U.S. patent application number 15/882624 was filed with the patent office on 2018-05-31 for liquefied natural gas production.
The applicant listed for this patent is Michael R. Miller, Russell H. Oelfke. Invention is credited to Michael R. Miller, Russell H. Oelfke.
Application Number | 20180149424 15/882624 |
Document ID | / |
Family ID | 51227940 |
Filed Date | 2018-05-31 |
United States Patent
Application |
20180149424 |
Kind Code |
A1 |
Oelfke; Russell H. ; et
al. |
May 31, 2018 |
Liquefied Natural Gas Production
Abstract
Hydrocarbon processing systems and a method for liquefied
natural gas (LNG) production are described herein. The hydrocarbon
processing system includes a fluorocarbon refrigeration system
configured to cool a natural gas to produce LNG using a mixed
fluorocarbon refrigerant and a nitrogen rejection unit (NRU)
configured to remove nitrogen from the LNG.
Inventors: |
Oelfke; Russell H.;
(Houston, TX) ; Miller; Michael R.; (Houston,
TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Oelfke; Russell H.
Miller; Michael R. |
Houston
Houston |
TX
TX |
US
US |
|
|
Family ID: |
51227940 |
Appl. No.: |
15/882624 |
Filed: |
January 29, 2018 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14649056 |
Jun 2, 2015 |
|
|
|
PCT/US13/74909 |
Dec 13, 2013 |
|
|
|
15882624 |
|
|
|
|
61756322 |
Jan 24, 2013 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 1/004 20130101;
F25J 1/0097 20130101; F25J 1/023 20130101; F25J 1/0292 20130101;
F25J 1/0052 20130101; F25J 1/0264 20130101; F25J 1/0072 20130101;
F25J 2220/62 20130101; F25J 1/0042 20130101; F25J 1/0022 20130101;
F25J 1/0215 20130101; F25J 1/005 20130101; F25J 1/0219 20130101;
F25J 2210/06 20130101; F25J 1/0212 20130101; F25J 1/0045 20130101;
F25J 1/0035 20130101; F25J 1/0231 20130101; F25J 1/0214 20130101;
F25J 1/0265 20130101; F25J 2210/04 20130101; F25J 2220/64 20130101;
F25J 1/0055 20130101; F25J 2245/02 20130101 |
International
Class: |
F25J 1/00 20060101
F25J001/00; F25J 1/02 20060101 F25J001/02 |
Claims
1. A hydrocarbon processing system for liquefied natural gas (LNG)
production, comprising: a fluorocarbon refrigeration system
configured to cool a natural gas to produce LNG using a mixed
fluorocarbon refrigerant; a nitrogen rejection unit (NRU)
configured to remove nitrogen from the LNG; and an
autorefrigeration system configured to further cool the natural gas
to produce the LNG.
2. The hydrocarbon processing system of claim 1, comprising a
nitrogen refrigeration system configured to further cool the
natural gas to produce the LNG using a nitrogen refrigerant.
3. (canceled)
4. The hydrocarbon processing system of claim 1, wherein the
autorefrigeration system comprises a plurality of flash drums and a
plurality of expansion devices.
5. The hydrocarbon processing system of claim 1, wherein at least a
portion of the natural gas is cooled using a nitrogen stream
separated from the natural gas via the NRU.
6. The hydrocarbon processing system of claim 1, wherein the
fluorocarbon refrigeration system comprises a single mixed
refrigerant cycle.
7. The hydrocarbon processing system of claim 1, wherein the
fluorocarbon refrigeration system comprises a pre-cooled mixed
refrigerant cycle.
8. The hydrocarbon processing system of claim 1, wherein the
fluorocarbon refrigeration system comprises a dual mixed
refrigerant cycle.
9. The hydrocarbon processing system of claim 8, wherein the dual
mixed refrigerant cycle comprises: a first mixed refrigerant cycle
that uses a warm mixed fluorocarbon refrigerant; and a second mixed
refrigerant cycle that uses a cold mixed fluorocarbon refrigerant,
wherein the first mixed refrigerant cycle and the second mixed
refrigerant cycle are connected in series.
10. The hydrocarbon processing system of claim 1, wherein the
fluorocarbon refrigeration system comprises a triple mixed
refrigerant cycle.
11. The hydrocarbon processing system of claim 1, wherein the
fluorocarbon refrigeration system comprises a heat exchanger
configured to allow for cooling of the natural gas via an indirect
exchange of heat between the natural gas and the mixed fluorocarbon
refrigerant.
12. The hydrocarbon processing system of claim 1, wherein the
fluorocarbon refrigeration system comprises: a compressor
configured to compress the mixed fluorocarbon refrigerant to
provide a compressed mixed fluorocarbon refrigerant; a chiller
configured to cool the compressed mixed fluorocarbon refrigerant to
provide a cooled mixed fluorocarbon refrigerant; and a heat
exchanger configured to cool the natural gas via indirect heat
exchange with the cooled mixed fluorocarbon refrigerant.
13. The hydrocarbon processing system of claim 1, wherein the
hydrocarbon processing system is configured to chill the natural
gas for hydrocarbon dew point control.
14. The hydrocarbon processing system of claim 1, wherein the
hydrocarbon processing system is configured to chill the natural
gas for natural gas liquid extraction.
15. The hydrocarbon processing system of claim 1, wherein the
hydrocarbon processing system is configured to separate methane and
lighter gases from carbon dioxide and heavier gases.
16. The hydrocarbon processing system of claim 1, wherein the
hydrocarbon processing system is configured to prepare hydrocarbons
for liquefied petroleum gas production storage.
17. The hydrocarbon processing system of claim 1, wherein the
hydrocarbon processing system is configured to condense a reflux
stream.
18. A method for liquefied natural gas (LNG) production,
comprising: cooling a natural gas to produce LNG in a fluorocarbon
refrigeration system using a mixed fluorocarbon refrigerant;
[[and]] removing nitrogen from the LNG in a nitrogen rejection unit
(NRU); and further cooling the natural gas to produce the LNG in an
autorefrigeration system.
19. The method of claim 18, comprising further cooling the natural
gas to produce the LNG in a nitrogen refrigeration system using a
nitrogen refrigerant.
20. (canceled)
21. The method of claim 18, comprising cooling at least a portion
of the natural gas using a nitrogen stream separated from the
natural gas via the NRU.
22. The method of claim 18, wherein cooling the natural gas in the
fluorocarbon refrigeration system comprises: compressing the mixed
fluorocarbon refrigerant to provide a compressed mixed fluorocarbon
refrigerant; cooling the compressed mixed fluorocarbon refrigerant
by indirect heat exchange with a cooling fluid to provide a cooled
mixed fluorocarbon refrigerant; passing the cooled mixed
fluorocarbon refrigerant to a heat exchange area; and heat
exchanging the natural gas with the cooled mixed fluorocarbon
refrigerant in the heat exchange area.
23. A hydrocarbon processing system for formation of a liquefied
natural gas (LNG), comprising: a mixed refrigerant cycle configured
to cool a natural gas using a mixed fluorocarbon refrigerant,
wherein the mixed refrigerant cycle comprises a heat exchanger
configured to allow for cooling of the natural gas via an indirect
exchange of heat between the natural gas and the mixed fluorocarbon
refrigerant; a nitrogen rejection unit (NRU) configured to remove
nitrogen from the natural gas; and a methane autorefrigeration
system configured to cool the natural gas to produce the LNG.
24. The hydrocarbon processing system of claim 23, wherein the
mixed fluorocarbon refrigerant comprises a mixture of two or more
hydrofluorocarbon refrigerants.
25. The hydrocarbon processing system of claim 23, wherein a
nitrogen stream separated from the natural gas via the NRU is used
to cool at least a portion of the natural gas.
26. The hydrocarbon processing system of claim 23, wherein the
methane autorefrigeration system comprises a plurality of expansion
devices and a plurality of flash drums.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application 61/756,322 filed 24 Jan. 2013 entitled LIQUEFIED
NATURAL GAS PRODUCTION, the entirety of which is incorporated by
reference herein.
FIELD OF THE INVENTION
[0002] The present techniques relate generally to the field of
hydrocarbon recovery and treatment processes and, more
particularly, to a method and systems for liquefied natural gas
(LNG) production via a refrigeration process that uses mixed
fluorocarbon refrigerants.
BACKGROUND
[0003] This section is intended to introduce various aspects of the
art, which may be associated with exemplary embodiments of the
present techniques. This discussion is believed to assist in
providing a framework to facilitate a better understanding of
particular aspects of the present techniques. Accordingly, it
should be understood that this section should be read in this
light, and not necessarily as admissions of prior art.
[0004] Many low temperature refrigeration systems that are used for
natural gas processing and liquefaction rely on the use of single
component refrigerants or mixed refrigerants (MRs) including
hydrocarbons components to provide external refrigeration. For
example, liquefied natural gas (LNG) may be produced using a mixed
refrigerant including hydrocarbon components extracted from a feed
gas. Such hydrocarbon components may include methane, ethane,
ethylene, propane, and the like.
[0005] U.S. Pat. No. 6,412,302 to Foglietta et al. describes a
process for producing a liquefied natural gas stream. The process
includes cooling at least a portion of a pressurized natural gas
feed stream by heat exchange contact with first and second expanded
refrigerants that are used in independent refrigeration cycles. The
first expanded refrigerant is selected from methane, ethane, and
treated and pressurized natural gas, while the second expanded
refrigerant is nitrogen. Therefore, such techniques rely on the use
of refrigerants including hydrocarbons, which are flammable.
[0006] U.S. Patent Application Publication No. 2010/0281915 by
Roberts et al. describes a system and method for liquefying a
natural gas stream. A dehydrated natural gas stream is pre-cooled
in a pre-cooling apparatus that uses a pre-coolant consisting of a
HFC refrigerant. The pre-cooled dehydrated natural gas stream is
then cooled in a main heat exchanger through indirect heat exchange
against a vaporized hydrocarbon mixed refrigerant coolant to
produce LNG. The mixed refrigerant coolant includes ethane,
methane, nitrogen, and less than or equal to 3 mol % of propane.
Therefore, such techniques also rely on the use of refrigerants
including hydrocarbons.
[0007] U.S. Patent Application Publication No. 2012/0047943 by
Barclay et al. describes a process for offshore liquefaction of a
natural gas feed. The process includes contacting the natural gas
feed with a biphasic refrigerant at a first temperature, contacting
the natural gas feed with a first gaseous refrigerant at a second
temperature, and contacting the natural gas feed with a second
gaseous refrigerant at a third temperature. The refrigerated
natural gas feed is then expanded using an expansion device to form
a flash gas stream and a liquefied natural gas stream. The biphasic
refrigerant may be a commercial refrigerant such as R507 or R134a,
or a mixture thereof. The first gaseous refrigerant may be
nitrogen. The second gaseous refrigerant may be the flash gas
stream recovered from the natural gas feed. The biphasic
refrigerant is used to cool and partially condense the natural gas
feed in a feed gas chiller, while the first and second gaseous
refrigerants are used to cool and condense the natural gas feed in
a main cryogenic heat exchanger. Therefore, such techniques rely on
the use of a refrigerant including hydrocarbon components extracted
from the natural gas feed.
[0008] U.S. Pat. No. 6,631,625 to Weng describes a
non-hydrochlorofluorocarbon (non-HCFC) design of a refrigerant
mixture for an ultra-low temperature refrigeration system. The
non-HCFC refrigerant mixture is primarily composed of
hydrofluorocarbon (HFC) refrigerants and hydrocarbons. Therefore,
such techniques also rely on the use of refrigerants including
hydrocarbons. Furthermore, the use of such refrigerant mixtures for
natural gas processing or liquefaction is not disclosed.
SUMMARY
[0009] An embodiment provides a hydrocarbon processing system for
liquefied natural gas (LNG) production. The hydrocarbon processing
system includes a fluorocarbon refrigeration system configured to
cool a natural gas to produce LNG using a mixed fluorocarbon
refrigerant and a nitrogen rejection unit (NRU) configured to
remove nitrogen from the LNG.
[0010] Another embodiment provides a method for liquefied natural
gas (LNG) production. The method includes cooling a natural gas to
produce LNG in a fluorocarbon refrigeration system using a mixed
fluorocarbon refrigerant and removing nitrogen from the LNG in a
nitrogen rejection unit (NRU).
[0011] Another embodiment provides a hydrocarbon processing system
for the formation of a liquefied natural gas (LNG). The hydrocarbon
processing system includes a mixed refrigerant cycle configured to
cool a natural gas using a mixed fluorocarbon refrigerant, wherein
the mixed refrigerant cycle includes a heat exchanger configured to
allow for cooling of the natural gas via an indirect exchange of
heat between the natural gas and the mixed fluorocarbon
refrigerant. The hydrocarbon processing system also includes a
nitrogen rejection unit (NRU) configured to remove nitrogen from
the natural gas and a methane autorefrigeration system configured
to cool the natural gas to produce the LNG.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The advantages of the present techniques are better
understood by referring to the following detailed description and
the attached drawings, in which:
[0013] FIG. 1 is a process flow diagram of a single stage
refrigeration system;
[0014] FIG. 2 is a process flow diagram of a two stage
refrigeration system including an economizer;
[0015] FIG. 3 is a process flow diagram of a single stage
refrigeration system including a heat exchanger economizer;
[0016] FIG. 4 is a process flow diagram of a liquefied natural gas
(LNG) production system;
[0017] FIG. 5 is a process flow diagram of a hydrocarbon processing
system including a single mixed refrigerant (SMR) cycle;
[0018] FIG. 6 is a process flow diagram of the hydrocarbon
processing system of FIG. 5 with the addition of a nitrogen
refrigeration system;
[0019] FIG. 7 is a process flow diagram of the hydrocarbon
processing system of FIG. 5 with the addition of a methane
autorefrigeration system;
[0020] FIG. 8 is a process flow diagram of a hydrocarbon processing
system including a pre-cooled SMR cycle;
[0021] FIG. 9 is a process flow diagram of a hydrocarbon processing
system including a dual mixed refrigerant (DMR) cycle;
[0022] FIGS. 10A and 10B are process flow diagrams of a hydrocarbon
processing system including an SMR cycle, an NRU, and a methane
autorefrigeration system;
[0023] FIGS. 11A and 11B are process flow diagrams of a hydrocarbon
processing system including an economized DMR cycle, an NRU, and a
methane autorefrigeration system; and
[0024] FIG. 12 is a process flow diagram of a method for the
formation of LNG from a natural gas stream using a mixed
fluorocarbon refrigerant.
DETAILED DESCRIPTION
[0025] In the following detailed description section, specific
embodiments of the present techniques are described. However, to
the extent that the following description is specific to a
particular embodiment or a particular use of the present
techniques, this is intended to be for exemplary purposes only and
simply provides a description of the exemplary embodiments.
Accordingly, the techniques are not limited to the specific
embodiments described herein, but rather, include all alternatives,
modifications, and equivalents falling within the spirit and scope
of the appended claims.
[0026] 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.
[0027] 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.
[0028] 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."
[0029] The "boiling point" or "BP" of a substance is the
temperature at which the vapor pressure of the liquid equals the
pressure surrounding the liquid and, thus, the liquid changes into
a vapor. The "normal boiling point" or "NBP" of a substance is the
boiling point at a pressure of one atmosphere, i.e., 101.3
kilopascals (kPa).
[0030] A "compressor" includes any unit, device, or apparatus able
to increase the pressure of a stream. This includes compressors
having a single compression process or step, or compressors having
multi-stage compression processes or steps, more particularly
multi-stage compressors within a single casing or shell. Evaporated
streams to be compressed can be provided to a compressor at
different pressures. For example, some stages or steps of a
hydrocarbon cooling process may involve two or more refrigerant
compressors in parallel, series, or both. The present techniques
are not limited by the type or arrangement or layout of the
compressor or compressors, particularly in any refrigeration
cycle.
[0031] As used herein, "cooling" broadly refers to lowering and/or
dropping a temperature and/or internal energy of a substance, such
as by any suitable amount. Cooling may include a temperature drop
of at least about 1.degree. C., at least about 5.degree. C., at
least about 10.degree. C., at least about 15.degree. C., at least
about 25.degree. C., at least about 50.degree. C., at least about
100.degree. C., and/or the like. The cooling may use any suitable
heat sink, such as steam generation, hot water heating, cooling
water, air, refrigerant, other process streams (integration), and
combinations thereof. One or more sources of cooling may be
combined and/or cascaded to reach a desired outlet temperature. The
cooling step may use a cooling unit with any suitable device and/or
equipment. According to one embodiment, cooling may include
indirect heat exchange, such as with one or more heat exchangers.
Heat exchangers may include any suitable design, such as shell and
tube, brazed aluminum, spiral wound, and/or the like. In the
alternative, the cooling may use evaporative (heat of vaporization)
cooling, sensible heat cooling, and/or direct heat exchange, such
as a liquid sprayed directly into a process stream.
[0032] "Cryogenic temperature" refers to a temperature that is
about -50.degree. C. or below.
[0033] As used herein, the terms "deethanizer" and "demethanizer"
refer to distillation columns or towers that may be used to
separate components within a natural gas stream. For example, a
demethanizer is used to separate methane and other volatile
components from ethane and heavier components. The methane fraction
is typically recovered as purified gas that contains small amounts
of inert gases such as nitrogen, CO.sub.2, or the like.
[0034] "Fluorocarbons," also referred to as "perfluorocarbons" or
"PFCs," are molecules including F and C atoms. Fluorocarbons have
F--C bonds and, depending on the number of carbon atoms in the
species, C--C bonds. An example of a fluorocarbon includes
hexafluoroethane (C.sub.2F.sub.6). "Hydrofluorocarbons" or "HFCs"
are a specific type of fluorocarbon including H, F, and C atoms.
Hydrofluorocarbons have H--C and F--C bonds and, depending on the
number of carbon atoms in the species, C--C bonds. Some examples of
hydrofluorocarbons include fluoroform (CHF.sub.3),
pentafluoroethane (C.sub.2HF.sub.5), tetrafluoroethane
(C.sub.2H.sub.2F.sub.4), heptafluoropropane (C.sub.3HF.sub.7),
hexafluoropropane (C.sub.3H.sub.2F.sub.6), pentafluoropropane
(C.sub.3H.sub.3F.sub.5), and tetrafluoropropane
(C.sub.3H.sub.4F.sub.4), among other compounds of similar chemical
structure. Hydrofluorocarbons with unsaturated bonds are referred
to as "hydrofluoroolefins" or "HFOs." HFOs are typically more
reactive and flammable than HFCs due to the presence of unsaturated
bonds. However, HFOs also typically degrade in the environment
faster than HFCs.
[0035] 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.
[0036] The term "greenhouse gases" broadly refers to gases or
vapors in an atmosphere that can absorb and/or emit radiation
within the thermal infrared range. Examples include carbon
monoxide, carbon dioxide, water vapor, methane, ethane, propane,
ozone, hydrogen sulfide, sulfur oxides, nitrogen oxides,
halocarbons, chlorofluorocarbons, or the like. Electrical power
plants, petroleum refineries, and other energy conversion
facilities can tend to be large sources of greenhouses gases
emitted to the atmosphere. Without being bound by theory,
greenhouse gases are believed to receive and/or retain solar
radiation and energy, which become trapped in the atmosphere. This
may result in an increase in average global atmospheric
temperatures and other climate changes.
[0037] The "global-warming potential" or "GWP" of a gas is a
relative measure of how much heat the gas traps in the atmosphere.
GWP compares the amount of heat trapped by a certain mass of the
gas in question to the amount of heat trapped by a similar mass of
carbon dioxide. GWP is calculated over a specific time interval,
such as 20, 100 or 500 years. GWP is expressed as a factor of
carbon dioxide, wherein carbon dioxide has a standardized GWP of 1.
For example, the 20 year GWP, i.e., GWP.sub.20, of methane is 72.
This means that, if the same mass of methane and carbon dioxide are
introduced into the atmosphere, the methane will trap 72 times more
heat than the carbon dioxide over the next 20 years.
[0038] A "heat exchanger" broadly means any device capable of
transferring heat from one media to another media, including
particularly any structure, e.g., device commonly referred to as a
heat exchanger. Heat exchangers include "direct heat exchangers"
and "indirect heat exchangers." Thus, a heat exchanger may be a
shell-and-tube, spiral, hairpin, core, core-and-kettle,
double-pipe, brazed aluminum, spiral wound, or any other type of
known heat exchanger. "Heat exchanger" may also refer to any
column, tower, unit or other arrangement adapted to allow the
passage of one or more streams there through, and to affect direct
or indirect heat exchange between one or more lines of refrigerant,
and one or more feed streams.
[0039] 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.
[0040] "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.
[0041] "Liquefied petroleum gas" 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.
[0042] The "melting point" or "MP" of a substance is the
temperature at which the solid and liquid forms of the substance
can exist in equilibrium. As heat is applied to the solid form of a
substance, its temperature will increase until the melting point is
reached. The application of additional heat will then convert the
substance from solid form to liquid form with no temperature
change. When the entire substance has melted, additional heat will
raise the temperature of the liquid form of the substance.
[0043] "Mixed refrigerant processes" or "MR processes" may include,
but are not limited to, a "single mixed refrigerant" or "SMR"
cycle, a hydrocarbon pre-cooled MR cycle, a "dual mixed
refrigerant" or "DMR" cycle, and a "triple mixed refrigerant" or
"TMR" cycle. In general, MRs can include hydrocarbon and/or
non-hydrocarbon components. MR processes employ at least one mixed
component refrigerant, but can additionally employ one or more
pure-component refrigerants as well.
[0044] "Natural gas" refers to a multi-component gas obtained from
a crude oil well or from a subterranean gas-bearing formation. The
composition and pressure of natural gas can vary significantly. A
typical natural gas stream contains methane (CH.sub.4) as a major
component, i.e., greater than 50 mol % of the natural gas stream is
methane. The natural gas stream can also contain ethane
(C.sub.2H.sub.6), higher molecular weight hydrocarbons (e.g.,
C.sub.3-C.sub.20 hydrocarbons), one or more acid gases (e.g.,
carbon dioxide or hydrogen sulfide), or any combinations thereof.
The natural gas can also contain minor amounts of contaminants such
as water, nitrogen, iron sulfide, wax, crude oil, or any
combinations thereof. The natural gas stream may be substantially
purified prior to use in embodiments, so as to remove compounds
that may act as poisons.
[0045] As used herein, "natural gas liquids" or "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.
[0046] A "nitrogen rejection unit" or "NRU" refers to any system or
device configured to receive a natural gas feed stream and produce
substantially pure products streams, e.g., a salable methane stream
and a nitrogen stream including about 30% to 99% N.sub.2. Examples
of types of NRU's include cryogenic distillation, pressure swing
adsorption (PSA), membrane separation, lean oil absorption, and
solvent absorption.
[0047] The "ozone depletion potential" or "ODP" of a chemical
compound is the relative amount of degradation to the ozone layer
it can cause, where trichlorofluoromethane, i.e., R-11, is fixed at
an ODP of 1.0. Chlorodifluoromethane, i.e., R-22, for example, has
an ODP of 0.055. Many HFCs, such as R-32, have ODPs approaching
zero.
[0048] 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.
[0049] Refrigerant components often include single component
refrigerants. A single component refrigerant with a single
halogenated hydrocarbon has an associated "R-" designation of two
or three numbers, which reflects its chemical composition. Adding
90 to the number gives three digits that stand for the number of
carbon, hydrogen, and fluorine atoms, respectively. The first digit
of a refrigerant with three numbers is one unit lower than the
number of carbon atoms in the molecule. If the molecule contains
only one carbon atom, the first digit is omitted. The second digit
is one unit greater than the number of hydrogen atoms in the
molecule. The third digit is equal to the number of fluorine atoms
in the molecule. Remaining bonds not accounted for are occupied by
chlorine atoms. A suffix of a lower-case letter "a," "b," or "c"
indicates increasingly unsymmetrical isomers. As a special case,
the R-400 series is made up of zeotropic blends, and the R-500
series is made up of azeotropic blends. The rightmost digit is
assigned arbitrarily by ASHRAE, an industry organization.
[0050] "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
[0051] Embodiments described herein provide a hydrocarbon
processing system. The hydrocarbon processing system includes a
refrigeration system for producing LNG from a natural gas. The
refrigeration system includes a fluorocarbon refrigeration system
that utilizes a mixed fluorocarbon refrigerant to cool the natural
gas. The refrigeration system may also include a nitrogen
refrigeration system and/or a methane autorefrigeration system,
which may be used to further cool the natural gas to produce LNG.
In addition, the hydrocarbon processing system may include an NRU,
which may be used to remove nitrogen from the natural gas. In some
embodiments, the nitrogen that is removed from the natural gas via
the NRU is used to provide additional cooling for the natural
gas.
[0052] Hydrocarbon processing systems include any number of systems
known to those skilled in the art. Hydrocarbon production and
treatment processes include, but are not limited to, chilling
natural gas for NGL extraction, chilling natural gas for
hydrocarbon dew point control, chilling natural gas for CO.sub.2
removal, LPG production storage, condensation of reflux in
deethanizers or demethanizers, and natural gas liquefaction to
produce LNG.
[0053] 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.
[0054] LNG is prepared from a feed gas by refrigeration and
liquefaction technologies. Optional steps include condensate
removal, CO.sub.2 removal, dehydration, mercury removal, nitrogen
stripping, H.sub.2S removal, and the like. After liquefaction, LNG
may be stored or loaded on a tanker for sale or transport.
Conventional liquefaction processes can include: APCI Propane
pre-cooled mixed refrigerant; C.sub.3MR; DUAL MR; Phillips
Optimized Cascade; Prico SMR; TEAL dual pressure mixed refrigerant;
Linde/Statoil multi fluid cascade; Axens DMR; ExxonMobil's Enhanced
Mixed Refrigerant (EMR); and the Shell processes C.sub.3MR and
DMR.
[0055] Carbon dioxide removal, i.e., separation of methane and
lighter gases from CO.sub.2 and heavier gases, may be achieved with
cryogenic distillation processes, such as the Controlled Freeze
Zone technology available from ExxonMobil Corporation.
[0056] 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 CO.sub.2 and heavier gases, prepare hydrocarbons for LPG
production, or condense a reflux stream in deethanizers and/or
demethanizers, among others.
Refrigerants
[0057] The refrigerants that are utilized according to embodiments
described herein may be mixed refrigerants, where each mixed
refrigerant may include two or more single component and/or
multicomponent refrigerants. 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. In
various embodiments, the mixed refrigerants that are utilized
according to embodiments described herein include fluorocarbons
(FCs), such as HFCs. Exemplary refrigerants are commercially
available from DuPont Corporation, including the ISCEON.RTM. family
of refrigerants, the SUVA.RTM. family of refrigerants, the
OPTEON.RTM. family of refrigerants, and the FREON.RTM. family of
refrigerants.
[0058] Multicomponent refrigerants are commercially available. For
example, R-401A is a HCFC blend of R-32, R-152a, and R-124. R-404A
is a HFC blend of 52 wt. % R-143a, 44 wt. % R-125, and 4 wt. %
R-134a. R-406A is a blend of 55 wt. % R-22, 4 wt. % R-600a, and 41
wt. % R-142b. R-407A is a HFC blend of 20 wt. % R-32, 40 wt. %
R-125, and 40 wt. % R-134a. R-407C is a hydrofluorocarbon blend of
R-32, R-125, and R-134a. R-408A is a HCFC blend of R-22, R-125, and
R-143a. R-409A is a HCFC blend of R-22, R-124, and R-142b. R-410A
is a blend of R-32 and R-125. R-500 is a blend of 73.8 wt. % R-12
and 26.2 wt. % of R-152a. R-502 is a blend of R-22 and R-115.
R-508B is a blend of R-23 and R-116. More specific information
regarding particular refrigerants that may be used according to
embodiments described herein is shown below in Table 1.
[0059] The ozone depletion potentials for all the refrigerants
shown in Table 1 are equal to zero. The "Safety Group" shown in
Table 1 is an ASHRAE designation. A designation of "A" indicates
that the Occupational Exposure Limit (OEL) for the refrigerant is
above 400 parts per million (ppm). A designation of "B" indicates
that the OEL for the refrigerant is below 400 ppm. A number of "1"
indicates that the refrigerant is non-flammable. A number of "2"
indicates that the refrigerant is slightly flammable, and a number
of "3" indicates that the refrigerant is highly flammable. An "L"
suffix indicates that the refrigerant has a very low flame
propagation speed.
[0060] It is to be understood that the embodiments described herein
are not limited to the use of the refrigerants listed in Table 1.
Rather, any other suitable types of non-flammable refrigerants, or
mixtures thereof, may also be used according to embodiments
described herein. For example, any suitable types of HFCs, HFOs,
and/or inert compounds can be combined to form a mixed refrigerant
according to embodiments described herein.
TABLE-US-00001 TABLE 1 Refrigerants Atm. ASHRAE NBP MP Safety Life
Number Chemical Name Formula MW .degree. C. .degree. C. Group years
GWP.sub.100 R-50 Methane CH.sub.4 16 -162 -182 A3 12 25 R-14
Tetrafluoro methane CF.sub.4 88 -128 -183 A1 50,000 7,390 R-23
Trifluoro methane CHF.sub.3 70 -82 -155 A1 270 14,800 R-41 Fluoro
methane CH.sub.3F 34 -78 -142 A3 2.4 92 R-32 Difluoro methane
CH.sub.2F.sub.2 52 -52 -136 A2L 4.9 675 R-218 Octafluoro propane
C.sub.3F.sub.8 188 -37 -148 A1 2,600 8,830 R-227ea
1,1,1,2,3,3,3-heptafluoro propane CF.sub.3CFHCF.sub.3 170 -16 -131
A1 34.2 3,220 R-245fa 1,1,1,3,3-pentafluoro propane
CF.sub.3CH.sub.2CHF.sub.2 134 15 -102 B1 7.6 1,030 R-116 Hexafluoro
ethane C.sub.2F.sub.6 138 -78 -101 A1 10,000 12,200 R-125 1,1,1,2,2
Pentafluoro ethane C.sub.2HF.sub.5 120 -49 -103 A1 29 3,500 R-143a
1,1,1-trifluoro ethane CH.sub.3CF.sub.3 84 -48 -111 A2L 52 4,470
R-1234yf 2,3,3,3-Tetrafluoropropene C.sub.3H.sub.2F.sub.4 114 -29
-152 A2L 0.03 0 R-134a 1,1,1,2-tetrafluoro ethane CH.sub.2FCF.sub.3
102 -26 -103 A1 14 1,430 R-152a 1,1difluoro ethane
CH.sub.2CHF.sub.2 66 -25 -117 A2 1.4 124 R-1234ze
1,3,3,3-Tetrafluoropropene C.sub.3H.sub.2F.sub.4 114 -19 -- A2L --
0 R-C318 Octafluoro cyclobutane (--CF.sub.2--).sub.4 200 -6 -40 A1
3,200 10,300 R-236fa 1,1,1,3,3,3-hexafluoro propane
CF.sub.3CH.sub.2CF.sub.3 152 -2 -96 A1 240 9,810 R-245ca
1,1,2,2,3-pentafluoro propane CHF.sub.2CF.sub.2CH.sub.2F 134 25 -82
B1 6.2 693 HFE-347mcc Heptafluoropropyl, methyl ether
C.sub.3F.sub.7OCH.sub.3 200 34 -123 -- 4.9 0 R-728 Nitrogen
(non-HFC) N.sub.2 28 -196 -210 A1 .infin. 0 R-740 Argon (non-HFC)
Ar 40 -186 -189 A1 .infin. 0 R-784 Krypton (non-HFC) Kr -- Xenon
(non-HFC) Xe R-744 Carbon dioxide (non-HFC) CO.sub.2 44 -57 -78 A1
33,000 1
[0061] According to embodiments described herein, the particular
selection of fluorocarbons for a mixed refrigerant depends on the
desired refrigeration temperatures. Natural gas liquefies to form
LNG at -162.degree. C. Therefore, in order to produce LNG, a mixed
refrigerant that is capable of chilling natural gas below
-162.degree. C. may be selected. In some cases, refrigerants may be
used at warmer temperatures, and another refrigeration process,
such as an autorefrigeration process, may be used to aid in the
production of LNG.
[0062] When selecting a set of fluorocarbons for a mixed
refrigerant, the normal boiling point and the melting point may
both be taken into consideration. It may be desirable for the
temperature of the mixed refrigerant to be above its freezing point
during the entire refrigeration cycle, so that the refrigerant will
not form solids and cause plugging in the system. In addition, it
may be desirable to be above atmospheric pressure during the entire
refrigeration cycle to avoid air contamination of the mixed
refrigerant. In various embodiments, the components of the mixed
refrigerant are selected such that the melting point of each
component is below the chilling temperature. There may be some
degree of flexibility in the melting point of the components, since
a mixture does not start to freeze at the warmest pure component
melting point. Some melting point depression occurs when a high
melting point component is diluted in other, non-freezing
components and approaches the eutectic point. For example, R-245fa,
which has a melting point of -102.degree. C., can be used at lower
temperatures if it is at a sufficiently low concentration in the
mixed refrigerant.
[0063] The particular selection of fluorocarbons for a mixed
refrigerant may also depend on the specific type of refrigeration
system for which the mixed refrigerant is to be used. For
example,
[0064] SMR cycles may use mixed refrigerants including a mixture of
R-14, R-23, R-32, R-227ea, R-245fa, or the like. Other possible
refrigerant components for the mixed refrigerant include R-41,
R-218, R-1234yf, R-1234ze, R-152a, and the like. In general, the
components of a mixed refrigerant may be selected such that their
NBPs evenly cover the desired refrigeration range.
[0065] 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 mixture of
the refrigerants described herein.
Refrigeration Systems
[0066] Hydrocarbon systems and methods often include refrigeration
systems that utilize mechanical refrigeration, valve expansion,
turbine expansion, or the like. Mechanical refrigeration typically
includes compression systems and absorption systems, such as
ammonia absorption systems. Compression systems are used in the gas
processing industry for a variety of processes. For example,
compression systems may be used for chilling natural gas for NGL
extraction, chilling natural gas for hydrocarbon dew point control,
LPG production storage, condensation of reflux in deethanizers or
demethanizers, natural gas liquefaction to produce LNG, or the
like.
[0067] FIG. 1 is a process flow diagram of a single stage
refrigeration system 100. In various embodiments, the single stage
refrigeration system 100 uses a mixed fluorocarbon refrigerant. The
use of a mixed fluorocarbon refrigerant may allow the single stage
refrigeration system 100 to maintain high efficiency over a wide
range of temperatures. Further, in various embodiments, the single
stage refrigeration system 100 is implemented upstream of a
nitrogen refrigeration system or methane autorefrigeration system
including an NRU. Multiple single stage refrigeration systems 100
may also be implemented in series upstream of such a nitrogen
refrigeration system or methane autorefrigeration system.
[0068] The single stage refrigeration system 100 includes an
expansion device 102, a chiller 104, a compressor 106, a condenser
108, and an accumulator 110. The expansion device 102 may be an
expansion valve or a hydraulic expander, for example. A saturated
liquid refrigerant 112 may flow from the accumulator 110 to the
expansion device 102, and may expand across the expansion device
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.
[0069] 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 device 102 as the
saturated liquid refrigerant 112.
[0070] 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.
[0071] 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
fluorocarbon refrigerant, such as an azeotrope (R-5XX) or a
near-azeotrope (R-4XX). Further, in various embodiments, the two
stage refrigeration system 200 is implemented upstream of a
nitrogen refrigeration system or methane autorefrigeration system
including an NRU. Multiple two stage refrigeration systems 200 may
also be implemented in series upstream of such a nitrogen
refrigeration system or methane autorefrigeration system.
[0072] 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.
[0073] As shown in FIG. 2, the saturated liquid refrigerant 112
leaving the accumulator 110 may be expanded across the expansion
device 102 to an intermediate pressure at which vapor and liquid
may be separated. For example, as the saturated liquid refrigerant
112 flashes across the expansion device 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.
[0074] From the economizer 202, the liquid refrigerant 206 may be
isenthalpically expanded across a second expansion device 214. The
second expansion device 214 may be an expansion valve or a
hydraulic expander, for example. 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.
[0075] 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.
[0076] 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.
[0077] In some embodiments, the two stage refrigeration system 200
includes more than one economizer 202, as well as more than two
compressors 210 and 212. For example, the two stage refrigeration
system 200 may include two economizers and three compressors. In
general, if the refrigeration system 200 includes X number of
economizers, the refrigeration system 200 will include X +1 number
of compressors. Such a refrigeration system 200 with multiple
economizers may form part of a cascade refrigeration system.
[0078] 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 mixed fluorocarbon refrigerant. Further, in various
embodiments, the single stage refrigeration system 300 is
implemented upstream of a nitrogen refrigeration system or methane
autorefrigeration system including an NRU. Multiple single stage
refrigeration systems 300 may also be implemented in series
upstream of such a nitrogen refrigeration system or methane
autorefrigeration system.
[0079] As shown in FIG. 3, the saturated liquid refrigerant 112
leaving the accumulator 110 may be expanded across the expansion
device 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.
[0080] 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.
[0081] 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.
[0082] FIG. 4 is a process flow diagram of an LNG production system
400. As shown in FIG. 4, LNG 402 may be produced from a natural gas
stream 404 using a number of different refrigeration systems. As
shown in FIG. 4, a portion of the natural gas stream 404 may be
separated from the natural gas stream 404 prior to entry into the
LNG production system 400, and may be used as a fuel gas stream
406. The remaining natural gas stream 404 may be flowed into an
initial natural gas processing system 408. Within the natural gas
processing system 408, the natural gas stream 404 may be purified
and cooled. For example, the natural gas stream 404 may be cooled
using a first mixed fluorocarbon refrigerant 410, a second mixed
fluorocarbon refrigerant 412, and a high-pressure nitrogen
refrigerant 414. The cooling of the natural gas stream 404 may
result in the production of the LNG 402. In some embodiments, the
broader temperature range of a mixed refrigerant system will make
it possible to use a single mixed refrigerant for both the first
mixed fluorocarbon refrigerant 410 and the second mixed
fluorocarbon refrigerant 412.
[0083] Within the LNG production system 400, heavy hydrocarbons 416
may be removed from the natural gas stream 406, and a portion of
the heavy hydrocarbons 416 may be used to produce gasoline 418
within a heavy hydrocarbon processing system 420. In addition, any
residual natural gas 422 that is separated from the heavy
hydrocarbons 416 during the production of the gasoline 418 may be
returned to the natural gas stream 404.
[0084] The produced LNG 402 may include some amount of nitrogen
424. Therefore, the LNG 402 may be flowed through an NRU 426. The
NRU 426 separates the nitrogen 424 from the LNG 402, producing the
final LNG product.
[0085] It is to be understood that the process flow diagram of FIG.
4 is not intended to indicate that the LNG production system 400 is
to include all the components shown in FIG. 4. Further, the LNG
production system 400 may include any number of additional
components not shown in FIG. 4 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 402 from the natural gas stream 404. In addition, any
number of different refrigeration systems may be used in
combination to produce the LNG 402.
Hydrocarbon Processing Systems for the Production of LNG
[0086] According to embodiments described herein, LNG may be
produced within a hydrocarbon processing system using mixed
fluorocarbon refrigerants. In some embodiments, the fluorocarbon
components within the mixed fluorocarbon refrigerants are
non-flammable, non-toxic, and non-reactive. The fluorocarbon
components for a particular mixed fluorocarbon refrigerant may be
selected such that the cooling curve of the mixed fluorocarbon
refrigerant closely matches the cooling curve of the LNG being
chilled. Matching the cooling curve of the mixed fluorocarbon
refrigerant to the cooling curve of the LNG may increase the
performance and efficiency of the hydrocarbon processing
system.
[0087] FIG. 5 is a process flow diagram of a hydrocarbon processing
system 500 including an SMR cycle 502. The SMR cycle 502 may cool a
feed gas 504 to produce LNG 506 using a mixed fluorocarbon
refrigerant 508. The hydrocarbon processing system 500 also
includes a low pressure NRU 510, which may be used to purify the
LNG 506 by separating the LNG 506 from a fuel stream 512 including
nitrogen.
[0088] The SMR cycle 502 includes a heat exchanger 514, a
compressor 516, a condenser 518, and an expansion device 520. The
expansion device 520 may be an expansion valve or a hydraulic
expander, for example. The mixed fluorocarbon refrigerant 508 is
flowed from the condenser 518 to the heat exchanger 514. Within the
heat exchanger 514, the mixed fluorocarbon refrigerant 508 cools
the feed gas 504 to produce the LNG 506 via indirect heat
exchange.
[0089] From the heat exchanger 514, the mixed fluorocarbon
refrigerant 508 is flowed to the expansion device 520, and is
expanded across the expansion device 520 isenthalpically. On
expansion, some vaporization occurs, creating a chilled mixed
fluorocarbon refrigerant 522 that includes both vapor and liquid.
The chilled mixed fluorocarbon refrigerant 522 is flowed back to
the heat exchanger 514 and is used to aid in the cooling of the
feed gas 508 within the heat exchanger 514. As the feed gas 508
exchanges heat with the chilled mixed fluorocarbon refrigerant 522,
the chilled mixed fluorocarbon refrigerant 522 vaporizes, creating
a vapor mixed fluorocarbon refrigerant 524.
[0090] The vapor mixed fluorocarbon refrigerant 524 is then
compressed within the compressor 516 and flowed into the condenser
518. Within the condenser 518, the vapor mixed fluorocarbon
refrigerant 524 is converted to a saturated, or slightly
sub-cooled, liquid mixed fluorocarbon refrigerant 508. The liquid
mixed fluorocarbon refrigerant 508 is then flowed back into the
heat exchanger 514.
[0091] In various embodiments, the LNG 506 that is produced via the
SMR cycle 502 includes some amount of impurities, such as nitrogen.
Therefore, the LNG 506 is flowed to into the NRU 510. The NRU 510
separates the fuel stream 512 including the nitrogen from the LNG
506, producing the final LNG product. The final LNG product may
then be flowed from the hydrocarbon processing system 500 to a
desired destination using a pump 526.
[0092] It is to be understood that the process flow diagram of FIG.
5 is not intended to indicate that the hydrocarbon processing
system 500 is to include all the components shown in FIG. 5.
Further, the hydrocarbon processing system 500 may include any
number of additional components not shown in FIG. 5, depending on
the details of the specific implementation.
[0093] FIG. 6 is a process flow diagram of the hydrocarbon
processing system 500 of FIG. 5 with the addition of a nitrogen
refrigeration system 600. Like numbered items are as described with
respect to FIG. 5. According to the embodiment shown in FIG. 6, the
SMR cycle 502 may be operated at a higher temperature. Therefore,
the output of the SMR cycle 502 may be cooled feed gas 504, rather
than LNG 506, or may be a mixture of cooled feed gas 504 and LNG
506.
[0094] From the SMR cycle 502, the feed gas 504 is flowed into the
nitrogen refrigeration system 600. Within the nitrogen
refrigeration system 600, the feed gas may be cooled to produce the
LNG 506 via indirect heat exchange with a nitrogen refrigerant 602
within a first heat exchanger 604. The LNG 506 is then flowed into
the NRU 510, as discussed with respect to FIG. 5.
[0095] The nitrogen refrigeration system 600 includes the first
heat exchanger 604, a second heat exchanger 606, a compressor 608,
a condenser 610, and an expander 612. From the first heat exchanger
604, the nitrogen refrigerant 602 is flowed through the second heat
exchanger 606. Within the second heat exchanger 606, the nitrogen
refrigerant 602 is cooled via indirect heat exchange with a
chilled, vapor nitrogen refrigerant 614. The nitrogen refrigerant
602 is then compressed within the compressor 608 and flowed into
the condenser 610.
[0096] Within the condenser 610, the nitrogen refrigerant 602 is
converted to the vapor nitrogen refrigerant 614. The vapor nitrogen
refrigerant 614 is flowed through the second heat exchanger 606, in
which the vapor nitrogen refrigerant 614 exchanges heat with the
warmer nitrogen refrigerant 602 exiting the first heat exchanger
604.
[0097] The chilled, vapor nitrogen refrigerant 614 is then flowed
through the expander 612. The expander 612 expands the vapor
nitrogen refrigerant 614 to a low pressure with a corresponding
reduction in temperature. The resulting cold nitrogen refrigerant
602 is flowed through the first heat exchanger 604 to exchange heat
with the feed gas 504.
[0098] It is to be understood that the process flow diagram of FIG.
6 is not intended to indicate that the hydrocarbon processing
system 600 is to include all the components shown in FIG. 6.
Further, the hydrocarbon processing system 600 may include any
number of additional components not shown in FIG. 6, depending on
the details of the specific implementation.
[0099] FIG. 7 is a process flow diagram of the hydrocarbon
processing system 500 of FIG. 5 with the addition of a methane
autorefrigeration system 700. Like numbered items are as described
with respect to FIG. 5. According to the embodiment shown in FIG.
7, the SMR cycle 502 may be operated at a higher temperature.
Therefore, the output of the SMR cycle 502 may be cooled feed gas
504, rather than LNG 506, or may be a mixture of cooled feed gas
504 and LNG 506.
[0100] From the SMR cycle 502, the cooled feed gas 504 is flowed
into the NRU 510. The NRU 510 purifies the feed gas 504, producing
an LNG bottoms stream 702 and a fuel gas overhead stream 704. The
LNG bottoms stream 702 is flowed through an expansion device 706,
such as an expansion valve or hydraulic expander, and into a heat
exchanger 708. Within the heat exchanger 708, the LNG bottoms
stream 702 exchanges heat with the overhead fuel stream 704,
cooling the overhead fuel stream 704 and producing a mixed fuel
stream 710 including both the vapor fuel stream 512 and a liquid
fuel stream 712.
[0101] The mixed fuel stream 710 is then flowed into a flash drum
714. The flash drum 714 separates the vapor fuel stream 512 from
the liquid fuel stream 712. The liquid fuel stream 712 may then be
flowed back into the NRU 510 as reflux.
[0102] As the LNG bottoms stream 702 exchanges heat with the
overhead fuel stream 704 within the heat exchanger 708, it may be
partially vaporized, producing a mixed phase feed stream 716. From
the heat exchanger 708, the mixed phase feed stream 716 is flowed
into a first flash drum 718 within the methane autorefrigeration
system 700.
[0103] The first flash drum 718 separates the mixed phase feed
stream 716 into a vapor stream 720 that includes primarily natural
gas and an LNG stream 722. The vapor stream 720 is flowed into a
first compressor 724. From the first compressor 724, the resulting
natural gas stream 726 may be combined with the initial feed gas
504 prior to entry of the feed gas 504 into the SMR cycle 502.
[0104] From the first flash drum 718, the LNG stream 722 is flowed
through an expansion device 728, such as an expansion valve or
hydraulic expander, which may control the flow of the LNG stream
728 into a second flash drum 730. Specifically, the expansion
device 728 may allow a portion of the liquid from the LNG stream
722 to flash, creating a mixed phase stream that is flowed into the
second flash drum 730.
[0105] The second flash drum 730 separates the mixed phase stream
into the final LNG product 506 and a vapor stream 732 that includes
primarily natural gas. The vapor stream 732 is flowed into a second
compressor 734. From the second compressor 734, the vapor stream
732 is combined with the vapor stream 720 from the first flash drum
718 prior to entry of the vapor stream 720 into the first
compressor 724. Furthermore, from the second flash drum 730, the
final LNG product 506 may be flowed to a desired destination using
the pump 526.
[0106] It is to be understood that the process flow diagram of FIG.
7 is not intended to indicate that the hydrocarbon processing
system 700 is to include all the components shown in FIG. 7.
Further, the hydrocarbon processing system 700 may include any
number of additional components not shown in FIG. 7, depending on
the details of the specific implementation.
[0107] FIG. 8 is a process flow diagram of a hydrocarbon processing
system 800 including a pre-cooled SMR cycle 802. The pre-cooled SMR
cycle 802 may cool a feed gas 804 to produce LNG 806 using a mixed
fluorocarbon refrigerant 808. The hydrocarbon processing system 800
also includes a low pressure NRU 810, which may be used to purify
the LNG 806 by separating the LNG 806 from a fuel stream 812
including nitrogen.
[0108] Within the pre-cooled SMR cycle 802, the incoming feed gas
804 is pre-cooled and partially condensed in a first chiller 814
via indirect heat exchange with a fluorocarbon refrigerant. For
example, the feed gas 804 may be cooled in the first chiller 814
using a refrigerant blend such as R-410a or R-404a, or using a pure
component refrigerant such as R-125, R-32, or R-218.
[0109] The chilled feed gas 816 is then flowed into a main
cryogenic heat exchanger 818. Within the main cryogenic heat
exchanger 818, the feed gas 816 is cooled to produce the LNG 806
via indirect heat exchange with the mixed fluorocarbon refrigerant
808. The main cryogenic heat exchanger 818 may include a number of
small-diameter, spiral-wound tube bundles 820, which may permit
very close temperature matches between the chilled feed gas 816 and
the mixed fluorocarbon refrigerant 808.
[0110] After the mixed fluorocarbon refrigerant 808 flows through
the main cryogenic heat exchanger 818, the mixed fluorocarbon
refrigerant 808 is expanded across an expansion device 822, such as
an expansion valve or hydraulic expander. On expansion, some
vaporization occurs, creating a chilled mixed fluorocarbon
refrigerant 824 that includes both vapor and liquid. The chilled
mixed fluorocarbon refrigerant 824 is then sprayed into the main
cryogenic heat exchanger 818 via a number of spray nozzles 826. In
various embodiments, spraying the chilled mixed fluorocarbon
refrigerant 824 into the main cryogenic heat exchanger 818 provides
for additional cooling of the feed gas 816 and the mixed
fluorocarbon refrigerant 808 flowing through the tube bundles
820.
[0111] The chilled mixed fluorocarbon refrigerant 824 is then
flowed out of the main cryogenic heat exchanger 818 as a bottoms
stream 828. The bottoms stream 828 is compressed in a compressor
830, producing a compressed mixed fluorocarbon refrigerant 832. The
compressed mixed fluorocarbon refrigerant 832 is chilled and
partially condensed within a second chiller 834 and a third chiller
836. The resulting chilled mixed fluorocarbon refrigerant 838 is
flowed into a flash drum 839, which separates the chilled mixed
fluorocarbon refrigerant 838 into a vapor stream and a liquid
stream. The vapor stream is flowed into the main cryogenic heat
exchanger 818 as the mixed fluorocarbon refrigerant 808, and the
liquid stream is flowed into the main cryogenic heat exchanger 818
as an additional mixed fluorocarbon refrigerant 840. The additional
mixed fluorocarbon refrigerant 840 may provide cooling for the
mixed fluorocarbon refrigerant 808 via indirect heat exchange with
the mixed fluorocarbon refrigerant 808.
[0112] Upon exiting the main cryogenic heat exchanger 818, the
additional mixed fluorocarbon refrigerant 840 is expanded across an
expansion device 842, such as an expansion valve or hydraulic
expander. On expansion, some vaporization occurs, creating a
chilled mixed fluorocarbon refrigerant 844 that includes both vapor
and liquid. The chilled mixed fluorocarbon refrigerant 844 is then
sprayed into the main cryogenic heat exchanger 818 via a number of
additional spray nozzles 846. After flowing through the main
cryogenic heat exchanger 818, the chilled mixed fluorocarbon
refrigerant 844 is flowed out of the main cryogenic heat exchanger
818 along with the bottoms stream 828.
[0113] From the main cryogenic heat exchanger 818, the produced LNG
806 is flowed through an expansion device 848, such as an expansion
valve or hydraulic expander, and into the NRU 810. The NRU 810
separates the fuel stream 812 from the LNG 806, producing the final
LNG product. The final LNG product may then be flowed from the
hydrocarbon processing system 800 to a desired destination using a
pump 850.
[0114] It is to be understood that the process flow diagram of FIG.
8 is not intended to indicate that the hydrocarbon processing
system 800 is to include all the components shown in FIG. 8.
Further, the hydrocarbon processing system 800 may include any
number of additional components not shown in FIG. 8, depending on
the details of the specific implementation. In some embodiments,
the mixed fluorocarbon refrigerant 808 used in the main cryogenic
heat exchanger 818 of FIG. 8 includes nitrogen, e.g., R-728, and/or
argon, e.g., R-740, in addition to one or more fluorocarbon
refrigerant components.
[0115] FIG. 9 is a process flow diagram of a hydrocarbon processing
system 900 including a DMR cycle 902. The DMR cycle 902 may include
a warm MR cycle and a cold MR cycle connected in series. The DMR
cycle 902 may be used to cool a feed gas 904 to produce LNG 906
using a first mixed fluorocarbon refrigerant 908 within the warm MR
cycle and a second mixed fluorocarbon refrigerant 910 within the
cold MR cycle. The hydrocarbon processing system 900 also includes
a low pressure NRU 912, which may be used to purify the LNG 906 by
separating the LNG 906 from a fuel stream 914 including
nitrogen.
[0116] In some embodiments, the first mixed fluorocarbon
refrigerant 908 within the warm MR cycle includes R-32, R-152a,
R-245fa, R-227ea, HFE-347mcc, and/or other high boiling components.
In addition, in some embodiments, the second mixed fluorocarbon
refrigerant 910 within the cold MR cycle includes R-14, R-170,
R-41, xenon, R-23, R-116, R-1150, R-50, R-784, and/or other low
boiling components.
[0117] Within the hydrocarbon processing system 900, the feed gas
904 is cooled to produce the LNG 906 using a first heat exchanger
916 and a second heat exchanger 918. The feed gas 904 is cooled
within the first heat exchanger 916 via indirect heat exchange
along with the first mixed fluorocarbon refrigerant 908 and the
second mixed fluorocarbon refrigerant 910.
[0118] From the first heat exchanger 916, the first mixed
fluorocarbon refrigerant 908 is flowed to an expansion device 920,
such as an expansion valve or hydraulic expander, and is expanded
across the expansion device 920 isenthalpically. On expansion, some
vaporization occurs, creating a chilled mixed fluorocarbon
refrigerant 922 that includes both vapor and liquid. The chilled
mixed fluorocarbon refrigerant 922 is flowed back to the first heat
exchanger 916 and is used to cool the first mixed fluorocarbon
refrigerant 908, the second mixed fluorocarbon refrigerant 910, and
the feed gas 904 within the first heat exchanger 916. As the first
mixed fluorocarbon refrigerant 908, the second mixed fluorocarbon
refrigerant 910, and the feed gas 904 exchange heat with the
chilled mixed fluorocarbon refrigerant 922, the chilled mixed
fluorocarbon refrigerant 922 vaporizes, creating a vapor mixed
fluorocarbon refrigerant 924.
[0119] The vapor mixed fluorocarbon refrigerant 924 is then
compressed within a compressor 926 and condensed within a condenser
928. The condensed mixed fluorocarbon refrigerant is then flowed
back into the first heat exchanger 916 as the first mixed
fluorocarbon refrigerant 908.
[0120] From the first heat exchanger 916, the second mixed
fluorocarbon refrigerant 910 is flowed into the second heat
exchanger 918. Within the second heat exchanger 918, the second
mixed fluorocarbon refrigerant 910 is further cooled along with the
feed gas 904, producing the LNG 906.
[0121] Upon exiting the second heat exchanger 918, the second mixed
fluorocarbon refrigerant 910 is flowed to an expansion device 930,
such as an expansion valve or hydraulic expander, and is expanded
across the expansion device 930 isenthalpically. On expansion, some
vaporization occurs, creating a chilled mixed fluorocarbon
refrigerant 932 that includes both vapor and liquid. The chilled
mixed fluorocarbon refrigerant 932 is flowed back to the second
heat exchanger 918 and is used to cool both the feed gas 904 and
the second mixed fluorocarbon refrigerant 910 within the second
heat exchanger 918. As the feed gas 904 exchanges heat with the
chilled mixed fluorocarbon refrigerant 932, the chilled mixed
fluorocarbon refrigerant 932 vaporizes, creating a vapor mixed
fluorocarbon refrigerant 934.
[0122] The vapor mixed fluorocarbon refrigerant 934 is then
compressed within a compressor 936, and cooled within a heat
exchanger 938. The condensed mixed fluorocarbon refrigerant is
flowed back into the first heat exchanger 916 as the second mixed
fluorocarbon refrigerant 910.
[0123] In various embodiments, the LNG 906 that is produced via the
DMR cycle 902 includes some amount of impurities, such as nitrogen.
Therefore, the LNG 906 is flowed to into the NRU 912. The NRU 912
separates the fuel stream 914 from the LNG 906, producing the final
LNG product. The final LNG product may be flowed from the
hydrocarbon processing system 900 to a desired destination using a
pump 940.
[0124] It is to be understood that the process flow diagram of FIG.
9 is not intended to indicate that the hydrocarbon processing
system 900 is to include all the components shown in FIG. 9.
Further, the hydrocarbon processing system 900 may include any
number of additional components not shown in FIG. 9, depending on
the details of the specific implementation.
[0125] FIGS. 10A and 10B are process flow diagrams of a hydrocarbon
processing system 1000 including an SMR cycle 1002, an NRU 1004,
and a methane autorefrigeration system 1006. In various
embodiments, the hydrocarbon processing system 1000 is used to
produce LNG 1008 from a natural gas stream 1010.
[0126] As shown in FIG. 10A, the natural gas stream 1010 is flowed
into a pipe joint 1012 within the hydrocarbon processing system
1000. The pipe joint 1012 combines the natural gas stream 1010 with
another natural gas stream. The combined natural gas stream is
compressed within a first compressor 1014 and flowed into another
pipe joint 1016 via line 1018.
[0127] The pipe joint 1016 splits the natural gas stream into two
separate natural gas streams. A first natural gas stream is
combined with another natural gas stream via a pipe joint 1020 and
then flowed out of the hydrocarbon processing system 1000 as fuel
1022. A second natural gas stream is chilled within a first chiller
1024 and flowed into another pipe joint 1026. The pipe joint 1026
splits the natural gas stream into two separate natural gas
streams. A first natural gas stream is flowed into a first heat
exchanger 1028 within the SMR cycle 1002 via line 1030. A second
natural gas stream is flowed into a second heat exchanger 1032 via
line 1034.
[0128] Within the first heat exchanger 1028, the natural gas stream
is cooled via indirect heat exchange with a circulating mixed
fluorocarbon refrigerant stream. From the first heat exchanger
1028, the mixed fluorocarbon refrigerant stream is flowed to an
expansion device 1036, such as an expansion valve or hydraulic
expander, via line 1038, and is expanded across the expansion
device 1036 isenthalpically. On expansion, some vaporization
occurs, creating a chilled mixed fluorocarbon refrigerant stream
that includes both vapor and liquid. The chilled mixed fluorocarbon
refrigerant stream is flowed back to the first heat exchanger 1028
and is used to aid in the cooling of the natural gas stream within
the first heat exchanger 1028. As the natural gas stream exchanges
heat with the chilled mixed fluorocarbon refrigerant stream, the
chilled mixed fluorocarbon refrigerant stream vaporizes, creating a
vapor mixed fluorocarbon refrigerant stream.
[0129] The vapor mixed fluorocarbon refrigerant is then compressed
within a second compressor 1040 and partially condensed within a
second chiller 1042. The condensed mixed fluorocarbon refrigerant
is then flowed into a first flash drum 1044 via line 1046. The
flash drum separates the partially condensed mixed fluorocarbon
refrigerant stream into a vapor mixed fluorocarbon refrigerant
stream and a liquid mixed fluorocarbon refrigerant. The vapor mixed
fluorocarbon refrigerant stream is compressed within a third
compressor 1048 and flowed into a pipe joint 1050. The liquid mixed
fluorocarbon refrigerant stream is pumped into the pipe joint 1050
via a pump 1052.
[0130] Within the pipe joint 1050, the vapor and liquid mixed
fluorocarbon refrigerant streams are recombined. The recombined
mixed fluorocarbon refrigerant stream is further cooled within a
third chiller 1053 and flowed back into the first heat exchanger
1028. Within the first heat exchanger 1028, the recombined mixed
fluorocarbon refrigerant stream is fully condensed and sub-cooled,
and is then flowed back to the expansion device 1036 via line
1038.
[0131] From the first heat exchanger 1028, the resulting LNG stream
is flowed into a pipe joint 1054, in which it is combined with an
LNG stream from the second heat exchanger 1032. The combined LNG
stream is then flowed into the NRU 1004 via line 1056 to remove
excess nitrogen from the LNG stream. Specifically, the LNG stream
is flowed into a reboiler 1058, which decreases the temperature of
the LNG stream. The cooled LNG stream may be expanded within a
hydraulic expansion turbine 1060 and flowed through an expansion
device 1062, such as an expansion valve or hydraulic expander,
which lowers the temperature and pressure of the LNG stream.
[0132] The LNG stream is flowed into a cryogenic fractionation
column 1064, such as an NRU tower, within the NRU 1004. In
addition, heat is transferred to the cryogenic fractionation column
1064 from the reboiler 1058 via line 1066. The cryogenic
fractionation column 1064 separates nitrogen from the LNG stream
via a cryogenic distillation process. An overhead stream is flowed
out of the cryogenic fractionation column 1064 via line 1068. 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.
[0133] The overhead stream is flowed into a reflux condenser 1070
via line 1068. Within the reflux condenser 1070, the overhead
stream is cooled via indirect heat exchange with an LNG stream. The
heated overhead stream is then flowed into a reflux separator 1072.
The reflux separator 1072 separates any liquid within the overhead
stream and returns the liquid to the cryogenic fractionation column
1064 as reflux. The separation of the liquid from the overhead
stream via the reflux separator 1072 results in the production of a
vapor stream. The vapor stream may be a fuel stream including
primarily nitrogen and other low boiling point gases. From the
reflux separator 1072, the vapor stream is flowed through the
second heat exchanger 1032 via line 1074. The vapor stream is
compressed within a fourth compressor 1076, chilled within a fourth
chiller 1078, further compressed within a fifth compressor 180, and
further chilled within a fifth chiller 1082. The fuel stream is
then combined with the other natural gas stream within the pipe
joint 1020 and flowed out of the hydrocarbon processing system 1000
as fuel 1022.
[0134] The bottoms stream that is produced within the cryogenic
fractionation column 1064 includes primarily LNG with traces of
nitrogen. The LNG stream is flowed into the reflux condenser 1070
and is used to cool the overhead stream from the cryogenic
fractionation column 1064. As the LNG stream exchanges heat with
overhead stream, it is partially vaporized, producing a multiphase
natural gas stream.
[0135] The multiphase natural gas stream is flowed into a second
flash drum 1084 via line 1083. The second flash drum 1084 separates
the multiphase natural gas stream into a natural gas stream and an
LNG stream. The natural gas stream is combined within another
natural gas stream within a pipe joint 1086, compressed within a
sixth compressor 1087, and combined with the initial natural gas
stream 1010 within the pipe joint 1012.
[0136] From the second flash drum 1084, the LNG stream is flowed
through an expansion device 1088, such as an expansion valve or
hydraulic expander, that controls the flow of the natural gas
stream into a third flash drum 1089. The expansion device 1088
reduces the temperature and pressure of the natural gas stream,
resulting in the flash evaporation of the natural gas stream into
both a natural gas stream and an LNG stream. The natural gas stream
is then separated from the LNG steam via the third flash drum
1089.
[0137] The natural gas stream is flowed from the third flash drum
1089 into a pipe joint 1090, in which the natural gas stream is
combined with another natural gas stream. The combined natural gas
stream is compressed within a seventh compressor 1091 and then
flowed into the pipe joint 1086.
[0138] From the third flash drum 1089, the LNG stream is flowed
through an expansion device 1092, such as an expansion valve or
hydraulic expander, that controls the flow of the natural gas
stream into a fourth flash drum 1093. The expansion device 1092
reduces the temperature and pressure of the natural gas stream,
resulting in the flash evaporation of the natural gas stream into
both a natural gas stream and an LNG stream. The natural gas stream
is then separated from the LNG steam via the fourth flash drum
1093.
[0139] The natural gas stream is flowed from the fourth flash drum
1093 into a pipe joint 1094, in which the natural gas stream is
combined with another natural gas stream. The combined natural gas
stream is compressed within an eighth compressor 1095 and flowed
into the pipe joint 1090.
[0140] The LNG stream is flowed into an LNG tank 1096. The LNG tank
1096 may store the LNG stream for any period of time. Boil-off gas
generated within the LNG tank 1096 is flowed to the pipe joint 1094
and combined within the natural gas stream from the fourth flash
drum 1093. At any point in time, the final LNG stream 1008 may be
transported to a LNG tanker 1097 using a pump 1098, for transport
to markets. Additional boil-off gas 1099 generated while loading
the final LNG stream 1008 into the LNG tanker 1097 may be recovered
in the hydrocarbon processing system 1000.
[0141] It is to be understood that the process flow diagrams of
FIGS. 10A and 10B are not intended to indicate that the hydrocarbon
processing system 1000 is to include all the components shown in
FIGS. 10A and 10B. Further, the hydrocarbon processing system 1000
may include any number of additional components not shown in FIGS.
10A and 10B, depending on the details of the specific
implementation.
[0142] FIGS. 11A and 11B are process flow diagrams of a hydrocarbon
processing system 1100 including an economized DMR cycle 1102, an
NRU 1104, and a methane autorefrigeration system 1106. In various
embodiments, the hydrocarbon processing system 1100 is used to
produce LNG 1108 from a natural gas stream 1110.
[0143] As shown in FIG. 11A, the natural gas stream 1110 is flowed
into a pipe joint 1112 within the hydrocarbon processing system
1100. The pipe joint 1112 splits the natural gas stream 110 into
three separate natural gas streams. A first natural gas stream is
flowed to a pipe joint 1114 via line 1116. Within the pipe joint
1114, the first natural gas stream is combined with another stream
including natural gas, and the combined stream is flowed out of the
hydrocarbon processing system 1100 as fuel 1118.
[0144] From the pipe joint 1112, a second natural gas stream is
flowed into the NRU 1104. Within the NRU 1104, the natural gas
stream is cooled within a first heat exchanger 1120 and combined
with an LNG stream exiting the economized DMR cycle 1102 within a
pipe joint 1122.
[0145] Furthermore, a third natural gas stream is flowed from the
pipe joint 1112 to another pipe joint 1124 as the main feed stream.
Within the pipe joint 1124, the natural gas stream is combined with
another natural gas stream from the methane autorefrigeration
system 1106. The combined natural gas stream is then cooled within
the economized DMR cycle 1102. Specifically, the natural gas stream
is cooled using a second heat exchanger 1126, a third heat
exchanger 1128, and a fourth heat exchanger 1130 within a warm MR
cycle of the economized DMR cycle 1102. The natural gas stream is
further cooled using a fifth heat exchanger 1132 and a sixth heat
exchanger 1134 within a cold MR cycle of the economized DMR cycle
1102.
[0146] Within the second heat exchanger 1126, the natural gas
stream is cooled via indirect heat exchange with a circulating warm
fluorocarbon refrigerant stream. From the second heat exchanger
1126, the warm fluorocarbon refrigerant stream is flowed into a
pipe joint 1140, in which it is combined with another warm
fluorocarbon refrigerant stream from the third and fourth heat
exchangers 1128 and 1130.
[0147] From the pipe joint 1140, the warm fluorocarbon refrigerant
stream is compressed within a compressor 1142 and chilled within a
chiller 1144. The warm fluorocarbon refrigerant stream is then
flowed through the second heat exchanger 1126. Within the second
heat exchanger 1126, the warm fluorocarbon refrigerant stream is
sub-cooled via indirect heat exchange. From the second heat
exchanger 1126, the sub-cooled fluorocarbon refrigerant stream is
flowed to a pipe joint 1148, which splits the fluorocarbon
refrigerant stream into two fluorocarbon refrigerant streams. A
first fluorocarbon refrigerant stream is flowed through an
expansion device 1150 and back into the second heat exchanger 1126.
Within the second heat exchanger 1126, the fluorocarbon refrigerant
stream cools the natural gas stream and the other fluorocarbon
refrigerant streams flowing through the second heat exchanger 1126.
The fluorocarbon refrigerant stream is then flowed into the pipe
joint 1140.
[0148] A second fluorocarbon refrigerant stream is flowed from the
pipe joint 1150 into the third heat exchanger 1128 via line 1152.
Within the third heat exchanger 1128, the fluorocarbon refrigerant
stream is further chilled and sub-cooled via indirect heat
exchange. From the third heat exchanger 1128, the sub-cooled
fluorocarbon refrigerant stream is flowed to a pipe joint 1153,
which splits the fluorocarbon refrigerant stream into two
fluorocarbon refrigerant streams. A first fluorocarbon refrigerant
stream is flowed through an expansion device 1154 and back into the
third heat exchanger 1128. Within the third heat exchanger 1128,
the fluorocarbon refrigerant stream cools the natural gas stream
and the other fluorocarbon refrigerant streams flowing through the
third heat exchanger 1128. The fluorocarbon refrigerant stream is
then flowed into a pipe joint 1156, in which it is combined with
another warm fluorocarbon refrigerant stream from the fourth heat
exchanger 1130. From the pipe joint 1156, the combined warm
fluorocarbon refrigerant stream is compressed within a compressor
1158, chilled within a chiller 1159, and flowed into the pipe joint
1140 to be combined with the fluorocarbon refrigerant stream
exiting the second heat exchanger 1126.
[0149] A second fluorocarbon refrigerant stream is flowed from the
pipe joint 1153 into the fourth heat exchanger 1130 via line 1160.
Within the fourth heat exchanger 1130, the fluorocarbon refrigerant
stream is further chilled and sub-cooled via indirect heat
exchange. From the fourth heat exchanger 1130, the sub-cooled
fluorocarbon refrigerant stream is flowed through an expansion
device 1161 and back into the fourth heat exchanger 1130. Within
the fourth heat exchanger 1130, the fluorocarbon refrigerant stream
cools the natural gas stream and the other fluorocarbon refrigerant
streams flowing through the fourth heat exchanger 1130. The
fluorocarbon refrigerant stream is then compressed within a
compressor 1163 and flowed into the pipe joint 1156 to be combined
with the fluorocarbon refrigerant stream exiting the third heat
exchanger 1128.
[0150] In various embodiments, a fluorocarbon refrigerant stream
from the cold MR cycle of the economized DMR cycle 1102 is flowed
through the second heat exchanger 1126, the third heat exchanger
1128, and the fourth heat exchanger 1130 within the warm MR cycle
via line 1164. Within the second heat exchanger 1126, the third
heat exchanger 1128, and the fourth heat exchanger 1130, the
fluorocarbon refrigerant stream from the cold MR cycle is cooled
and condensed via indirect heat exchange with the fluorocarbon
refrigerant within the warm MR cycle. The cold, liquid fluorocarbon
refrigerant stream exiting the fourth heat exchanger 1130 is flowed
into the fifth heat exchanger 1132 of the cold MR cycle via line
1165.
[0151] Within the fifth heat exchanger 1132, the cold fluorocarbon
refrigerant stream is further sub-cooled via indirect heat
exchange. From the fifth heat exchanger 1132, the sub-cooled
fluorocarbon refrigerant stream is flowed to a pipe joint 1166,
which splits the fluorocarbon refrigerant stream into two
fluorocarbon refrigerant streams. A first fluorocarbon refrigerant
stream is flowed through an expansion device 1167 and back into the
fifth heat exchanger 1132. Within the fifth heat exchanger 1132,
the fluorocarbon refrigerant stream cools the natural gas stream
and the incoming liquid fluorocarbon refrigerant stream 1165. The
fluorocarbon refrigerant stream is then flowed into a pipe joint
1168, in which it is combined with a fluorocarbon refrigerant
stream from the sixth heat exchanger 1134. The combined
fluorocarbon refrigerant stream is compressed within a compressor
1169, chilled within a chiller 1170, and flowed back into the warm
MR cycle of economized DMR cycle 1102 via line 1164.
[0152] A second fluorocarbon refrigerant stream is flowed from the
pipe joint 1166 into the sixth heat exchanger 1134 via line 1171.
Within the sixth heat exchanger 1134, the fluorocarbon refrigerant
stream is further chilled and sub-cooled via indirect heat
exchange. From the sixth heat exchanger 1134, the fluorocarbon
refrigerant stream is flowed through an expansion valve 1172 and
back into the sixth heat exchanger 1134. Within the sixth heat
exchanger 1134, the fluorocarbon refrigerant stream cools the
natural gas stream, producing an LNG stream, and chills the liquid
fluorocarbon refrigerant stream. The fluorocarbon refrigerant
stream is then compressed within a compressor 1173 and flowed into
the pipe joint 1168, in which it is combined with the fluorocarbon
refrigerant stream exiting the fifth heat exchanger 1132.
[0153] From the sixth heat exchanger 1134, the resulting LNG stream
is flowed out of the economized DMR cycle 1102 and into the NRU
1104 via line 1174. Specifically, the LNG stream is flowed into the
pipe joint 1122, in which it is combined with the natural gas
stream exiting the first heat exchanger 1120. The LNG stream is
then flowed into a reboiler 1175, which decreases the temperature
of the LNG stream. The cooled LNG stream may be expanded within a
hydraulic expansion turbine 1176 and flowed through an expansion
device 1177, such as an expansion valve or hydraulic expander,
which lowers the temperature and pressure of the LNG stream.
[0154] The LNG stream is flowed into a cryogenic fractionation
column 1178, such as an NRU tower, within the NRU 1104. In
addition, heat is transferred to the cryogenic fractionation column
1178 from the reboiler 1175 via line 1179. The cryogenic
fractionation column 1178 separates nitrogen from the LNG stream
via a cryogenic distillation process. An overhead stream is flowed
out of the cryogenic fractionation column 1178 via line 1180. 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.
[0155] The overhead stream is flowed into a reflux condenser 1181.
Within the reflux condenser 1181, the overhead stream is cooled via
indirect heat exchange with an LNG stream. The heated overhead
stream is then flowed into a reflux separator 1182. The reflux
separator 1182 separates any liquid within the overhead stream and
returns the liquid to the cryogenic fractionation column 1178 as
reflux. The separation of the liquid from the overhead stream via
the reflux separator 1182 results in the production of a vapor
stream. The vapor stream may be a fuel stream including primarily
nitrogen and other low boiling point gases. From the reflux
separator 1182, the vapor stream is flowed through the first heat
exchanger 1120. The vapor stream is then progressively compressed
and chilled within a first compressor 1183, a first chiller 1184, a
second compressor 1185, and a second chiller 1186. The compressed,
chilled stream is then combined with a natural gas stream within
the pipe joint 1114, and the combined stream is flowed out of the
hydrocarbon processing system 1100 as fuel 1118.
[0156] The bottoms stream that is produced within the cryogenic
fractionation column 1178 includes primarily LNG with traces of
nitrogen. The LNG is flowed through the reflux condenser 1181 and
is used to cool the overhead stream from the cryogenic
fractionation column 1178. As the LNG stream exchanges heat with
the overhead stream, it is partially vaporized, producing a
multiphase natural gas stream.
[0157] The multiphase natural gas stream is flowed into a third
flash drum 1187, which separates the multiphase natural gas stream
into a natural gas stream and an LNG stream. The natural gas stream
is combined within another natural gas stream within a pipe joint
1188, compressed within a compressor 1189, chilled within a chiller
1190, and combined with the initial natural gas stream within the
pipe joint 1124.
[0158] From the third flash drum 1187, the LNG stream is flowed
through an expansion device 1191, such as an expansion valve or
hydraulic expander, that controls the flow of the natural gas
stream into a fourth flash drum 1192. The expansion device 1191
reduces the temperature and pressure of the natural gas stream,
resulting in the flash evaporation of the natural gas stream into
both a natural gas stream and an LNG stream. The natural gas stream
is then separated from the LNG steam via the fourth flash drum
1192.
[0159] The natural gas stream is flowed from the fourth flash drum
1192 into a pipe joint 1193, in which the natural gas stream is
combined with another natural gas stream. The combined natural gas
stream is compressed within a compressor 1194 and then flowed into
the pipe joint 1188 to be combined with the natural gas stream from
the third flash drum 1187.
[0160] From the fourth flash drum 1192, the LNG stream is flowed
into an LNG tank 1195. The LNG tank 1195 may store the LNG stream
for any period of time. Boil-off gas generated within the LNG tank
1195 is flowed to the pipe joint 1193 and combined within the
natural gas stream from the fourth flash drum 1192. At any point in
time, the final LNG stream 1108 may be transported to a LNG tanker
1196 using a pump 1197, for transport to markets. Additional
boil-off gas 1198 generated while loading the final LNG stream 1108
into the LNG tanker 1196 may be recovered in the hydrocarbon
processing system 1100.
Method for LNG Production
[0161] FIG. 12 is a process flow diagram of a method 1200 for the
formation of LNG from a natural gas stream using a mixed
fluorocarbon refrigerant. The method 1200 may be implemented within
any suitable type of hydrocarbon processing system. For example,
the method 1200 may be implemented by any of the hydrocarbon
processing systems 500 or 800-1100 discussed with respect to FIGS.
5-11.
[0162] The method 1200 begins at block 1202, at which a natural gas
is cooled to produce LNG in a fluorocarbon refrigeration system
using a mixed fluorocarbon refrigerant. The mixed fluorocarbon
refrigerant may include any suitable mixture of fluorocarbon
components, or any suitable mixture of fluorocarbon components and
other non-flammable components, such as inert compounds. For
example, the mixed fluorocarbon refrigerant may be a mixture of any
number of different HFCs, HFOs, and/or inert compounds.
[0163] Cooling the natural gas in the fluorocarbon refrigeration
system may include compressing the mixed fluorocarbon refrigerant
to provide a compressed mixed fluorocarbon refrigerant and cooling
the compressed mixed fluorocarbon refrigerant by indirect heat
exchange with a cooling fluid to provide a cooled mixed
fluorocarbon refrigerant. The cooled mixed fluorocarbon refrigerant
may then be passed to a heat exchange area, and the natural gas may
be cooled by indirect heat exchange with the cooled mixed
fluorocarbon refrigerant in the heat exchange area.
[0164] The fluorocarbon refrigeration system may be any suitable
type of refrigeration system that is capable of cooling a natural
gas stream using a mixed fluorocarbon refrigerant. For example, the
fluorocarbon refrigeration system may be an SMR cycle, DMR cycle,
TMR cycle, or pre-cooled MR cycle. If the fluorocarbon
refrigeration system is a DMR cycle, for example, the fluorocarbon
refrigeration system may include a first MR cycle that uses a warm
mixed fluorocarbon refrigerant and a second MR cycle that uses a
cold mixed fluorocarbon refrigerant. The first mixed refrigerant
cycle and the second mixed refrigerant cycle may be connected in
series.
[0165] At block 1204, nitrogen is removed from the LNG in an NRU.
In some embodiments, the nitrogen stream separated from the natural
gas via the NRU is used to further cool at least a portion of the
natural gas.
[0166] In various embodiments, the natural gas is further cooled to
produce the LNG in an autorefrigeration system. The
autorefrigeration system may include a number of expansion devices
and flash drums for cooling the natural gas. In addition, in some
embodiments, the natural gas is further cooled to produce the LNG
in a nitrogen refrigeration system using a nitrogen refrigerant.
The nitrogen refrigeration system may be located upstream of the
autorefrigeration system, for example.
[0167] It is to be understood that the process flow diagram of FIG.
12 is not intended to indicate that the blocks of the method 1200
are to be executed in any particular order, or that all of the
blocks are to be included in every case. Further, any number of
additional blocks may be included within the method 1200, depending
on the details of the specific implementation.
Embodiments
[0168] Embodiments of the techniques 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.
[0169] 1. A hydrocarbon processing system for liquefied natural gas
(LNG) production, including: [0170] a fluorocarbon refrigeration
system configured to cool a natural gas to produce LNG using a
mixed fluorocarbon refrigerant; and [0171] a nitrogen rejection
unit (NRU) configured to remove nitrogen from the LNG.
[0172] 2. The hydrocarbon processing system of paragraph 1,
including a nitrogen refrigeration system configured to further
cool the natural gas to produce the LNG using a nitrogen
refrigerant.
[0173] 3. The hydrocarbon processing system of any of paragraphs 1
or 2, including an autorefrigeration system configured to further
cool the natural gas to produce the LNG.
[0174] 4. The hydrocarbon processing system of paragraph 3, wherein
the autorefrigeration system includes a number of flash drums and a
number of expansion devices.
[0175] 5. The hydrocarbon processing system of any of paragraphs
1-3, wherein at least a portion of the natural gas is cooled using
a nitrogen stream separated from the natural gas via the NRU.
[0176] 6. The hydrocarbon processing system of any of paragraphs
1-3 or 5, wherein the fluorocarbon refrigeration system includes a
single mixed refrigerant cycle.
[0177] 7. The hydrocarbon processing system of any of paragraphs
1-3, 5, or 6, wherein the fluorocarbon refrigeration system
includes a pre-cooled mixed refrigerant cycle.
[0178] 8. The hydrocarbon processing system of any of paragraphs
1-3 or 5-7, wherein the fluorocarbon refrigeration system includes
a dual mixed refrigerant cycle.
[0179] 9. The hydrocarbon processing system of paragraph 8, wherein
the dual mixed refrigerant cycle includes: [0180] a first mixed
refrigerant cycle that uses a warm mixed fluorocarbon refrigerant;
and [0181] a second mixed refrigerant cycle that uses a cold mixed
fluorocarbon refrigerant, wherein the first mixed refrigerant cycle
and the second mixed refrigerant cycle are connected in series.
[0182] 10. The hydrocarbon processing system of any of paragraphs
1-3 or 5-8, wherein the fluorocarbon refrigeration system includes
a triple mixed refrigerant cycle.
[0183] 11. The hydrocarbon processing system of any of paragraphs
1-3, 5-8, or 10, wherein the fluorocarbon refrigeration system
includes a heat exchanger configured to allow for cooling of the
natural gas via an indirect exchange of heat between the natural
gas and the mixed fluorocarbon refrigerant.
[0184] 12. The hydrocarbon processing system of any of paragraphs
1-3, 5-8, 10, or 11, wherein the fluorocarbon refrigeration system
includes:
[0185] a compressor configured to compress the mixed fluorocarbon
refrigerant to provide a compressed mixed fluorocarbon
refrigerant;
[0186] a chiller configured to cool the compressed mixed
fluorocarbon refrigerant to provide a cooled mixed fluorocarbon
refrigerant; and
[0187] a heat exchanger configured to cool the natural gas via
indirect heat exchange with the cooled mixed fluorocarbon
refrigerant.
[0188] 13. The hydrocarbon processing system of any of paragraphs
1-3, 5-8, or 10-12, wherein the hydrocarbon processing system is
configured to chill the natural gas for hydrocarbon dew point
control.
[0189] 14. The hydrocarbon processing system of any of paragraphs
1-3, 5-8, or 10-13, wherein the hydrocarbon processing system is
configured to chill the natural gas for natural gas liquid
extraction.
[0190] 15. The hydrocarbon processing system of any of paragraphs
1-3, 5-8, or 10-14, wherein the hydrocarbon processing system is
configured to separate methane and lighter gases from carbon
dioxide and heavier gases.
[0191] 16. The hydrocarbon processing system of any of paragraphs
1-3, 5-8, or 10-15, wherein the hydrocarbon processing system is
configured to prepare hydrocarbons for liquefied petroleum gas
production storage.
[0192] 17. The hydrocarbon processing system of any of paragraphs
1-3, 5-8, or 10-16, wherein the hydrocarbon processing system is
configured to condense a reflux stream.
[0193] 18. A method for liquefied natural gas (LNG) production,
including:
[0194] cooling a natural gas to produce LNG in a fluorocarbon
refrigeration system using a mixed fluorocarbon refrigerant; and
[0195] removing nitrogen from the LNG in a nitrogen rejection unit
(NRU).
[0196] 19. The method of any of paragraphs 18, including further
cooling the natural gas to produce the LNG in a nitrogen
refrigeration system using a nitrogen refrigerant.
[0197] 20. The method of any of paragraphs 18 or 19, including
further cooling the natural gas to produce the LNG in an
autorefrigeration system.
[0198] 21. The method of paragraph 20, including cooling at least a
portion of the natural gas using a nitrogen stream separated from
the natural gas via the NRU.
[0199] 22. The method of any of paragraphs 18-20, wherein cooling
the natural gas in the fluorocarbon refrigeration system includes:
[0200] compressing the mixed fluorocarbon refrigerant to provide a
compressed mixed fluorocarbon refrigerant; [0201] cooling the
compressed mixed fluorocarbon refrigerant by indirect heat exchange
with a cooling fluid to provide a cooled mixed fluorocarbon
refrigerant; [0202] passing the cooled mixed fluorocarbon
refrigerant to a heat exchange area; and heat exchanging the
natural gas with the cooled mixed fluorocarbon refrigerant in the
heat exchange area.
[0203] 23. A hydrocarbon processing system for formation of a
liquefied natural gas (LNG), including: [0204] a mixed refrigerant
cycle configured to cool a natural gas using a mixed fluorocarbon
refrigerant, wherein the mixed refrigerant cycle includes a heat
exchanger configured to allow for cooling of the natural gas via an
indirect exchange of heat between the natural gas and the mixed
fluorocarbon refrigerant; [0205] a nitrogen rejection unit (NRU)
configured to remove nitrogen from the natural gas; and [0206] a
methane autorefrigeration system configured to cool the natural gas
to produce the LNG.
[0207] 24. The hydrocarbon processing system of paragraph 23,
wherein the mixed fluorocarbon refrigerant includes a mixture of
two or more hydrofluorocarbon refrigerants.
[0208] 25. The hydrocarbon processing system of any of paragraphs 2
or 24, wherein a nitrogen stream separated from the natural gas via
the NRU is used to cool at least a portion of the natural gas.
[0209] 26. The hydrocarbon processing system of any of paragraphs
23-25, wherein the methane autorefrigeration system includes a
number of expansion devices and a number of flash drums.
[0210] 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.
* * * * *