrogen refrigerant stream
within a pipe joint 1020. The combined nitrogen refrigerant stream
may be flowed through the seventh heat exchanger 926 via line 928.
Within the seventh heat exchanger 926, the nitrogen refrigerant
stream may provide cooling for a high pressure nitrogen refrigerant
stream that is flowing in the opposite direction. From the seventh
heat exchanger 926, the nitrogen refrigerant stream may be
compressed within the first compressor 930, cooled within the first
chiller 932, compressed within the second compressor 934, cooled
within the second chiller 936, compressed within a third compressor
1022, and cooled within a third chiller 1024. The resulting high
pressure nitrogen refrigerant stream may then be flowed into a pipe
joint 1026, which may split the high pressure nitrogen refrigerant
stream into two separate high pressure nitrogen refrigerant
streams.
[0144] From the pipe joint 1026, one high pressure nitrogen
refrigerant stream may be flowed through the heat exchangers 820,
1008, 1010, 876, and 1012 via the line 921. Upon exiting the fifth
heat exchanger 1012, the nitrogen refrigerant stream may be
expanded within an expander 1028, generating power, and flowed into
the pipe joint 1020 to be combined with the nitrogen refrigerant
stream exiting the sixth heat exchanger 1018.
[0145] The other high pressure nitrogen refrigerant stream may be
flowed from the pipe joint 1026 through the seventh heat exchanger
926. The high pressure nitrogen refrigerant stream may then be
expanded within an expander 1030, generating power, and flowed
through the sixth heat exchanger 1018 to provide cooling for the
natural gas stream. The power generated in expanders 1028 and 1030
may be used to generate electricity or to drive part of the
compressors 930, 934 or 1022.
[0146] Once the natural gas stream has been cooled within the
nitrogen refrigeration system 1006, the natural gas stream may be
in the form of LNG. The LNG stream may be flowed into the system
900 of FIG. 9 via line 948. Within the system 900, nitrogen may be
removed from the LNG within the NRU 902, and the final LNG stream
994 may be obtained, as discussed with respect to FIG. 9.
[0147] FIG. 10C is a process flow diagram of an alternative
embodiment of the cascade cooling system 1000 with a simplified
nitrogen refrigeration system 1032. As shown in FIG. 10C, the pipe
joints 1020 and 1026, the seventh heat exchanger 926, the expander
1030, and the chillers 932 and 936 are not included within the
nitrogen refrigeration system 1032. In addition, the first
compressor 930 and the second compressor 934 are combined into a
single unit, i.e., compressor 1134. In such embodiments, the entire
nitrogen refrigerant stream is flowed through the heat exchangers
820, 1008, 1010, 876, and 1012 via the line 921. Thus, such an
embodiment simplifies the design of the cascade cooling system
1000. The power generated in expander 1028 may be used to generate
electricity or to drive part of the compressors 1022 or 1134.
[0148] It is to be understood that the process flow diagrams of
FIGS. 10A, 10B, and 10C are not intended to indicate that the
cascade cooling system 1000 is to include all the components shown
in FIGS. 10A, 10B, and 10C. Further, the cascade cooling system
1000 may include any number of additional components not shown in
FIGS. 10A, 10B, and 10C, depending on the details of the specific
implementation.
[0149] FIGS. 11A and 11B are process flow diagrams of another
cascade cooling system 1100. The cascade cooling system 1100 may be
a modified version of the cascade cooling systems 800 and 1000 of
FIGS. 8A, 8B, 10A, 10B, and 10C, respectively. Like numbered items
are as described with respect to FIGS. 8A, 8B, 10A, 10B, and 10C.
The cascade cooling system 1100 may be implemented within a
hydrocarbon processing system.
[0150] The cascade cooling system 1100 may include a first
fluorocarbon refrigeration system 1102, as shown in FIG. 11A, which
may utilize a first fluorocarbon refrigerant, such as R-410A. The
cascade cooling system 1100 may also include a second fluorocarbon
refrigeration system 1104, as shown in FIG. 11B, which may utilize
a second fluorocarbon refrigerant, such as R-508B.
[0151] FIG. 11C is a process flow diagram of an autorefrigeration
system 1105 that is implemented within the same hydrocarbon
processing system as the cascade cooling system 1100 of FIGS. 11A
and 11B. Like numbered items are as described with respect to FIGS.
8A, 8B, 9, 10A, 10B, 10C, 11A, and 11B. The autorefrigeration
system 1105 may be used to produce LNG from the natural gas stream.
In addition, the autorefrigeration system 1105 may include a NRU
1106 for removing nitrogen from the natural gas stream.
[0152] A natural gas stream 808 may be flowed through the chiller
810, which pre-cools the natural gas stream 808 via indirect heat
exchange with a cooling fluid. The natural gas stream 808 may then
be flowed into the pipe joint 812 within the cascade cooling system
1100. The pipe joint 812 may be configured to split the natural gas
stream 808 into three separate natural gas streams. A first natural
gas stream may be flowed into a pipe joint 1107 via line 814, while
a second natural gas stream and a third natural gas stream may be
flowed into the autorefrigeration system 1105 via lines 816 and
818, respectively.
[0153] Within the pipe joint 1107, the natural gas stream may be
combined with a methane recycle stream that is returned from the
autorefrigeration system 1105 via line 1108. The combined natural
gas stream may then be flowed into the first fluorocarbon
refrigeration system 1102 in preparation for cooling of the natural
gas stream. The natural gas stream may be cooled by being passed
through a series of heat exchangers 1110, 822, and 824 within the
first fluorocarbon refrigeration system 1102. The natural gas
stream may be cooled within each of the heat exchangers 1110, 822,
and 824 through indirect heat exchange with a circulating
fluorocarbon refrigerant, as discussed with respect to FIG. 8A.
[0154] The cooled natural gas stream is then flowed into the second
fluorocarbon refrigeration system 1104, as shown in FIG. 11B, via
line 874. The second fluorocarbon refrigeration system 1104 may
include a fourth heat exchanger 1112 and a fifth heat exchanger
1114, which may further cool the natural gas stream using the
fluorocarbon refrigerant.
[0155] The fluorocarbon refrigerant may be continuously circulated
through the second refrigeration system 1104, which prepares the
fluorocarbon refrigerant for entry into each of the heat exchangers
1112 and 1114. The fluorocarbon refrigerant may exit the fourth
heat exchanger 1112 as a vapor fluorocarbon refrigerant stream. The
vapor fluorocarbon refrigerant stream may be combined with another
vapor fluorocarbon refrigerant stream within the pipe joint 880,
and may be combined with another vapor fluorocarbon refrigerant
stream from the fifth heat exchanger 1114 within the pipe joint
882. The vapor fluorocarbon refrigerant stream may then be flowed
through a compressor 884, which may increase the pressure of the
vapor fluorocarbon refrigerant stream. The vapor may then be flowed
through the first heat exchanger 1110 within the first fluorocarbon
refrigeration system 1102 via the line 870.
[0156] Once the fluorocarbon refrigerant stream has passed through
the heat exchangers 1110, 822, and 824, the fluorocarbon
refrigerant stream may enter the third flash drum 1013 within the
second fluorocarbon refrigeration system 1104 via line 1014. Line
1014 may include the expansion valve 908, which controls the flow
of the fluorocarbon refrigerant stream into the third flash drum
1013. The expansion valve 908 may reduce the temperature and
pressure of the fluorocarbon refrigerant stream, resulting in the
flash evaporation of the fluorocarbon refrigerant stream into both
a vapor fluorocarbon refrigerant stream and a liquid fluorocarbon
refrigerant stream.
[0157] The vapor fluorocarbon refrigerant stream and the liquid
fluorocarbon refrigerant stream may be flashed into the third flash
drum 1013, which may separate the vapor fluorocarbon refrigerant
stream from the liquid fluorocarbon refrigerant stream. The vapor
fluorocarbon refrigerant stream may be flowed into the pipe joint
880 via line 1016. The liquid fluorocarbon refrigerant stream may
be flowed from the third flash drum 1013 to the pipe joint 910,
which may split the liquid fluorocarbon refrigerant stream into two
separate liquid fluorocarbon refrigerant streams. One liquid
fluorocarbon refrigerant stream may be flowed through the fourth
heat exchanger 1112 and returned to the pipe joint 880 via line
912. The other liquid fluorocarbon refrigerant stream may be flowed
through the fifth heat exchanger 1114 via line 914. Line 914 may
also include an expansion valve 916 that controls the flow of the
liquid fluorocarbon refrigerant stream into the fifth heat
exchanger 1114, e.g., by allowing the fluorocarbon refrigerant
stream to flash, lowering the temperature and creating a vapor
fluorocarbon refrigerant stream and a liquid fluorocarbon
refrigerant stream. From the fifth heat exchanger 1114, the
resulting vapor fluorocarbon refrigerant stream may be compressed
within the compressor 918 and then flowed into the pipe joint 882
to be recirculated.
[0158] After the natural gas stream has been cooled within the heat
exchangers 1112 and 1114 through indirect heat exchange with the
fluorocarbon refrigerant stream, the natural gas stream may be
flowed into the autorefrigeration system 1105 via line 1116. More
specifically, the natural gas stream may be flowed into a sixth
heat exchanger 1118 within the autorefrigeration system 1105.
Within the sixth heat exchanger 1118, the natural gas stream may be
cooled via indirect heat exchange with a lower temperature natural
gas stream flowing in the opposite direction.
[0159] From the sixth heat exchanger 1118, the natural gas stream
may be flowed into a pipe joint 1120, which splits the natural gas
stream into two separate natural gas streams. One natural gas
stream may be flowed through an expansion valve 1122, which may
lower the temperature and pressure of the natural gas stream. The
low temperature natural gas stream may then be flowed into the
sixth heat exchanger 1118 via line 1124, and may be used for
cooling of the natural gas stream within the sixth heat exchanger
1118. From the sixth heat exchanger 1118, the natural gas stream
may be flowed into a pipe joint 1126, in which it may be combined
with another natural gas stream. The combined natural gas stream
may be compressed within a compressor 1128 and then flowed into the
pipe joint 1107 within the first fluorocarbon refrigeration system
1102.
[0160] From the pipe joint 1120, the other natural gas stream may
be flowed into an additional pipe joint 1130, in which it may be
combined with another natural gas stream. The combined natural gas
stream may be flowed into the NRU 1106 to remove excess nitrogen
from the natural gas stream. Specifically, the natural gas stream
may be flowed into the reboiler 954, which may decrease the
temperature of the natural gas stream. The cooled natural gas
stream may be expanded within the hydraulic expansion turbine 986
and then flowed through expansion valve 988, which lowers the
temperature and pressure of the natural gas stream.
[0161] The natural gas stream may be flowed into the cryogenic
fractionation column 960 within the NRU 1106. In addition, heat may
be transferred to the cryogenic fractionation column 960 from the
reboiler 954 via line 962. The cryogenic fractionation column 960
may separate nitrogen from the natural gas stream via a cryogenic
distillation process. An overhead stream may be flowed out of the
cryogenic fractionation column 960 via line 964. The overhead
stream may include primarily methane, nitrogen, and other low
boiling point or non-condensable gases, such as helium, which have
been separated from the natural gas stream.
[0162] In some embodiments, the overhead stream is flowed into an
overhead condenser 1132, which may separate any liquid within the
overhead stream and return it to the cryogenic fractionation column
960 as reflux via line 1134. 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 through a seventh heat exchanger 1136
via line 964. Within the seventh heat exchanger 1136, the
temperature of the vapor fuel stream may be increased via indirect
heat exchange with the natural gas stream from line 816, producing
a vapor fuel stream. The vapor fuel stream may be compressed and
chilled within a series of compressors 1138 and 1140 and chillers
1142 and 1144. The resulting vapor fuel stream may be combined with
the natural gas stream from line 818, which may be a vapor fuel
stream from the natural gas stream 808, within the pipe joint 980.
The vapor fuel stream may then be flowed out of the
autorefrigeration system 1105 as fuel 982 via line 984.
[0163] The bottoms stream that is produced within the cryogenic
fractionation column 960 includes primarily LNG with traces of
nitrogen. The bottoms stream may be flowed through the overhead
condenser 1132 via line 1146. Line 1146 may also include an
expansion valve 1148 that controls the flow of the bottoms stream
into the overhead condenser 1132. The bottoms stream may be used as
refrigerant for the overhead condenser 1132.
[0164] From the overhead condenser 1132, the resulting mixed phase
stream may be flowed into a first flash drum 1150 via line 1152.
The first flash drum 1150 may separate the mixed phase stream into
a vapor stream that includes primarily natural gas and a LNG
stream. The vapor stream may be flowed into a pipe joint 1154. The
pipe joint 1154 may combine the vapor stream with another vapor
stream recovered from a second flash drum 1156. The combined vapor
streams may be flowed into a compressor 1158 via line 1160. From
the compressor 1158, the natural gas stream may be flowed into the
pipe joint 1126.
[0165] From the first flash drum 1150, the LNG stream may be flowed
into the second flash drum 1156 via line 1162. The line 1162 may
include an expansion valve 1164 that controls the flow of the LNG
stream into the second flash drum 1156, allowing a portion of the
liquid from the LNG stream to flash, creating a mixed phase system
that is flowed into the second flash drum 1156.
[0166] The second flash drum 1156 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 1166 via line 1168.
The pipe joint 1166 may combine the vapor stream with another vapor
stream recovered from a third flash drum 1170. The combined vapor
streams may be compressed within a compressor 1172 and flowed into
the pipe joint 1154.
[0167] The LNG stream may then be flowed into the third flash drum
1170 via line 1174. The line 1174 may include an expansion valve
1176 that controls the flow of the LNG stream into the third flash
drum 1170, allowing a portion of the liquid from the LNG to flash.
The third flash drum 1170 may further reduce the temperature and
pressure of the LNG stream such that the LNG stream approaches an
equilibrium temperature and pressure. The produced vapor stream may
be flowed into a pipe joint 1178, which may combine the vapor
stream with boil-off gas recovered from a LNG tank 1180. The
combined vapor streams may be compressed within a compressor 1182
and flowed into the pipe joint 1166.
[0168] The LNG stream may be flowed into a LNG tank 1180 via line
1184. The LNG tank 1180 may store the LNG stream for any period of
time. Boil-off gas generated within the LNG tank 1180 may be flowed
to the pipe joint 1178 via line 1186. At any point in time, the
final LNG stream 994 may be transported to a LNG tanker 996 using a
pump 998, for transport to markets. Additional boil-off gas 999
generated while loading the final LNG stream 944 into the LNG
tanker 996 may be recovered in the cascade cooling system 1100.
[0169] It is to be understood that the process flow diagrams of
FIGS. 11A, 11B, and 912 are not intended to indicate that the
cascade cooling system 1100 or the autorefrigeration system 1105 is
to include all the components shown in FIG. 11A, 11B, or 11C.
Further, the cascade cooling system 1100 or the autorefrigeration
system 1105 may include any number of additional components not
shown in FIG. 11A, 11B, or 11C, respectively, depending on the
details of the specific implementation.
[0170] The pressures of the refrigerant streams within the cascade
cooling systems 800, 1000, and 1100 of FIGS. 8A and 8B; 10A, 10B,
and 10C; 11A, and 11B, respectively, may vary considerably. In some
embodiments, the lowest refrigerant pressure is slightly above the
local atmospheric pressure, but may be at a vacuum. In other
embodiments, the lowest refrigerant pressure is between around 7-9
psia. This lowers the refrigerant temperature, increasing the load
on the fluorocarbon refrigeration systems, but reducing the load on
the nitrogen refrigeration system or methane autorefrigeration
system. In some embodiments, using sub-atmospheric pressures allows
refrigerant power to be shifted between the different fluorocarbon
refrigeration systems, allowing for load balancing and the use of
more operable drivers. For example, in some cases, refrigerant
drivers may be identical for all the fluorocarbon refrigeration
systems and the nitrogen refrigeration system.
[0171] Method for LNG Formation
[0172] FIG. 12 is a process flow diagram of a method 1200 for the
formation of LNG from a natural gas stream. The method 1200 may be
implemented within any suitable type of hydrocarbon processing
system. The method 1200 begins at block 1202, at which the natural
gas stream is cooled in a first fluorocarbon refrigeration system.
The first fluorocarbon refrigeration system may be a mechanical
refrigeration system, valve expansion system, turbine expansion
system, or the like. The first fluorocarbon refrigeration system
uses a first fluorocarbon refrigerant to cool the natural gas
stream. The first fluorocarbon refrigerant may be, for example, a
hydrofluorocarbon refrigerant, such as R-410A, or any other
suitable type of fluorocarbon refrigerant.
[0173] In various embodiments, the first fluorocarbon refrigerant
is compressed to provide a compressed first fluorocarbon
refrigerant, and the compressed first fluorocarbon refrigerant is
cooled by indirect heat exchange with a cooling fluid. The
compressed first fluorocarbon refrigerant may be expanded to cool
the compressed first fluorocarbon refrigerant, thereby producing an
expanded, cooled first fluorocarbon refrigerant. The expanded,
cooled first fluorocarbon refrigerant may be passed to a heat
exchange area, which may be any suitable type of heat exchanger,
such as a chiller or evaporator. In addition, the natural gas
stream may be compressed and cooled by indirect heat exchange with
an external cooling fluid. The natural gas stream may then be
chilled within the heat exchange area using the expanded, cooled
first fluorocarbon refrigerant.
[0174] The first fluorocarbon refrigeration system may also include
any number of additional refrigeration stages for cooling the
natural gas stream. For example, the first fluorocarbon
refrigeration system may be a three stage refrigeration system that
includes three heat exchange areas for cooling the natural gas
stream via indirect heat exchange with the first fluorocarbon
refrigerant.
[0175] At block 1204, the natural gas stream is cooled in a second
fluorocarbon refrigeration system. The second fluorocarbon
refrigeration system may be a mechanical refrigeration system,
valve expansion system, turbine expansion system, or the like. The
second fluorocarbon refrigeration system uses a second fluorocarbon
refrigerant to cool the natural gas stream. The second fluorocarbon
refrigerant may be, for example, a hydrofluorocarbon refrigerant,
such as R-508B, or any other suitable type of fluorocarbon
refrigerant.
[0176] In various embodiments, the second fluorocarbon refrigerant
is compressed to provide a compressed second fluorocarbon
refrigerant, and the compressed second fluorocarbon refrigerant is
cooled by indirect heat exchange with a cooling fluid. The
compressed second fluorocarbon refrigerant may be expanded to cool
the compressed second fluorocarbon refrigerant, thereby producing
an expanded, cooled second fluorocarbon refrigerant. The expanded,
cooled second fluorocarbon refrigerant may be passed to a heat
exchange area, which may be any suitable type of heat exchanger,
such as a chiller or evaporator. In addition, the natural gas
stream may be compressed and cooled by indirect heat exchange with
an external cooling fluid. The natural gas stream may then be
chilled within the heat exchange area using the expanded, cooled
second fluorocarbon refrigerant.
[0177] The second fluorocarbon refrigeration system may also
include any number of additional refrigeration stages for cooling
the natural gas stream. For example, the second fluorocarbon
refrigeration system may be a two stage refrigeration system that
includes two heat exchange areas for cooling the natural gas stream
via indirect heat exchange with the second fluorocarbon
refrigerant. In addition, the second fluorocarbon refrigerant may
be precooled within the first fluorocarbon refrigeration system.
This may be accomplished by flowing the second fluorocarbon
refrigerant through the heat exchange areas within the first
fluorocarbon refrigeration system, for example.
[0178] At block 1206, the natural gas stream is liquefied to form
LNG in a nitrogen refrigeration system. A nitrogen refrigerant may
be used to liquefy the natural gas stream within the nitrogen
refrigeration system. The nitrogen refrigerant may be maintained in
a gas phase within the nitrogen refrigeration system. In various
embodiments, the nitrogen is compressed and cooled in a series of
compressors and chillers, expanded within a hydraulic expansion
turbine to generate power and reduce the temperature of the
nitrogen refrigerant, and flowed through a heat exchanger. Within
the heat exchanger, the nitrogen refrigerant may liquefy the
natural gas stream to produce LNG via indirect heat exchange with
the natural gas stream.
[0179] At block 1208, nitrogen is removed from the LNG in a NRU.
The NRU may include a cryogenic fractionation column, such as a NRU
tower. Nitrogen that is separated from the LNG may be flowed out of
the cryogenic fractionation column as an overhead stream, while the
LNG may be flowed out of the cryogenic fractionation column as a
bottoms stream. In addition, a liquid feed from the bottom of the
nitrogen rejection unit may be used to provide cooling to a reflux
condenser at the top of the nitrogen rejection unit.
[0180] 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.
[0181] FIG. 13 is a process flow diagram of another method 1300 for
the formation of LNG from a natural gas stream. Like numbered items
are as described with respect to FIG. 12. The method 1300 may be
implemented within any suitable type of hydrocarbon processing
system. The method 1300 includes cooling a natural gas stream in a
first fluorocarbon refrigeration system at block 1202, and cooling
the natural gas stream in a second fluorocarbon refrigeration
system at block 1204.
[0182] In addition, at block 1302, the natural gas stream is cooled
to form LNG in a methane autorefrigeration system. The methane
autorefrigeration system may include a number of expansion valves
and flash drums for cooling the natural gas. In some embodiments,
the methane autorefrigeration system is the autorefrigeration
system 1105 discussed with respect to FIG. 11C. Further, in some
embodiments, a nitrogen rejection unit is located upstream of the
methane autorefrigeration system.
[0183] It is to be understood that the process flow diagram of FIG.
13 is not intended to indicate that the steps of the method 1300
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 1300, depending
on the details of the specific implementation.
Embodiments
[0184] Embodiments of the invention may include any combinations of
the methods and systems shown in the following numbered paragraphs.
This is not to be considered a complete listing of all possible
embodiments, as any number of variations can be envisioned from the
description herein.
[0185] 1. A hydrocarbon processing system for formation of a
liquefied natural gas (LNG), including: [0186] a first fluorocarbon
refrigeration system configured to chill a natural gas using a
first fluorocarbon refrigerant; [0187] a second fluorocarbon
refrigeration system configured to further chill the natural gas
using a second fluorocarbon refrigerant; [0188] a nitrogen
refrigeration system configured to cool the natural gas using a
nitrogen refrigerant to produce LNG; and [0189] a nitrogen
rejection unit configured to remove nitrogen from the LNG.
[0190] 2. The hydrocarbon processing system of paragraph 1, wherein
the first fluorocarbon refrigeration system is configured to cool
the second fluorocarbon refrigerant of the second fluorocarbon
refrigeration system.
[0191] 3. The hydrocarbon processing system of any of paragraphs 1
or 2, wherein the first fluorocarbon refrigeration system or the
second fluorocarbon refrigeration system, or both, is configured to
cool the nitrogen refrigerant of the nitrogen refrigeration
system.
[0192] 4. The hydrocarbon processing system of any of paragraphs
1-3, wherein the first fluorocarbon refrigeration system or the
second fluorocarbon refrigeration system, or both, includes
multiple cooling cycles.
[0193] 5. The hydrocarbon processing system of any of paragraphs
1-4, wherein the nitrogen refrigeration system includes a number of
heat exchangers configured to allow for cooling of the natural gas
via an indirect exchange of heat between the natural gas and the
nitrogen refrigerant.
[0194] 6. The hydrocarbon processing system of any of paragraphs
1-5, wherein the first fluorocarbon refrigeration system includes:
[0195] a compressor configured to compress the first fluorocarbon
refrigerant to provide a compressed first fluorocarbon refrigerant;
[0196] a chiller configured to cool the compressed first
fluorocarbon refrigerant by indirect heat exchange with a cooling
fluid; [0197] a valve configured to expand the compressed first
fluorocarbon refrigerant to cool the compressed first fluorocarbon
refrigerant, thereby producing a cooled first fluorocarbon
refrigerant; and [0198] a heat exchanger configured to cool the
natural gas via indirect heat exchange with the cooled first
fluorocarbon refrigerant.
[0199] 7. The hydrocarbon processing system of any of paragraphs
1-6, wherein the second fluorocarbon refrigeration system includes:
[0200] a compressor configured to compress the second fluorocarbon
refrigerant to provide a compressed second fluorocarbon
refrigerant; [0201] a chiller configured to cool the compressed
second fluorocarbon refrigerant by indirect heat exchange with a
cooling fluid; [0202] a valve configured to expand the compressed
second fluorocarbon refrigerant to cool the compressed second
fluorocarbon refrigerant, thereby producing a cooled second
fluorocarbon refrigerant; and [0203] a heat exchanger configured to
cool the natural gas via indirect heat exchange with the cooled
second fluorocarbon refrigerant.
[0204] 8. The hydrocarbon processing system of any of paragraphs
1-7, wherein the first fluorocarbon refrigerant includes
R-410A.
[0205] 9. The hydrocarbon processing system of any of paragraphs
1-8, wherein the second fluorocarbon refrigerant includes
R-508B.
[0206] 10. The hydrocarbon processing system of any of paragraphs
1-9, wherein the first fluorocarbon refrigerant or the second
fluorocarbon refrigerant, or both, includes a nontoxic,
nonflammable refrigerant.
[0207] 11. The hydrocarbon processing system of any of paragraphs
1-10, wherein the first fluorocarbon refrigeration system or the
second fluorocarbon refrigeration system, or both, includes two or
more chillers and two or more compressors.
[0208] 12. The hydrocarbon processing system of any of paragraphs
1-11, wherein the first fluorocarbon refrigeration system and the
second fluorocarbon refrigeration system are implemented in
series.
[0209] 13. The hydrocarbon processing system of any of paragraphs
1-12, wherein the nitrogen refrigerant is in a gas phase.
[0210] 14. The hydrocarbon processing system of any of paragraphs
1-13, wherein the nitrogen refrigeration system includes two or
more chillers, two or more expanders, and two or more
compressors.
[0211] 15. The hydrocarbon processing system of any of paragraphs
1-14, wherein the hydrocarbon processing system is configured to
chill the natural gas for hydrocarbon dew point control.
[0212] 16. The hydrocarbon processing system of any of paragraphs
1-15, wherein the hydrocarbon processing system is configured to
chill the natural gas for natural gas liquid extraction.
[0213] 17. The hydrocarbon processing system of any of paragraphs
1-16, wherein the hydrocarbon processing system is configured to
separate methane and lighter gases from carbon dioxide and heavier
gases.
[0214] 18. The hydrocarbon processing system of any of paragraphs
1-17, wherein the hydrocarbon processing system is configured to
prepare hydrocarbons for liquefied petroleum gas production
storage.
[0215] 19. The hydrocarbon processing system of any of paragraphs
1-18, wherein the hydrocarbon processing system is configured to
condense a reflux stream.
[0216] 20. A method for formation of a liquefied natural gas (LNG),
including: [0217] cooling a natural gas in a first fluorocarbon
refrigeration system; [0218] cooling the natural gas in a second
fluorocarbon refrigeration system; [0219] liquefying the natural
gas to form LNG in a nitrogen refrigeration system; and removing
nitrogen from the LNG in a nitrogen rejection unit.
[0220] 21. The method of paragraph 20, including cooling a second
fluorocarbon refrigerant of the second fluorocarbon refrigeration
system within the first fluorocarbon refrigeration system.
[0221] 22. The method of any of paragraphs 20 or 21, including
cooling a nitrogen refrigerant of the nitrogen refrigeration system
within the first fluorocarbon refrigeration system or the second
fluorocarbon refrigeration system, or both.
[0222] 23. The method of any of paragraphs 20-22, wherein cooling
the natural gas in the first fluorocarbon refrigeration system
includes: [0223] compressing a first fluorocarbon refrigerant to
provide a compressed first fluorocarbon refrigerant; [0224]
optionally cooling the compressed first fluorocarbon refrigerant by
indirect heat exchange with a cooling fluid; [0225] expanding the
compressed first fluorocarbon refrigerant to cool the compressed
first fluorocarbon refrigerant, thereby producing an expanded,
cooled first fluorocarbon refrigerant; [0226] passing said
expanded, cooled first fluorocarbon refrigerant to a first heat
exchange area; [0227] optionally compressing the natural gas;
[0228] optionally cooling the natural gas by indirect heat exchange
with an external cooling fluid; and [0229] heat exchanging the
natural gas with the expanded, cooled first fluorocarbon
refrigerant.
[0230] 24. The method of any of paragraphs 20-23, wherein cooling
the natural gas in the second fluorocarbon refrigeration system
includes: [0231] compressing a second fluorocarbon refrigerant to
provide a compressed second fluorocarbon refrigerant; [0232]
optionally cooling the compressed second fluorocarbon refrigerant
by indirect heat exchange with a cooling fluid; [0233] expanding
the compressed second fluorocarbon refrigerant to cool the
compressed second fluorocarbon refrigerant, thereby producing an
expanded, cooled second fluorocarbon refrigerant; [0234] passing
said expanded, cooled second fluorocarbon refrigerant to a first
heat exchange area; [0235] optionally compressing the natural gas;
[0236] optionally cooling the natural gas by indirect heat exchange
with an external cooling fluid; and [0237] heat exchanging the
natural gas with the expanded, cooled second fluorocarbon
refrigerant.
[0238] 25. The method of any of paragraphs 20-24, including
maintaining a nitrogen refrigerant of the nitrogen refrigeration
system in a gas phase using one or more expansion turbines.
[0239] 26. The method of any of paragraphs 20-25, including
chilling the natural gas in the first fluorocarbon refrigeration
system or the second fluorocarbon refrigeration system, or both,
using two or more refrigeration stages.
[0240] 27. The method of any of paragraphs 20-26, including
liquefying the natural gas in the nitrogen refrigeration system
using one or more refrigeration stages.
[0241] 28. The method of any of paragraphs 20-27, including cooling
a first fluorocarbon refrigerant of the first fluorocarbon
refrigeration system or a second fluorocarbon refrigerant of the
second fluorocarbon refrigeration system, or both, using a heat
exchanger.
[0242] 29. The method of any of paragraphs 20-28, including cooling
a nitrogen refrigerant of the nitrogen refrigeration system using a
heat exchanger.
[0243] 30. A hydrocarbon processing system for formation of a
liquefied natural gas (LNG), including: [0244] a first
refrigeration system configured to cool a natural gas using a first
fluorocarbon refrigerant, wherein the first refrigeration system
includes a number of first heat exchangers configured to allow for
cooling of the natural gas via an indirect exchange of heat between
the natural gas and the first fluorocarbon refrigerant; [0245] a
second refrigeration system configured to chill the natural gas
using a second fluorocarbon refrigerant, wherein the second
refrigeration system includes a number of second heat exchangers
configured to allow for cooling of the natural gas via an indirect
exchange of heat between the natural gas and the second
fluorocarbon refrigerant; [0246] a third refrigeration system
configured to form LNG from the natural gas using a nitrogen
refrigerant, wherein the third refrigeration system includes a
number of third heat exchangers configured to allow for cooling of
the natural gas via an indirect exchange of heat between the
natural gas and the nitrogen refrigerant; and [0247] a nitrogen
rejection unit configured to remove nitrogen from the LNG.
[0248] 31. The hydrocarbon processing system of paragraph 30,
wherein the nitrogen refrigerant is in a gas phase.
[0249] 32. The hydrocarbon processing system of any of paragraphs
30 or 31, wherein the first heat exchangers include evaporators
configured to cool the natural gas by at least partially vaporizing
the first fluorocarbon refrigerant via a transfer of heat from the
natural gas to the first fluorocarbon refrigerant.
[0250] 33. The hydrocarbon processing system of any of paragraphs
30-32, wherein the second heat exchangers include evaporators
configured to chill the natural gas by at least partially
vaporizing the second fluorocarbon refrigerant via a transfer of
heat from the natural gas to the second fluorocarbon
refrigerant.
[0251] 34. A hydrocarbon processing system for formation of a
liquefied natural gas (LNG), including: [0252] a first fluorocarbon
refrigeration system configured to chill a natural gas using a
first fluorocarbon refrigerant; [0253] a second fluorocarbon
refrigeration system configured to further chill the natural gas
using a second fluorocarbon refrigerant; and [0254] a methane
autorefrigeration system configured to cool the natural gas to
produce LNG.
[0255] 35. The hydrocarbon processing system of paragraph 34,
including a nitrogen rejection unit upstream of the methane
autorefrigeration system.
[0256] 36. The hydrocarbon processing system of any of paragraphs
34 or 35, wherein the methane autorefrigeration system includes a
number of expansion valves and a number of flash drums.
[0257] While the present techniques may be susceptible to various
modifications and alternative forms, the embodiments discussed
herein 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.
* * * * *