U.S. patent application number 17/373249 was filed with the patent office on 2021-11-04 for configurations and methods for small scale lng production.
This patent application is currently assigned to Fluor Technologies Corporation. The applicant listed for this patent is Fluor Technologies Corporation. Invention is credited to John Mak.
Application Number | 20210341221 17/373249 |
Document ID | / |
Family ID | 1000005708749 |
Filed Date | 2021-11-04 |
United States Patent
Application |
20210341221 |
Kind Code |
A1 |
Mak; John |
November 4, 2021 |
CONFIGURATIONS AND METHODS FOR SMALL SCALE LNG PRODUCTION
Abstract
An LNG plant comprises a cold box and a refrigeration unit
fluidly coupled with a plurality of heat exchanger passes in the
cold box. The refrigeration unit is configured to provide a first
refrigerant stream to a first heat exchanger pass of the plurality
of heat exchanger passes at a first pressure, a second refrigerant
stream to a second heat exchanger pass at a second pressure, and a
third refrigerant stream to a third heat exchanger pass at a third
pressure. The second refrigerant stream comprises a first portion
of the first refrigerant stream, and the third refrigerant stream
comprises a second portion of the first refrigerant stream. The
second pressure and the third pressure are both below the first
pressure. The cold box is configured to produce LNG from a natural
gas feed stream to the cold box using a refrigeration content from
the refrigeration unit.
Inventors: |
Mak; John; (Santa Ana,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fluor Technologies Corporation |
Irving |
TX |
US |
|
|
Assignee: |
Fluor Technologies
Corporation
Irving
TX
|
Family ID: |
1000005708749 |
Appl. No.: |
17/373249 |
Filed: |
July 12, 2021 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15201070 |
Jul 1, 2016 |
11112173 |
|
|
17373249 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 1/0022 20130101;
F25J 1/005 20130101; F25J 2240/40 20130101; F25J 2270/16 20130101;
F25J 1/0208 20130101; F25J 1/004 20130101; F25J 2290/12 20130101;
F25J 1/0245 20130101; F25J 2220/66 20130101; F25J 1/0072 20130101;
F25J 5/00 20130101; F25J 2290/62 20130101; F25J 2210/60 20130101;
F25J 2230/60 20130101; F25J 2245/90 20130101; F25J 1/0288 20130101;
F25J 2220/68 20130101; F25J 1/0052 20130101 |
International
Class: |
F25J 1/00 20060101
F25J001/00; F25J 5/00 20060101 F25J005/00; F25J 1/02 20060101
F25J001/02 |
Claims
1. An LNG plant comprising: a cold box comprising a plurality of
heat exchanger passes; and a refrigeration unit comprising a closed
refrigeration cycle, wherein the cold box is fluidly coupled with
the refrigeration unit, wherein the cold box is configured to
receive a natural gas feed stream and produce LNG from the feed
stream using a refrigeration content from the refrigeration unit,
wherein the refrigeration unit comprises: a first compressor unit
configured to compress a refrigerant to produce a compressed
refrigerant at a first pressure; a first heat exchanger pass of the
plurality of heat exchanger passes, wherein the first heat
exchanger pass is configured to pass the compressed refrigerant
through the cold box to cool the compressed refrigerant; a splitter
configured to separate the cooled, compressed refrigerant into a
first portion and a second portion; a first expander configured to
receive the first portion from the splitter and expand the first
portion to a second pressure, wherein the second pressure is less
than the first pressure; a second expander configured to receive
the second portion from the splitter and expand the second portion
to a third pressure, wherein the third pressure is less than the
second pressure; a second heat exchanger pass of the plurality of
heat exchanger passes configured to pass the first portion at the
second pressure through the cold box; a third heat exchanger pass
of the plurality of heat exchanger passes configured to pass the
second portion at the third pressure through the cold box to
provide at least a portion of the refrigeration content in the cold
box; at least one second compressor, wherein the at least one
second compressor is configured to receive the second portion
downstream of the third heat exchanger pass and compress the second
portion to the second pressure; and a mixer, wherein the mixer is
configured to combine the compressed second portion downstream of
the at least one second compressor and the first portion downstream
of the second heat exchanger pass to form the refrigerant upstream
of the first compressor.
2. The LNG plant of claim 1, wherein the first compressor unit
comprises a plurality of compressors arranged in series and an
intercooler disposed between consecutive compressors.
3. The LNG plant of claim 1, wherein the at least one second
compressor comprises a plurality of second compressors, and wherein
at least one second compressor of the plurality of second
compressors is mechanically coupled to the first expander or the
second expander.
4. The LNG plant of claim 1, wherein the second pressure is between
about 20% and about 50% of the first pressure on an absolute
scale.
5. The LNG plant of claim 1, wherein the third pressure is between
about 3% and about 20% of the first pressure on an absolute
scale.
6. The LNG plant of claim 1, further comprising a heat exchanger
fluidly coupled between the first compressor and the first heat
exchanger pass, wherein the heat exchanger is configured to cool
the compressed refrigerant prior to the compressed refrigerant
passing to the first heat exchanger pass.
7. An LNG plant comprising: a cold box comprising a heat exchanger,
wherein the heat exchanger comprises a plurality of heat exchanger
passes; a refrigeration unit fluidly coupled with the plurality of
heat exchanger passes, wherein the refrigeration unit is configured
to provide: a first refrigerant stream to a first heat exchanger
pass of the plurality of heat exchanger passes, wherein the first
refrigerant stream is at a first pressure; a second refrigerant
stream to a second heat exchanger pass of the plurality of heat
exchanger passes, wherein the second refrigerant stream comprises a
first portion of the first refrigerant stream downstream of the
first heat exchanger pass, and wherein the second refrigerant
stream is at a second pressure; and a third refrigerant stream to a
third heat exchanger pass of the plurality of heat exchanger
passes, wherein the third refrigerant stream comprises a second
portion of the first refrigerant stream downstream of the first
heat exchanger pass, and wherein the third refrigerant stream is at
a third pressure, wherein the second pressure and the third
pressure are both below the first pressure, wherein the cold box is
configured to receive a natural gas feed stream and produce LNG
from the natural gas feed stream using a refrigeration content from
the refrigeration unit in the plurality of heat exchanger
passes.
8. The LNG plant of claim 7, wherein the first pressure is between
about 1,000 psia and 2,000 psia.
9. The LNG plant of claim 7, wherein the second pressure is between
about 20% and about 50% of the first pressure on an absolute
scale.
10. The LNG plant of claim 7, wherein the third pressure is between
about 3% and about 20% of the first pressure on an absolute
scale.
11. The LNG plant of claim 7, wherein a ratio of the second
pressure to the third pressure is between about 10:1 and about
2:1.
12. The LNG plant of claim 7, wherein a molar ratio of a flowrate
of the second refrigerant stream to a flowrate of the first
refrigerant stream is between about 0.5 and about 0.75.
13. The LNG plant of claim 7, wherein the refrigeration unit is
configured to provide the LNG at an energy of between about 320
kW/ton and about 425 kW/ton.
14. An LNG plant comprising: a cold box comprising a plurality of
heat exchanger passes; and a refrigeration unit comprising a closed
refrigeration cycle, wherein the cold box is fluidly coupled with
the refrigeration unit, wherein the cold box is configured to
receive a natural gas feed stream and produce LNG from the natural
gas feed stream using a refrigeration content from the
refrigeration unit in the plurality of heat exchanger passes,
wherein the refrigeration unit comprises: a first compressor unit
configured to compress a refrigerant to produce a compressed
refrigerant at a first pressure; a first heat exchanger pass of the
plurality of heat exchanger passes, wherein the first heat
exchanger pass is configured to pass the compressed refrigerant
through the cold box to cool the compressed refrigerant; a splitter
configured to separate the cooled, compressed refrigerant into a
first portion and a second portion; a second heat exchanger pass of
the plurality of heat exchanger passes configured to pass the first
portion at a second pressure through the cold box, wherein the
second pressure is less than the first pressure; a third heat
exchanger pass of the plurality of heat exchanger passes configured
to pass the second portion at a third pressure through the cold box
to provide at least a portion of the refrigeration content in the
cold box, wherein the third pressure is less than the second
pressure; at least one second compressor, wherein the at least one
second compressor is configured to receive the second portion
downstream of the third heat exchanger pass and compress the second
portion to the second pressure; and a mixer, wherein the mixer is
configured to combine the first portion downstream of the second
heat exchanger pass and the second portion downstream of the third
heat exchanger pass or the compressed second portion downstream of
the at least one second compressor to form the refrigerant upstream
of the first compressor.
15. The LNG plant of claim 14 further comprising a first expander
configured to receive the first portion from the splitter and
expand the first portion to the second pressure; and/or a second
expander configured to receive the second portion from the splitter
and expand the second portion to the third pressure.
16. The LNG plant of claim 14, wherein the at least one second
compressor includes a two-stage compressor.
17. The LNG plant of claim 14, wherein the mixer is downstream from
the at least one second compressor, and is configured to combine
the first portion downstream of the second heat exchanger pass and
the compressed second portion to form the refrigerant upstream of
the first compressor.
18. The LNG plant of claim 14, wherein the refrigerant consists of
one or more non-hydrocarbon refrigerants.
19. The LNG plant of claim 14, wherein the second pressure is
between 20% and 50% of the first pressure on an absolute scale, and
wherein the third pressure is between 3% and 20% of the first
pressure on an absolute scale.
20. The LNG plant of claim 14, wherein a ratio of the second
pressure to the third pressure is between about 10:1 and about 2:1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This applications claims priority to and is a divisional of
U.S. patent application Ser. No. 15/201,070 filed on Jul. 1, 2016
to Mak, entitled "Configurations and Methods for Small Scale LNG
Production," which is incorporated herein by reference it its
entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
[0003] Not applicable.
BACKGROUND
[0004] Natural gas supply in North America is continually growing,
mostly due to the production of new shale gas, recent discoveries
of offshore gas fields, and to a lesser extent, stranded natural
gas brought to market after construction of the Alaska natural gas
pipeline, and it is believed that shale gas and coal-bed methane
will make up the majority of the future growth in the energy
market.
[0005] While natural gas supply is increasing, crude oil supply is
depleting as there are no significant new discoveries of oil
reserves. If this trend continues, transportation fuel derived from
crude oil will soon become cost prohibitive, and alternate
renewable fuels (and particularly transportation fuels) are needed.
Moreover, since combustion of natural gas also produces
significantly less CO2 as compared to other fossil materials (e.g.,
coal or gasoline), use of natural gas is even more desirable.
Natural gas used for transportation fuel must be in a denser form,
either as CNG (compressed natural gas) or LNG (liquefied natural
gas). CNG is produced by compression of natural gas to very high
pressures of about 3000 to 4000 psig. However, even at such
pressures, the density of CNG is relatively low, and storage at
high pressure requires heavy weight vessels and is potentially a
hazard. On the other hand, LNG has a significantly higher density
and can be stored at relatively low pressures of about 20 to 150
psig. Still further, LNG is a safer fuel than CNG, as it is at
lower pressure and not combustible until it is vaporized and mixed
with air in the proper ratio. Nevertheless, CNG is more common than
LNG as a transportation fuel, mainly due to the cost of high
liquefaction and the lack of infrastructure to support LNG fueling
facilities.
[0006] LNG can be used to replace diesel and is presently used in
many heavy duty vehicles, including refuse haulers, grocery
delivery trucks, transit buses, and coal miner lifters. To increase
the LNG fuel markets, small to mid-scale LNG plants must be
constructed close to both pipelines and LNG consumers, as long
distance transfer of LNG is costly and therefore often not
economical. Such small to mid-scale LNG plants should be designed
to produce 0.2 mtpy to 2.0 mtpy (million tonnes per year).
Moreover, such small to mid-scale LNG plants must be simple in
design, easy to operate, and sufficiently robust to support an
unmanned operation. Still further, it would be desirable to
integrate liquefaction with LNG truck fueling operations to allow
for even greater delivery flexibility.
[0007] Various refrigeration processes are used for LNG
liquefaction. The most common of these refrigeration processes are
the cascade process, the mixed refrigerant process, and the propane
pre-cooled mixed refrigerant process. While these methods are
energy efficient, such methods are often complex and require
circulating several hydrocarbon refrigerants or mixed hydrocarbon
refrigerants. Unfortunately, such refrigerants (e.g., propane,
ethylene, and propylene) are explosive and hazardous in the event
of leakage.
[0008] There are several recent innovations in LNG plant design.
For example, U.S. Pat. No. 5,755,114 to Foglietta teaches a hybrid
liquefaction cycle which includes a closed loop propane
refrigeration cycle and a turboexpander cycle. Compared to other
liquefaction processes, the liquefaction process has been
simplified, but is still unsuitable and/or economically
unattractive for small to mid-scale LNG plants. U.S. Pat. No.
7,673,476 to Whitesell discloses a compact and modular liquefaction
system that requires no external refrigeration. The system uses gas
expansion by recycling feed gas to generate cooling. While this
design is relatively compact, operation of the recycle system is
complicated, and the use of hydrocarbon gas for cooling remains a
safety concern. U.S. Pat. No. 5,363,655 to Kikkawa teaches the use
of gas expander and plate and fin heat exchangers for LNG
liquefaction. While providing several advantages, such process is
still too complex and costly for small to mid-scale LNG plants.
[0009] Further compounding the above noted drawbacks is the fact
that most of the systems lack the capability for integration of a
small to mid-scale LNG plant with an LNG loading operation. Thus,
the current practice for loading an LNG truck generally requires an
LNG pump to pump the LNG from the storage tanks to the LNG trucks.
Remarkably, the boil-off vapors generated during the LNG truck
loading operation are vented to the atmosphere which is a safety
hazard and creates emission pollution.
[0010] Thus, various disadvantages remain. Among other things, most
of the LNG liquefaction methods and configurations are complex and
costly and hence unsuitable for the small to mid-scale LNG plants.
In addition, most liquefaction plants lack an integrated system for
LNG loading operations, which is highly desirable for small to
mid-scale LNG plants.
SUMMARY
[0011] In an embodiment, an LNG plant comprises a cold box
comprising a plurality of heat exchanger passes and a refrigeration
unit comprising a closed refrigeration cycle. The cold box is
fluidly coupled with the refrigeration unit, and the cold box is
configured to receive a natural gas feed stream and produce LNG
from the feed stream using a refrigeration content from the
refrigeration unit. The refrigeration unit comprises a first
compressor unit configured to compress a refrigerant to produce a
compressed refrigerant at a first pressure, a first heat exchanger
pass of the plurality of heat exchanger passes that is configured
to pass the compressed refrigerant through the cold box to cool the
compressed refrigerant, a splitter configured to separate the
cooled, compressed refrigerant into a first portion and a second
portion, a first expander configured to receive the first portion
from the splitter and expand the first portion to a second
pressure, a second expander configured to receive the second
portion from the splitter and expand the second portion to a third
pressure, a second heat exchanger pass of the plurality of heat
exchanger passes configured to pass the first portion at the second
pressure through the cold box, a third heat exchanger pass of the
plurality of heat exchanger passes configured to pass the second
portion at the third pressure through the cold box to provide at
least a portion of the refrigeration content in the cold box, at
least one second compressor that is configured to receive the
second portion downstream of the third heat exchanger pass and
compress the second portion to the second pressure, and a mixer
that is configured to combine the compressed second portion
downstream of the at least one second compressor and the first
portion downstream of the second heat exchanger pass to form the
refrigerant upstream of the first compressor. The second pressure
is less than the first pressure, and the third pressure is less
than the second pressure.
[0012] In an embodiment, an LNG plant comprises a cold box
comprising a heat exchanger that has a plurality of heat exchanger
passes and a refrigeration unit fluidly coupled with the plurality
of heat exchanger passes. The refrigeration unit is configured to
provide a first refrigerant stream to a first heat exchanger pass
of the plurality of heat exchanger passes at a first pressure, a
second refrigerant stream to a second heat exchanger pass of the
plurality of heat exchanger passes, and a third refrigerant stream
to a third heat exchanger pass of the plurality of heat exchanger
passes. The second refrigerant stream comprises a first portion of
the first refrigerant stream downstream of the first heat exchanger
pass, and the second refrigerant stream is at a second pressure.
The third refrigerant stream comprises a second portion of the
first refrigerant stream downstream of the first heat exchanger
pass, and the third refrigerant stream is at a third pressure. The
second pressure and the third pressure are both below the first
pressure. The cold box is configured to receive a natural gas feed
stream and produce LNG from the natural gas feed stream using a
refrigeration content from the refrigeration unit in the plurality
of heat exchanger passes.
[0013] In an embodiment, a method of generating LNG from a natural
gas feed comprises passing a first refrigerant stream through a
first heat exchanger pass of a plurality of heat exchanger passes
in a cold box at a first pressure, separating the first refrigerant
stream into a second refrigerant stream and a third refrigerant
stream downstream of the cold box, passing the second refrigerant
stream through a second heat exchanger pass of the plurality of
heat exchanger passes at a second pressure, passing the third
refrigerant stream through a third heat exchanger pass of the
plurality of heat exchanger passes, passing a natural gas feed
stream through at least a fourth heat exchanger pass of the
plurality of heat exchanger passes, and liquefying at least a
portion of the natural gas stream in the cold box using a
refrigeration content provided by at least one of the second
refrigerant stream or the third refrigerant stream to form an LNG
stream. The third refrigerant stream is at a third pressure, and
the second pressure and the third pressure are both below the first
pressure.
[0014] Various objects, features, aspects and advantages will
become more apparent from the following detailed description of
various embodiments along with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is one exemplary configuration according to an
embodiment using a nitrogen cycle.
[0016] FIG. 2 is another exemplary configuration according to an
embodiment using a nitrogen cycle with an integrated LNG
loading.
[0017] FIG. 3 is an exemplary graph illustrating the close
temperature approach of the heat composite curves between the feed
gas and the refrigeration circuit of FIG. 2.
DETAILED DESCRIPTION
[0018] It should be understood at the outset that although
illustrative implementations of one or more embodiments are
illustrated below, the disclosed systems and methods may be
implemented using any number of techniques, whether currently known
or not yet in existence. The disclosure should in no way be limited
to the illustrative implementations, drawings, and techniques
illustrated below, but may be modified within the scope of the
appended claims along with their full scope of equivalents.
[0019] The following brief definition of terms shall apply
throughout the application:
[0020] The term "comprising" means including but not limited to,
and should be interpreted in the manner it is typically used in the
patent context;
[0021] The phrases "in one embodiment," "according to one
embodiment," and the like generally mean that the particular
feature, structure, or characteristic following the phrase may be
included in at least one embodiment of the present invention, and
may be included in more than one embodiment of the present
invention (importantly, such phrases do not necessarily refer to
the same embodiment);
[0022] If the specification describes something as "exemplary" or
an "example," it should be understood that refers to a
non-exclusive example;
[0023] The terms "about," "approximately" or the like, when used
with a number, may mean that specific number, or alternatively, a
range in proximity to the specific number, as understood by persons
of skill in the art field; and
[0024] If the specification states a component or feature "may,"
"can," "could," "should," "would," "preferably," "possibly,"
"typically," "optionally," "for example," "often," or "might" (or
other such language) be included or have a characteristic, that
particular component or feature is not required to be included or
to have the characteristic. Such component or feature may be
optionally included in some embodiments, or it may be excluded.
[0025] The systems and methods described herein are directed to
natural gas liquefaction and LNG (liquefied natural gas) truck
loading, and especially use of gas expansion processes for small to
mid-scale LNG plants and integration of natural gas liquefaction
with an LNG truck loading facility. As described herein, a small to
mid-scale LNG plant can be integrated with an LNG truck loading
facility in a simple and cost-effective manner. In some aspects,
the small to mid-scale LNG plant can have a capacity of typically
about 0.2 mtpy to about 0.7 mtpy, typically between about 0.7 mtpy
to about 1.5 mtpy, and most typically between about 1.5 mtpy to
about 2.5 mtpy of LNG by liquefaction of appropriate quantities of
feed gas. For some applications, the contemplated process may also
be suitable for producing LNG below about 0.1 mtpy. In further
aspects, the refrigeration process uses a non-hydrocarbon
refrigerant (e.g., nitrogen, air, etc.) in a compression expansion
cycle to so avoid the safety issues commonly associated with a
hydrocarbon refrigeration system.
[0026] As disclosed herein, natural gas (e.g., delivered from a
pipeline) can be liquefied in a cold box using a gas expansion
cycle that employs a two-stage compressor to so produce at least
two pressure level gases. The so produced gases are then cooled and
expanded to a lower pressure to thereby generate refrigeration
prior to mixing in a heat exchanger as a single gas stream that is
then fed to the compressors that are driven by the expanders.
[0027] The expander cycle can use nitrogen that is inherently safe
to operate and more reliable than conventional mixed refrigerant
processes while the nitrogen expander cycle can be of low pressure
or high pressure design to match the feed gas composition and
pressure with power consumption per unit of LNG produced of about
320 to about 425 kW/ton.
[0028] In some embodiments, the LNG loading facility has a pressure
control system that uses high pressure feed gas as a motive force
to move the LNG product from an LNG storage tank to an LNG truck
while boil-off vapors from the LNG truck are recovered in the
liquefaction plant.
[0029] In one aspect, a small to mid-scale LNG plant can have an
integrated loading terminal, wherein the plant includes a cold box
with a closed refrigeration cycle (preferably a two stage expander
refrigeration system, operating with a non-hydrocarbon refrigerant)
to so provide refrigeration content to a natural gas feed at a
temperature sufficient to produce LNG from the natural gas feed. It
is generally preferred that an LNG storage tank is thermally
coupled to the refrigeration cycle to receive and store the LNG,
and that a first boil off vapor line provides a first boil off
vapor from an LNG transporter to the cold box, and from the cold
box to the LNG storage tank, while a second boil off vapor line
provides a second boil off vapor from the LNG storage tank to the
cold box, and from the cold box to the natural gas feed. Most
typically, a compressor compresses at least one of the first and
second boil off vapors, and/or a differential pressure controller
maintains a predetermined pressure differential (e.g., 5-200 psi,
more typically 10-50 psi) between the LNG storage tank and the LNG
transporter.
[0030] In another aspect, LNG from the storage tank is unloaded
from the top of the storage tank using an internal pipe in the
storage tank, which eliminates the potential hazards of LNG
spillage of the LNG tank inventory typically used in commonly used
tank configurations.
[0031] Therefore, and viewed from a different perspective, a method
of liquefying natural gas and loading the LNG to an LNG transporter
will include a step of liquefying natural gas feed in a cold box
using a closed refrigeration cycle, and feeding the LNG to an LNG
storage tank. In another step, a first boil off vapor from an LNG
transporter is cooled and compressed and used as a motive force to
deliver LNG from the LNG storage tank to the LNG transporter. In
such methods, a second boil off vapor from the LNG storage tank can
be cooled and compressed and moved from the cold box to the natural
gas feed. As before, the step of liquefying a natural gas feed can
be performed using a two stage closed refrigeration cycle,
typically using a non-hydrocarbon refrigerant, such as
nitrogen.
[0032] FIG. 1 illustrates an embodiment of a LNG liquefaction
system 100. Feed gas stream 102 can be supplied to the small scale
LNG liquefaction plant. The feed gas stream can comprise primarily
light hydrocarbons, such as methane and ethane. Minor amounts of
various other gases, including inert gases such as nitrogen, argon
and the like, can also be present. The feed gas stream can be
treated in a gas treatment unit that typically includes an amine
unit and a dehydration unit for removal of CO2 and water, forming a
dry and substantially CO2 free gas stream. The feed gas stream may
have a temperature of between about 50.degree. F. and 200.degree.
F. and a pressure of between about 100 psia and 700 psia. The feed
gas stream 102 can enter the cold box 151, which can comprise a
plurality of heat exchanger passes 152, 153, 154, and 155. While
four heat exchanger passes are shown in FIG. 1, more than four heat
exchanger passes or less than four heat exchanger passes can also
be used with the system 100. The feed gas can be chilled by
nitrogen refrigeration in heat exchanger pass 152 and form a
sub-cooled LNG stream 103, which can then be let down in pressure
in a downstream JT valve forming a flashed LNG stream. The flashed
vapor can be returned to the liquefaction unit and the resulting
liquid LNG can be stored in a LNG storage tank, as described in
more detail herein.
[0033] The refrigeration for the cold box 151 can be provided by
the closed refrigeration cycle. As shown in FIG. 1, the closed
refrigeration cycle can comprise a two-stage liquefaction cycle
using a high-pressure refrigerant cycle, typically operating at
pressures greater than about 1,000 psia. In the refrigeration
cycle, stream 126 from compressor 150 can be discharged at a
pressure between about 400 psia and 600 psia to feed the compressor
unit 160, which compresses the refrigerant gas to greater than
about 1,000 psia (e.g., greater than 1,100 psia, greater than 1,200
psia, or greater than 1,300 psia) to form stream 128. The
compressor unit 160 may generally have an upper compression limit
of around 1,500 psia, though the stream 126 may not be compressed
to this limit in most configurations. The compressor unit 160 can
comprise single-stage or multi-stage compressors, optionally with
intercoolers. The compressor discharge can be cooled in cooler 164
to form stream 129, which can be further cooled in the cold box 151
in exchanger pass 155 to between -10.degree. F. and about
-50.degree. F. forming stream 130. Stream 130 can be split into two
portions: streams 130a and 130b. The molar ratio of the two streams
can be divided into any suitable amounts, which can be based on the
feed gas composition and/or the pressure. In some aspects, the two
streams 130a and 130b can be split at a molar ratio of stream 130a
to stream 130 of between about 0.5 and about 0.75, or between about
0.6 and about 0.7, or at about 0.68.
[0034] Stream 130a can be expanded in expander 170 to between about
20% and about 50%, or between about 30% and about 45%, or between
about 35% and about 42% of the original pressure on an absolute
pressure scale to form stream 179 that passes through heat
exchanger pass 153. Stream 179 can cool the feed gas stream 102 and
the high-pressure refrigerant stream 129 in the cold box 151.
Stream 179 can pass out of the cold box 151 as stream 132. Stream
130b can be expanded in expander 180 to between about 3% and about
20%, or between about 4% and about 15%, or between about 5% and
about 10%, or between about 7% and about 9% of the original
pressure on an absolute pressure scale to form stream 127 that
passes through heat exchanger pass 154. Stream 127 can be used to
cool the feed gas and the high-pressure refrigerant in the cold box
151. Stream 127 can pass out of the cold box 151 as stream 121,
which can then be compressed by compressor 150 to a pressure
substantially the same as the pressure of stream 179, and stream
121 can then be mixed with stream 132 to form stream 120 as feed to
the compressor 160.
[0035] The use of two expanded refrigerant flow paths through the
cold box 151 may allow for a more efficient cooling in some
instances. In an embodiment, the two lower pressure streams passing
through separate heat exchanger passes through the cold box 151 can
have a relative pressure ratio of between about 10:1 and about 2:1,
between about 7:1 and about 3:1, or between about 5:1 and about
4:1, each as a ratio of the higher pressure refrigerant stream 179
to lower pressure refrigerant stream 127 on an absolute pressure
scale.
[0036] Thus, the closed refrigeration cycle can comprise a cold box
having multiple heat exchanger passes, including a plurality of
heat exchanger passes for the refrigerant and at least one heat
exchanger pass for the natural gas feed stream. The refrigeration
unit is fluid coupled to the cold box and the plurality of heat
exchanger passes to provide the refrigerant and refrigeration
content for forming LNG from the natural gas feed stream in the
cold box. As shown in FIG. 1, the refrigeration unit is configured
to provide at least a first refrigerant stream to a first heat
exchanger pass of the plurality of heat exchanger passes. The first
refrigerant stream can be at a first pressure, which can be a
relatively high pressure after being compressed in compressor unit
160. The refrigeration unit is also configured to provide a second
refrigerant stream to a second heat exchanger pass in the cold box.
The second refrigerant stream can be a portion of the compressed
refrigerant stream resulting from splitting the compressed
refrigerant stream downstream of the first heat exchanger pass. The
second refrigerant stream can be expanded (e.g., using an expander)
such that the second refrigerant stream can be at a second pressure
that is lower than the compressed pressure at the entrance to the
second heat exchanger pass. The refrigeration unit can also provide
a third refrigerant stream to a third heat exchanger pass. The
third refrigerant stream can be the remaining portion of the
compressed refrigerant stream resulting from splitting the
compressed refrigerant stream downstream of the first heat
exchanger pass. The third refrigerant stream can be expanded (e.g.,
using an expander) such that the third refrigerant stream is at a
third pressure that is lower than the second pressure at the
entrance to the third heat exchanger pass. The second and/or third
heat exchanger passes can provide the refrigeration content within
the cold box. The resulting refrigeration content can then be used
to form the LNG from the natural gas in the natural gas feed stream
with power consumption per unit of LNG produced of about 320 kW/ton
to about 425 kW/ton.
[0037] FIG. 2 illustrates another embodiment of an LNG production
system 200. The refrigeration unit of FIG. 2 is similar to the
refrigeration unit of the system 100 illustrated in FIG. 1, and the
differences will be described in more detail with reference to FIG.
2. In the system 200, the feed gas stream 201 can be supplied to
the LNG liquefaction plant at any suitable flow rate, temperature,
and pressure. The feed gas stream can be the same or similar to the
feed gas stream 102 described with respect to FIG. 1, including the
composition, pressure, and temperature. In an embodiment and as an
example of suitable conditions, the feed gas stream 201 can be
delivered at a flow rate of about 1.7 MMscfd, at a temperature of
about 100.degree. F., and at a pressure of about 453 psia. As a
further example, the feed gas stream can have a composition
comprising about 1.0 mol % N.sub.2, about 0.1 mol % CO.sub.2, about
96.5 mol % methane, about 2 mol % ethane, and about 0.5 mol %
propane and heavier components. The feed gas can be treated in a
gas treatment unit 241 that can include an amine unit and/or a
dehydration unit (e.g., a molecular sieve dehydration unit) for the
removal of CO.sub.2 and water, forming a substantially dry and
CO.sub.2 free gas stream 202.
[0038] The dried gas stream 202 can be combined with a recycle gas
stream 211, as described in more detail herein, and can enter the
cold box 251, which typically comprises a plurality of heat
exchanger passes, 152, 153, 154, 155, and 156. The feed gas 102 can
be chilled by nitrogen refrigeration in heat exchanger pass 152 to
form a sub-cooled stream 203 and can then be let down in pressure
in Joule-Thomson valve 271 to form stream 204. As an example, the
sub-cooled stream can be cooled to about -223.degree. F., and the
flashed liquid downstream of the JT valve 271 can be at about
-227.degree. F. The flashed liquid can be stored in storage tank
265, which can operate at a pressure above atmospheric, e.g.,
between about 20 psia and 100 psi, or at about 60 psia. The flashed
gas stream 208 can be recovered by recycling the gas in stream 208
back to the exchanger pass 156 via valve 270. As the gas in stream
208 is in equilibrium with the liquid in the storage tank 265, the
gas can have a temperature less than that of the other streams in
the cold box 151. The refrigeration content of this recycle stream
can be recovered in the cold box 151. Thus, it should be noted that
the flashed stream from the storage tank 265 can be heated in the
cold box 151. Once the gas stream passes through the cold box 151
to form stream 210, the stream 210 can exit the cold box 151 and be
compressed by compressor 268 to a pressure at or above the feed gas
pressure to form stream 211 prior to mixing with feed gas stream
102.
[0039] The two-stage nitrogen liquefaction cycle can also be
configured using a high-pressure nitrogen cycle, typically
operating at above 1,000 psia (e.g., at or above about 1,100 psia,
1,200 psia, 1,300 psia, etc.) as described above with respect to
FIG. 1. Nitrogen or air can be used in this cycle as long as the
gas is dry. The hydrocarbon content is monitored as known in the
art to detect any leakages, and the unit can immediately shut down
during emergency. The refrigeration cycle shown in FIG. 2 is
similar to the refrigeration cycle shown in FIG. 1 except that the
compressor unit 160 shown in FIG. 1 can comprise a two-stage
compressor as shown in FIG. 2. Further, the compressor unit 150
that compresses a portion of the refrigerant stream can comprise a
two-stage compression, where the two-stage compression can be
mechanically coupled to the parallel expanders 170, 180 as shown in
FIG. 1.
[0040] The gas pretreatment, vapor handling and the loading system
are the same as in the previous design; the difference being the
design of the liquefaction cycle. As shown in FIG. 1, feed gas is
chilled and at least partially liquefied by the refrigeration cycle
in the exchanger pass 152 to form a sub-cooled stream 103. As an
example, the sub-cooled stream can be at about -238.degree. F.,
which can then be let down in pressure in the JT valve 271 to form
stream 204 that passes to the storage tank 265 as described
above.
[0041] Within the refrigeration cycle, stream 226 from compressor
260, which can optionally be mechanically coupled to the expander
259, can be discharged, and optionally cooled in ambient cooler
212, prior to being combined with stream 132 to form the feed to
the compressor unit. As an example, the stream 226 can be
compressed to about 507 psia prior to being combined with stream
132. The compressor unit can comprise a two-stage refrigerant
compressor unit comprising compressor 261 and compressor 262 with
an intercooler 263. For example stream 120 can be compressed in
compressor 261, the compressed stream 22 can pass to the
intercooler 263, and the cooled, compressed stream 223 can then
pass to the second-stage compressor 262. The compressor unit can
compress the refrigerant to a high pressure above 1,000 psi, or
another of the other pressures disclosed herein. The compressed
refrigerant stream 128 can be cooled in an ambient cooler 164 to
form stream 129. The ambient cooler 164 can comprise any suitable
heat exchanger to cool the compressed refrigerant such as an air
exchanger, water exchanger, or the like.
[0042] Stream 129 can pass from the ambient cooler 164 to the cold
box 151 and pass through heat exchanger pass 155 to cool the high
pressure refrigerant stream and form stream 130. As an example, the
refrigerant in stream 129 can be cooled to form stream 130 at about
-30.degree. F. Stream 130 can then be split into two portions
including stream 130a and 130b. The molar ratio of the two streams
can be divided into any suitable amounts (e.g., as disclosed with
respect to FIG. 1), which can be based on the feed gas composition
and/or the pressure. In some aspects, the two streams 130a and 130b
can be split at any of the molar ratios described with respect to
FIG. 1.
[0043] Stream 130a can be expanded in expander 257 to form stream
179. The expander 257 can be the same or similar to the expander
170 described with respect to FIG. 1. The expander can expand
stream 130a according to any of the pressure ranges described with
respect to FIG. 1. As an example, stream 130a can be expanded from
about 1282 psia to about 508 psia, which is a ratio of about 40%.
The expansion of stream 130a in the expander 257 can result in the
formation of stream 179, which can be passed back to the cold box
151 in heat exchanger pass 153. As an example, the expansion of
stream 130a can result in stream 179 having a temperature of about
-126.degree. F. Stream 179 can be used to cool the feed gas stream
102 and the high-pressure nitrogen steam 129 in heat exchanger pass
153 to form stream 132. As an example, stream 132 can leave the
cold box 151 at about 507 psia and about 94.degree. F.
[0044] Stream 130b can be expanded in expander 259 to form stream
127. The expander 159 can be the same or similar to the expander
180 described with respect to FIG. 1. The expander 159 can expand
stream 130b according to any of the pressure ranges described with
respect to FIG. 1. Further, the relative pressure ratios of the two
expanded streams to each other and relative to the high pressure
stream can fall within any of the ranges described with respect to
FIG. 1. As an example, stream 130b can be expanded from about 1282
psia to about 110 psia using expander 259, which results in stream
127 have a pressure that is about 8.5% of the pressure of stream
130b. The expansion can result in stream 127 having a lower
temperature, for example, about -242.degree. F. Stream 127 can then
be used to cool the feed gas 102 and the high pressure refrigerant
stream in heat exchanger pass 154. The low pressure stream 121 can
then be compressed prior to being combined with stream 132. As
shown in FIG. 2, the stream 121 can be compressed by compressor
258, pass through line 233, and be compressed by a second-stage
compressor 260 to compress the portion of the refrigerant to a
pressure at or above the pressure in stream 132. As compared to
FIG. 1, the compression of the stream 121 can be carried out in a
two-stage compression using compressors 258, 260 arranged in
series. As an example of the compression conditions, stream 121 can
be compressed in compressors 258, 260 to about 508 psia, so that
the stream 121 can be combined with stream 132 to form stream 120
as the feed to the refrigerant compressors 261, 262.
[0045] As shown in FIG. 2, the expansion and compression cycles can
be mechanically coupled. For example, the expanders used to expand
streams 130a and 130b can be mechanically coupled to the
compressors for the low-pressure stream 121 leaving heat exchanger
pass 154. Specifically, the expander 257 can be mechanically
coupled to compressor 258, and the expander 259 can be mechanically
coupled to compressor 260. This type of configuration can be used
to reduce the overall compression energy requirements. FIG. 3
illustrates a heat composite curve showing the temperature
approaches between the feed gas and the refrigeration circuit
according to the system described with respect to FIG. 2. This
composite heat curve demonstrates the efficiency in achieving the
natural gas liquefaction of the system described herein.
[0046] During conventional LNG truck loading operations, LNG is
typically pumped using LNG pumps from the storage tank to the LNG
trucks. This operation requires at least 2 hours' time, as the LNG
truck must be chilled from typically ambient temperature to
cryogenic temperature. This operation also generates a significant
amount of boil-off vapors, which are in most cases vented to
atmosphere and so present a substantial environmental concern.
[0047] In contrast, and as is shown in FIG. 2, LNG can be
transferred from the LNG storage tank 265 to LNG transport 267 via
streams 205, 206 and loading hose 266 by pressure differential,
thereby allowing filling operation without the use of an LNG pump.
LNG can be transferred from a top outlet nozzle 298 using an
internal pipe 299 inside the storage tank 265. This configuration
helps avoid any bottom nozzles from the storage tank 265, thereby
avoiding spillage of the storage tank inventory typically
encountered in conventional storage tank design. Consequently, LNG
pumps are not required. Flow controller 282 can be adjusted as
necessary to deliver the flow quantity to the LNG transport 267.
When the level in the storage tank 265 drops to a low level, the
level control 297 can reduce or stop flow in stream 205 at a
predetermined low level. The LNG storage tank 265 can be configured
with a capacity of between about 10,000 gallons and about 50,000
gallons, or about 30,000 gallons, which is sufficient to load at
least two LNG transports 267, such as LNG trucks, each with 10,000
gallons capacity. During LNG truck loading operation, the valve 270
is closed, and the valve 269 is open, allowing boil-off vapor
stream 207 to be vented from the LNG transport 267 to the cold box
151 as stream 209. Valve 269 can control the LNG transport vapor
header at about 50 psig using the pressure controller 281, the
lower pressure set-point of the LNG transport 267. With these
valves operating in tandem, the boil-off vapors during loading are
recovered, and venting to atmosphere is avoided. In some
embodiments, the boil-off vapors can be at a lower temperature than
the streams in the cold box 151, and routing these boil-off vapors
back to the cold box 151 can allow the refrigerant content of the
boil-off vapors to be recovered in the cold box 151.
[0048] In order to provide the driving force to pressurize the LNG
inventory within the storage tank 265 and pass the LNG from the
storage tank 265 to the LNG transport 267, valve 284 can be opened
to provide high pressure gas in stream 285 to the storage tank 265.
A pressure differential controller 288 and a pressure controller
283 can be used to control the flow rate of the LNG to the LNG
transport 267. Typically, the pressure differential can be set at
about 10 psi or higher, depending on the distance between the
storage tank 265 and the LNG transport 267. The LNG loading rate
can be varied from about 250 GPM to about 500 GPM using the flow
controller 282. In general, the differential pressure can be
increased to increase the loading rate. Therefore, it should be
appreciated that LNG pumping is not necessary, and the loading
system size and cost can be significantly reduced.
[0049] While contemplated methods and plants presented herein may
have any capacity, it should be appreciated that such plants and
methods are especially suitable for a small to mid-scale LNG plant
having capacity of typically between 0.2 to 0.7 mtpy (million
tonnes per year), more typically between 0.7 to 1.5 mtpy, and most
typically between 1.5 to 2.5 mtpy of LNG production by liquefaction
of appropriate quantities of feed gas. Consequently, contemplated
plants and methods may be implemented at any location where
substantial quantities of natural gas are available, and especially
preferred locations include gas producing wells, gasification
plants (e.g., coal and other carbonaceous materials), and at
decentralized locations using gas from a natural gas pipeline.
Thus, it should be recognized that the feed gas composition may
vary considerably, and that depending on the type of gas
composition, one or more pre-treatment units may be required. For
example, suitable pre-treatment units include dehydration units,
acid gas removal units, etc.
[0050] It is further noted that use of a cold box with an inert gas
is particularly preferred, especially where the
liquefaction/filling station is in an urban environment. However,
various other cryogenic devices are also deemed suitable, and
alternative devices include those that use mixed hydrocarbon
refrigerants. Moreover, and particularly where the storage tank has
a somewhat larger capacity, it is contemplated that refrigeration
content from the LNG may also be used to supplement refrigeration
requirements.
[0051] With respect to the differential pressure controller (dPC),
it is noted that the dPC is preferably implemented as a control
device with a CPU, and may therefore be configured as a
suitably-programmed personal computer or programmable logic
controller. It is also generally preferred that the dPC is
configured such that the dPC controls operation of control valves
to thereby maintain a predetermined pressure differential between
the storage tank and the tank in the LNG transport vessel using
pressure sensors and valves as is well known in the art. For
example, control may be achieved by regulating pressure and/or flow
volume of compressed boil-off vapor from the compressor outlet en
route to the storage tank, by regulating pressure and/or flow
volume of boil-off vapor from the tank in the LNG transport vessel,
and/or by regulating pressure and/or flow volume of LNG from the
storage tank to the tank in the LNG transport vessel. Thus, in at
least some embodiments, the differential pressure controller will
be configured to allow liquefaction operation concurrent with
filling operation of the LNG transporter. Therefore, feeding of the
natural gas to the liquefaction unit is done in a continuous
manner. However, discontinuous feeding and liquefaction is also
contemplated.
[0052] It should be noted that contrary to most known
configurations, at least a portion of the boil-off vapor from the
storage tank and/or tank in the LNG transport vessel is not
liquefied, but used as a motive fluid to move LNG from the storage
tank to the tank in the LNG transport vessel. Consequently, the
need for a LNG pump is eliminated. Moreover, it should be noted
that the refrigeration content of the boil-off vapor from the tank
in the LNG transport vessel can be employed to supplement
refrigeration requirements in the cold box. Thus, the boil-off
vapor is heated rather than cooled and reliquefied as known in most
operations.
[0053] It is still further contemplated that the storage tank may
be modified in a manner such that LNG for export from the storage
tank is drawn from a lower portion of the storage tank (e.g., sump
or other location, typically below the center of gravity of the
tank) through the vapor space of the tank to the filling
line/loading hose, thereby avoiding problems associated with
filling ports at the lower portion of the storage tank. Most
typically, the tank will include an internal fill pipe that
terminates at an upper portion of the tank to so allow connecting
the internal fill pipe to a filling line/loading hose.
[0054] Having described the systems and methods herein, various
aspects can include, but are not limited to:
[0055] In a first aspect, an LNG plant comprises a cold box
comprising a plurality of heat exchanger passes; and a
refrigeration unit comprising a closed refrigeration cycle, wherein
the cold box is fluidly coupled with the refrigeration unit,
wherein the cold box is configured to receive a natural gas feed
stream and produce LNG from the feed stream using a refrigeration
content from the refrigeration unit, wherein the refrigeration unit
comprises: a first compressor unit configured to compress a
refrigerant to produce a compressed refrigerant at a first
pressure; a first heat exchanger pass of the plurality of heat
exchanger passes, wherein the first heat exchanger pass is
configured to pass the compressed refrigerant through the cold box
to cool the compressed refrigerant; a splitter configured to
separate the cooled, compressed refrigerant into a first portion
and a second portion; a first expander configured to receive the
first portion from the splitter and expand the first portion to a
second pressure, wherein the second pressure is less than the first
pressure; a second expander configured to receive the second
portion from the splitter and expand the second portion to a third
pressure, wherein the third pressure is less than the second
pressure; a second heat exchanger pass of the plurality of heat
exchanger passes configured to pass the first portion at the second
pressure through the cold box; a third heat exchanger pass of the
plurality of heat exchanger passes configured to pass the second
portion at the third pressure through the cold box to provide at
least a portion of the refrigeration content in the cold box; at
least one second compressor, wherein the at least one second
compressor is configured to receive the second portion downstream
of the third heat exchanger pass and compress the second portion to
the second pressure; and a mixer, wherein the mixer is configured
to combine the compressed second portion downstream of the at least
one second compressor and the first portion downstream of the
second heat exchanger pass to form the refrigerant upstream of the
first compressor.
[0056] A second aspect can include the LNG plant of the first
aspect, wherein the first compressor unit comprises a plurality of
compressors arranged in series and an intercooler disposed between
consecutive compressors.
[0057] A third aspect can include the LNG plant of the first or
second aspects, wherein the at least one second compressor
comprises a plurality of second compressors, and wherein at least
one second compressor of the plurality of second compressors is
mechanically coupled to the first expander or the second
expander.
[0058] A fourth aspect can include the LNG plant of any of the
first to third aspects, wherein the second pressure is between
about 20% and about 50% of the first pressure on an absolute
scale.
[0059] A fifth aspect can include the LNG plant of any of the first
to fourth aspects, wherein the third pressure is between about 3%
and about 20% of the first pressure on an absolute scale.
[0060] A sixth aspect can include the LNG plant of any of the first
to fifth aspects, further comprising a heat exchanger fluidly
coupled between the first compressor and the first heat exchanger
pass, wherein the heat exchanger is configured to cool the
compressed refrigerant prior to the compressed refrigerant passing
to the first heat exchanger pass.
[0061] In a seventh aspect, an LNG plant comprises a cold box
comprising a heat exchanger, wherein the heat exchanger comprises a
plurality of heat exchanger passes; a refrigeration unit fluidly
coupled with the plurality of heat exchanger passes, wherein the
refrigeration unit is configured to provide: a first refrigerant
stream to a first heat exchanger pass of the plurality of heat
exchanger passes, wherein the first refrigerant stream is at a
first pressure; a second refrigerant stream to a second heat
exchanger pass of the plurality of heat exchanger passes, wherein
the second refrigerant stream comprises a first portion of the
first refrigerant stream downstream of the first heat exchanger
pass, and wherein the second refrigerant stream is at a second
pressure; and a third refrigerant stream to a third heat exchanger
pass of the plurality of heat exchanger passes, wherein the third
refrigerant stream comprises a second portion of the first
refrigerant stream downstream of the first heat exchanger pass, and
wherein the third refrigerant stream is at a third pressure,
wherein the second pressure and the third pressure are both below
the first pressure; wherein the cold box is configured to receive a
natural gas feed stream and produce LNG from the natural gas feed
stream using a refrigeration content from the refrigeration unit in
the plurality of heat exchanger passes.
[0062] An eighth aspect can include the LNG plant of the seventh
aspect, wherein the first pressure is between about 1,000 psia and
2,000 psia.
[0063] A ninth aspect can include the LNG plant of the seventh or
eighth aspect, wherein the second pressure is between about 20% and
about 50% of the first pressure on an absolute scale.
[0064] A tenth aspect can include the LNG plant of any of the
seventh to ninth aspects, wherein the third pressure is between
about 3% and about 20% of the first pressure on an absolute
scale.
[0065] An eleventh aspect can include the LNG plant of any of the
seventh to tenth aspects, wherein a ratio of the second pressure to
the third pressure is between about 10:1 and about 2:1.
[0066] A twelfth aspect can include the LNG plant of any of the
seventh to eleventh aspects, wherein a molar ratio of a flowrate of
the second refrigerant stream to a flowrate of the first
refrigerant stream is between about 0.5 and about 0.75.
[0067] A thirteenth aspect can include the LNG plant of any of the
seventh to twelfth aspects, wherein the refrigeration unit is
configured to provide the LNG at an energy of between about 320
kW/ton and about 425 kW/ton.
[0068] In a fourteenth aspect, a method of generating LNG from a
natural gas feed comprises passing a first refrigerant stream
through a first heat exchanger pass of a plurality of heat
exchanger passes in a cold box, wherein the first refrigerant
stream is at a first pressure; separating the first refrigerant
stream into a second refrigerant stream and a third refrigerant
stream downstream of the cold box; passing the second refrigerant
stream through a second heat exchanger pass of the plurality of
heat exchanger passes, wherein the second refrigerant stream is at
a second pressure; passing the third refrigerant stream through a
third heat exchanger pass of the plurality of heat exchanger
passes, wherein the third refrigerant stream is at a third
pressure, wherein the second pressure and the third pressure are
both below the first pressure; passing a natural gas feed stream
through at least a fourth heat exchanger pass of the plurality of
heat exchanger passes; and liquefying at least a portion of the
natural gas stream in the cold box using a refrigeration content
provided by at least one of the second refrigerant stream or the
third refrigerant stream to form an LNG stream.
[0069] A fifteenth aspect can include the method of the fourteenth
aspect, further comprising combining the second refrigerant stream
and the third refrigerant stream downstream of the cold box to form
a recycle stream; and compressing the recycle stream to form the
first refrigerant stream.
[0070] A sixteenth aspect can include the method of the fifteenth
aspect, wherein compressing the recycle stream comprises
compressing the recycle stream in a two-stage compressor.
[0071] A seventeenth aspect can include the method of the fifteenth
or sixteenth aspect, further comprising expanding the second
refrigerant stream to the second pressure in a first expander;
expanding the third refrigerant stream to the third pressure in a
second expander, wherein the second pressure is between about 20%
and about 50% of the first pressure on an absolute scale; and
compressing the third refrigerant stream prior to combining the
second refrigerant stream and the third refrigerant stream.
[0072] An eighteenth aspect can include the method of the
seventeenth aspect, wherein at least one of the first expander or
the second expander is coupled to a compressor, wherein compressing
the third refrigerant stream prior to combining the second
refrigerant stream and the third refrigerant stream comprises using
the compressor to compress the third refrigeration stream.
[0073] A nineteenth aspect can include the method of any of the
fourteenth to eighteenth aspects, wherein the second pressure is
between about 20% and about 50% of the first pressure on an
absolute scale.
[0074] A twentieth aspect can include the method of any of the
fourteenth to nineteenth aspects, wherein the third pressure is
between about 3% and about 20% of the first pressure on an absolute
scale.
[0075] Thus, specific embodiments and applications of small scale
LNG production and filling have been disclosed. It should be
apparent to those skilled in the art that many more modifications
besides those already described are possible without departing from
the concepts described herein. The present subject matter,
therefore, is not to be restricted except in the scope of the
appended claims. Moreover, in interpreting both the specification
and the claims, all terms should be interpreted in the broadest
possible manner consistent with the context. In particular, the
terms "comprises" and "comprising" should be interpreted as
referring to elements, components, or steps in a non-exclusive
manner, indicating that the referenced elements, components, or
steps may be present, utilized, or combined with other elements,
components, or steps that are not expressly referenced. Where the
specification or claims refers to at least one of something
selected from the group consisting of A, B, C . . . and N, the text
should be interpreted as requiring only one element from the group,
not A plus N, or B plus N, etc.
* * * * *