Note: Descriptions are shown in the official language in which they were submitted.
LIQUEFACTION OF NATURAL GAS
CROSS-REFERENCE TO RELATED APPLICATION
[000i] [This paragraph is intentionally left blank.]
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.
100041 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.
100051 U.S. Patent 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
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is nitrogen. However, as discussed herein, it may be desirable to produce a
LNG stream within a
refrigeration system that uses nonflammable refrigerants.
SUMMARY
[0006i 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.
[00071 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.
[0908] 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.
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[00091 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
100101 The advantages of the present techniques are better understood by
referring to the
following detailed description and the attached drawings, in which:
100111 Fig. 1 is a process flow diagram of a single stage refrigeration
system;
[00121 Fig. 2 is a process flow diagram of a two stage refrigeration
system including an
economizer;
[00131 Fig. 3 is a process flow diagram of a single stage refrigeration
system including a heat
exchanger economizer;
[00141 Fig. 4 is a process flow diagram of a cascade cooling system
including a first
refrigeration system and a second refrigeration system;
100151 Fig. 5 is process flow diagram of an expansion refrigeration
system for hydrocarbon
dew point control;
[00161 Fig. 6 is a process flow diagram of an expansion refrigeration
system for NGL
production;
100171 Fig. 7 is a process flow diagram of a LNG production system;
[00181 Figs. 8A and 8B are process flow diagrams of a cascade
fluorocarbon with nitrogen
refrigeration cooling system;
100191 Fig. 9 is a process flow diagram of a system including a NRU;
[00201 Figs. 10A and 10B are process flow diagrams of another cascade
fluorocarbon with
nitrogen refrigeration cooling system;
[00211 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;
100221 Figs. 11A and 11B are process flow diagrams of another cascade
cooling system;
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[00231 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;
100241 Fig. 12 is a process flow diagram of a method for the formation
of LNG from a
natural gas stream; and
100251 Fig. 13 is a process flow diagram of another method for the
formation of LNG from a
natural gas stream.
DETAILED DESCRIPTION
[00261 In the following detailed description section, specific embodiments
of the present
techniques arc 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.
[00271 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.
[00281 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.
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[00291 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."
[00301 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.
[00311 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.
[00321 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 C, at least about 5 C, at least about
10 C, at least about 15
C, at least about 25 C, at least about 50 C, at least about 100 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
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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.
100331 "Cryogenic temperature" refers to a temperature that is about ¨50
C or below.
100341 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, CO2, or the like.
[00351 "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 (C2F6). "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 (CHF3), pentafluoroethane (C2HF3), tetrafluoroethane
(C2H2F4),
heptafluoropropane (C3HF7), hexafluoropropane (C3H2F6), pentafluoropropane
(C3H3F3), and
tetrafluoropropane (C3H4F4), among other compounds of similar chemical
structure.
100361 The term "gas" is used interchangeably with "vapor," and is
defined as a substance or
mixture of substances in the gaseous state as distinguished from the liquid or
solid state.
Likewise, the term "liquid" means a substance or mixture of substances in the
liquid state as
distinguished from the gas or solid state.
100371 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.
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"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.
100381 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.
[00391 "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.
[00401 "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 "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.
10042i "Natural gas" refers to a multi-component gas obtained from a
crude oil well or from
a subterranean gas-bearing formation. The composition and pressure of natural
gas can vary
significantly. A typical natural gas stream contains methane (CH4) as a major
component, i.e.,
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greater than 50 mol % of the natural gas stream is methane. The natural gas
stream can also
contain ethane (C2H6), higher molecular weight hydrocarbons (e.g., C3-C20
hydrocarbons), one or
more acid gases (e.g., carbon dioxide or hydrogen sulfide), or any
combinations thereof The
natural gas can also contain minor amounts of contaminants such as water,
nitrogen, iron sulfide,
wax, crude oil, or any combinations thereof The natural gas stream may be
substantially
purified prior to use in embodiments, so as to remove compounds that may act
as poisons or
freeze during the cooling process.
[00431 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.
100441 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% N2. Examples
of types of
NRU's include cryogenic distillation, pressure swing adsorption (PSA),
membrane separation,
lean oil absorption, and solvent absorption.
[00451 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
100461 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,"
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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.
100471 "Substantial" when used in reference to a quantity or amount of a
material, or a
.. specific characteristic thereof, refers to an amount that is sufficient to
provide an effect that the
material or characteristic was intended to provide. The exact degree of
deviation allowable may
depend, in some cases, on the specific context.
Overview
100481 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.
[0949] 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 CO2 removal, LPG production storage,
condensation of reflux in
deethanizers / demethanizers, and natural gas liquefaction to produce LNG.
[00501 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.
[0051] LNG is prepared from a feed gas by refrigeration and liquefaction
technologies.
Optional steps include condensate removal, CO2 removal, dehydration, mercury
removal,
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nitrogen stripping, H2S 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.
100521 Carbon dioxide removal, i.e., separation of methane and lighter
gases from CO2 and
heavier gases, may be achieved with cryogenic distillation processes, such as
the Controlled
Freeze Zone technology available from ExxonMobil Corporation.
100531 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.
Refrigerants
[00541 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
ISCEONO family of refrigerants, the SUVA family of refrigerants, the OPTEON
family of
refrigerants, and the FREON family of refrigerants.
[00551 Multicomponent refrigerants arc 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
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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.
[0056] 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.
Refrigeration Systems
[0057] 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 arc 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.
[0058] 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.
100591 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.
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[00601 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.
100611 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.
100621 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.
[00631 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.
100641 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
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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.
100651 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.
[00661 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.
[00671 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.
100681 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
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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.
100691 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.
[00701 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.
[00711 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.
100721 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.
100731 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
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system 402 or 404 may include mixtures. The cascade cooling system 400 may be
used for
instances in which a higher degree of cooling than that provided by the
refrigeration systems
100, 200, or 300 is desired. The cascade cooling system 400 may provide
cooling at very low
temperatures, e.g., below -40 C. Further, in some embodiments, the cascade
cooling system
400 is implemented upstream of a nitrogen refrigeration system or a methane
autorefrigeration
system.
10074] 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.
10075] 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.
[0076] 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.
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[00771 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.
109781 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.
[00791 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.
109801 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.
10081i Fig. 5 is process flow diagram of an expansion refrigeration
system 500 for
hydrocarbon dew point control. Condensation of heavy hydrocarbons, e.g., C3-
C6, in natural gas
within pipes may result in liquid slugging on pipelines and disruption of gas
receiving facilities.
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Therefore, the hydrocarbon dew point may be reduced using the expansion
refrigeration system
500 in order to prevent such condensation.
[00821 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).
100831 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.
[00841 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.
[00851 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.
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[00861 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 C3s
and higher.
Further, in some embodiments, the heat exchanger 530 is placed upstream of the
expander 516,
with a separator located between the heat exchanger 530 and the expander 516
to prevent liquids
from flowing into the expander 516.
100871 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.
[0081 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.
[00891 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.
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[00901 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.
[00911 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.
[00921 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.
[00931 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.
[00941 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
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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.
100951 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.
100961 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.
[00971 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.
[0981 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.
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I0099j 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.
Systems for the Production of LNG
[0100] 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 'V, or below about -29 C, or below about -
40 'C. In
addition, the cascade cooling system 800 may employ more than one refrigerant
and provide
refrigeration at multiple temperatures.
[0101] 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.
[0102] 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.
[0103] 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
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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.
[0104] 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.
[0105] 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.
[0106] 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
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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.
[0107] 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.
[0108] 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.
[0109] 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.
[0110] 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
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include a fourth heat exchanger 876 and a fifth heat exchanger 878, which may
further cool the
natural gas stream using the fluorocarbon refrigerant.
[0111] 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.
[0112] 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.
[0113] 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.
[0114] 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
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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.
[0115] 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.
[0116] 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.
[0117] 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
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two separate nitrogen refrigerant streams. From the sixth heat exchanger 922,
the nitrogen
refrigerant streams may be combined within a pipe joint 924.
[0118] 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.
[0119] 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.
[0120] 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.
[0121] 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.
[0122] 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.
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[0123] 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.
[0124] 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.
[0125] 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.
[0126] 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
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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.
[0127] 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 Figs. 8A, 8B, or 9. Further, the cascade cooling system
800 or the system
900 may include any number of additional components not shown in Figs. 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.
[0128] 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.
[0129] 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.
[0130] 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.
[0131] 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
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heat exchanger 1010 in place of the heat exchangers 822 824 within the first
fluorocarbon
refrigeration system 802 of Fig. 8A.
[0132] 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.
[0133] 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.
[0134] 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.
[0135] 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
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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.
[0136] 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.
[0137] 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.
[0138] 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
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refrigeration system 1006, which prepares the nitrogen refrigerant stream for
entry into the sixth
heat exchanger 1018.
[0139] 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.
[0140] 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.
[0141] 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.
[0142] 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.
[0143] 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.
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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.
[0144] 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 IOC. 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.
[0145] 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.
[0146] 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-5 08B.
[0147] 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.
[0148] 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
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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.
[0149] 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.
[0150] 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.
[0151] 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.
[0152] 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
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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.
[0153] 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.
[0154] 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.
[0155] 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,
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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.
[0156] 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.
[0157] 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.
[0158] 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.
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[0159] 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.
[0160] 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.
[0161] 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.
[0162] 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.
[0163] 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.
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[0164] 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.
[0165] 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 Figs. 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 Figs. 11A, 11B, or 11C, respectively, depending on the
details of the
specific implementation.
[0166] 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.
Method for LNG Formation
[0167] 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,
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a hydrofluorocarbon refrigerant, such as R-410A, or any other suitable type of
fluorocarbon
refrigerant.
[0168] 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.
[0169] 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.
[0170] 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.
[0171] 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
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cooling fluid. The natural gas stream may then be chilled within the heat
exchange area using
the expanded, cooled second fluorocarbon refrigerant.
[0172] 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.
[0173] 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.
[0174] 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.
[0175] 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.
[0176] 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.
-39-
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.
[0177] 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.
[0178] 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
[01791 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.
101801 A
hydrocarbon processing system for formation of a liquefied natural gas (LNG),
including:
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.
[0181] The hydrocarbon processing system of paragraph [0180], wherein
the first fluorocarbon
refrigeration system is configured to cool the second fluorocarbon refrigerant
of the second
fluorocarbon refrigeration system.
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[0182] The hydrocarbon processing system of any of paragraphs [0180] or [0181
],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.
[0183] The hydrocarbon processing system of any of paragraphs [0180]-[0182],
wherein the first
fluorocarbon refrigeration system or the second fluorocarbon refrigeration
system, or both,
includes multiple cooling cycles.
[0184] The hydrocarbon processing system of any of paragraphs [0180]-[0183],
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.
[0185] The hydrocarbon processing system of any of paragraphs [0180]-[0184],
wherein the first
fluorocarbon refrigeration system includes:
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.
[01861 The hydrocarbon processing system of any of paragraphs [0180]40185],
wherein the second
fluorocarbon refrigeration system includes:
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
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a heat exchanger configured to cool the natural gas via indirect heat exchange
with the
cooled second fluorocarbon refrigerant.
101871 The hydrocarbon processing system of any of paragraphs [0180]40186],
wherein the first
fluorocarbon refrigerant includes R-410A.
[0188] The hydrocarbon processing system of any of paragraphs [0180[40187],
wherein the second
fluorocarbon refrigerant includes R-5 08B.
[0189] The hydrocarbon processing system of any of paragraphs [0180[40188],
wherein the first
fluorocarbon refrigerant or the second fluorocarbon refrigerant, or both,
includes a nontoxic,
nonflammable refrigerant.
[0190] The hydrocarbon processing system of any of paragraphs [0180]-[01891,
wherein the first
fluorocarbon refrigeration system or the second fluorocarbon refrigeration
system, or both,
includes two or more chillers and two or more compressors.
[0191] The hydrocarbon processing system of any of paragraphs [0180]40190],
wherein the first
fluorocarbon refrigeration system and the second fluorocarbon refrigeration
system are
implemented in series.
[0192] The hydrocarbon processing system of any of paragraphs [0180[40191],
wherein the
nitrogen refrigerant is in a gas phase.
101931 The hydrocarbon processing system of any of paragraphs
[0180140192], wherein the
nitrogen refrigeration system includes two or more chillers, two or more
expanders, and two or
more compressors.
[0194] The hydrocarbon processing system of any of paragraphs r0180]-
[0193], wherein the
hydrocarbon processing system is configured to chill the natural gas for
hydrocarbon dew point
control.
[0195] The hydrocarbon processing system of any of paragraphs [0180]-
[0194], wherein the
hydrocarbon processing system is configured to chill the natural gas for
natural gas liquid
extraction.
[0196] The hydrocarbon processing system of any of paragraphs
[0180[40195], wherein the
hydrocarbon processing system is configured to separate methane and lighter
gases from carbon
dioxide and heavier gases.
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[0197] The
hydrocarbon processing system of any of paragraphs [0180[40196], wherein the
hydrocarbon processing system is configured to prepare hydrocarbons for
liquefied petroleum
gas production storage.
[0198] The
hydrocarbon processing system of any of paragraphs [0180]40197], wherein the
hydrocarbon processing system is configured to condense a reflux stream.
101991 A method for formation of a liquefied natural gas (LNG),
including:
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.
[0200] The method of paragraph [0199], including cooling a second fluorocarbon
refrigerant
of the second fluorocarbon refrigeration system within the first fluorocarbon
refrigeration
system.
[0201] The method of any of paragraphs [0199] or [0200], including
cooling a nitrogen
refrigerant of the nitrogen refrigeration system within the first fluorocarbon
refrigeration system
or the second fluorocarbon refrigeration system, or both.
102021 The method of any of paragraphs [0199] or [0201], wherein cooling the
natural gas in the
first fluorocarbon refrigeration system includes:
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, coo led 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.
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[02031 The method of any of paragraphs [0199]-[0202], wherein cooling the
natural gas in the
second fluorocarbon refrigeration system includes:
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.
[02041 The method of any of paragraphs [0199[40203], including maintaining
a nitrogen
refrigerant of the nitrogen refrigeration system in a gas phase using one or
more expansion
turbines.
[0205] The method of any of paragraphs [0199140204], 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.
[02061 The method of any of paragraphs 10199140205], including liquefying the
natural gas in
the nitrogen refrigeration system using one or more refrigeration stages.
[02071 The method of any of paragraphs [0199[40206], including coiling 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.
[02081 The method of any of paragraphs [0199]-[0207], including cooling a
nitrogen refrigerant
of the nitrogen refrigeration system using a heat exchanger.
102091 A hydrocarbon processing system for formation of a liquefied natural
gas (LNG),
including:
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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;
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;
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
a nitrogen rejection unit configured to remove nitrogen from the LNG.
[0210] The hydrocarbon processing system of paragraph [0209], wherein the
nitrogen
refrigerant is in a gas phase.
[0211] The
hydrocarbon processing system of any of paragraphs [0209] or [0210], 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.
102121 The hydrocarbon processing system of any of paragraphs [0209]-[0211],
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.
[0213] A hydrocarbon processing system for formation of a liquefied natural
gas (LNG),
including:
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.
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[0214] The hydrocarbon processing system of paragraph [0213], including
a nitrogen
rejection unit upstream of the methane autorefrigeration system.
[0215] The hydrocarbon processing system of any of paragraphs [0213] or
[0214], wherein the
methane autorcfrigeration system includes a number of expansion valves and a
number of flash
drums.
[0216] 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.
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