U.S. patent application number 15/229892 was filed with the patent office on 2017-02-09 for method for the integration of a nitrogen liquefier and liquefaction of natural gas for the production of liquefied natural gas and liquid nitrogen.
This patent application is currently assigned to L'Air Liquide, Societe Anonyme pour l'Etude et l'Exploitation des Procedes Georges Claude. The applicant listed for this patent is L'Air Liquide, Societe Anonyme pour l'Etude et l'Exploitation des Procedes Georges Claude. Invention is credited to Oriane FARGES, Alain GUILLARD, Michael A. TURNEY.
Application Number | 20170038136 15/229892 |
Document ID | / |
Family ID | 59215411 |
Filed Date | 2017-02-09 |
United States Patent
Application |
20170038136 |
Kind Code |
A1 |
TURNEY; Michael A. ; et
al. |
February 9, 2017 |
METHOD FOR THE INTEGRATION OF A NITROGEN LIQUEFIER AND LIQUEFACTION
OF NATURAL GAS FOR THE PRODUCTION OF LIQUEFIED NATURAL GAS AND
LIQUID NITROGEN
Abstract
A method for the integration of a nitrogen liquefier and
liquefaction of natural gas for the production of liquefied natural
gas and liquid nitrogen is provided. The method may include
providing a nitrogen liquefaction unit and providing a natural gas
liquefaction unit. Liquefaction of the nitrogen can be achieved via
a nitrogen refrigeration cycle within the nitrogen liquefaction
unit. Liquefaction of the natural gas can be achieved through the
use of natural gas letdown and a second nitrogen refrigeration
cycle. The two liquefaction units can be integrated via a common
nitrogen recycle compressor, thereby providing significant capital
savings.
Inventors: |
TURNEY; Michael A.;
(Houston, TX) ; FARGES; Oriane; (Houston, TX)
; GUILLARD; Alain; (Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
L'Air Liquide, Societe Anonyme pour l'Etude et l'Exploitation des
Procedes Georges Claude |
Paris |
|
FR |
|
|
Assignee: |
L'Air Liquide, Societe Anonyme pour
l'Etude et l'Exploitation des Procedes Georges Claude
Paris
FR
|
Family ID: |
59215411 |
Appl. No.: |
15/229892 |
Filed: |
August 5, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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62201947 |
Aug 6, 2015 |
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62305381 |
Mar 8, 2016 |
|
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62370953 |
Aug 4, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 1/0275 20130101;
F25J 2210/60 20130101; F25J 2215/64 20130101; F25J 2230/22
20130101; F25J 2270/08 20130101; F25J 2220/44 20130101; F25J 1/0092
20130101; F25J 1/0238 20130101; F25J 2220/64 20130101; F25J 1/0045
20130101; F25J 2230/42 20130101; F25J 2270/88 20130101; F25J 1/0202
20130101; F25J 2205/02 20130101; F25J 2270/42 20130101; F25J 1/004
20130101; F25J 1/0072 20130101; F25J 2245/42 20130101; F25J 2270/16
20130101; F25J 1/0007 20130101; F25J 1/0224 20130101; F25J 2230/60
20130101; F25J 2210/40 20130101; F25J 2220/66 20130101; F25J
2215/62 20130101; F25J 2220/60 20130101; F25J 2245/02 20130101;
F25J 1/001 20130101; F25J 1/0015 20130101; F25J 3/0257 20130101;
F25J 1/0271 20130101; F25J 1/0281 20130101; F25J 2270/14 20130101;
F25J 2210/06 20130101; F25J 1/0204 20130101; F25J 1/0292 20130101;
F25J 1/0236 20130101; F25J 1/0274 20130101; F25J 2205/04 20130101;
F25J 2215/42 20130101; F25J 2240/44 20130101; F25J 1/0037 20130101;
F25J 2240/40 20130101; F25J 2210/02 20130101; F25J 1/0052 20130101;
F25J 1/0288 20130101; F25J 2240/02 20130101; F25J 2290/34 20130101;
F25J 1/0208 20130101; F25J 2230/20 20130101; F25J 2290/70 20130101;
F25J 1/0232 20130101; F25J 1/0264 20130101; F25J 2220/02 20130101;
F25J 2220/68 20130101; F25J 3/04412 20130101; F25J 2230/30
20130101; F25J 2290/12 20130101; F25J 1/005 20130101; F25J 2240/12
20130101; F25J 1/0022 20130101 |
International
Class: |
F25J 1/02 20060101
F25J001/02; F25J 1/00 20060101 F25J001/00 |
Claims
1. A method for the integration of a nitrogen liquefier and natural
gas liquefier for the production of liquefied natural gas ("LNG")
and liquid nitrogen ("LIN"), the method comprising the steps of: a)
providing a nitrogen liquefier having a first nitrogen
refrigeration cycle, wherein the nitrogen liquefier comprises a
turbine, a booster and a plurality of coolers, wherein the first
nitrogen refrigeration cycle is configured to provide refrigeration
within a first heat exchanger; b) providing a second nitrogen
refrigeration cycle, wherein the second nitrogen refrigeration
cycle comprises a second turbine, a second booster and a plurality
of second coolers, wherein the second nitrogen refrigeration cycle
is configured to provide refrigeration within a second heat
exchanger; c) purifying a first natural gas stream in a first
purification unit to remove a first set of impurities to produce a
purified first natural gas stream; d) cooling and liquefying the
first natural gas stream in the second heat exchanger using the
refrigeration from the nitrogen refrigeration cycle to produce an
LNG stream, wherein the first natural gas stream has an LNG
refrigeration requirement, wherein the LNG stream is liquefied at a
first pressure P.sub.H; e) purifying a second natural gas stream in
a second purification unit to remove a second set of impurities to
produce a purified second natural gas stream; f) partially cooling
the second natural gas stream in the second heat exchanger; g)
withdrawing the partially cooled natural gas stream from an
intermediate section of the second heat exchanger; h) expanding the
partially cooled natural gas stream to a medium pressure P.sub.M in
a natural gas expansion turbine to form a cold natural gas stream,
wherein the medium pressure P.sub.M is at a pressure lower than the
first pressure P.sub.H; and i) warming the cold natural gas stream
in the second heat exchanger by heat exchange against the first
natural gas stream to produce a warm natural gas stream at the warm
end of the second heat exchanger, wherein the natural gas expansion
turbine drives a first booster, wherein the LNG refrigeration
requirement is supplied by a combination of refrigeration from the
second nitrogen refrigeration cycle and step i), wherein a portion
of the liquid nitrogen within the first nitrogen refrigeration
cycle is withdrawn as product liquid nitrogen, wherein at least an
equal portion of gaseous nitrogen is introduced to the first
nitrogen refrigeration cycle as is withdrawn as product liquid
nitrogen, and wherein the first nitrogen refrigeration cycle and
the second nitrogen refrigeration cycle share a common nitrogen
recycle compressor.
2. The method as claimed in claim 1, wherein the first booster is
configured to compress the second natural gas stream or a stream
derived from the second natural gas stream.
3. The method as claimed in claim 1, wherein the first booster is
configured to compress a stream selected from the group consisting
of the first natural gas stream, the purified first natural gas
stream, the second natural gas stream, the purified second natural
gas stream, the partially cooled natural gas stream, the warm
natural gas stream, and a nitrogen fluid within the nitrogen
refrigeration cycle.
4. The method as claimed in claim 1, wherein the first set of
impurities has a freezing point at or above the liquefaction
temperature of methane at the first pressure P.sub.H.
5. The method as claimed in claim 1, wherein the second set of
impurities comprises water.
6. The method as claimed in claim 1, wherein the first nitrogen
refrigeration cycle further comprises a nitrogen feed
compressor.
7. The method as claimed in claim 1, wherein the first nitrogen
refrigeration cycle is a closed refrigeration cycle.
8. The method as claimed in claim 1, wherein the first natural gas
stream and the second natural gas stream come from the same natural
gas source.
9. The method as claimed in claim 8, wherein the natural gas source
is a natural gas pipeline having a pressure between 15 and 100
bara.
10. The method as claimed in claim 1, wherein the first natural gas
stream comes from a first natural gas source, and the second
natural gas stream comes from a second natural gas source, wherein
the first and second natural gas sources are different sources.
11. The method as claimed in claim 10, wherein the first natural
gas source comprises a natural gas pipeline.
12. The method as claimed in claim 11, wherein the natural gas
pipeline has a pressure between 15 and 100 bara.
13. The method as claimed in claim 1, wherein the first
purification unit and the second purification unit are the same
unit.
14. The method as claimed in claim 1, wherein the first
purification unit and the second purification unit are separate
units, wherein the first purification unit is configured to remove
at least water and carbon dioxide, and wherein the second
purification unit is configured to remove at least water.
15. The method as claimed in claim 1, wherein the nitrogen
liquefier further comprises a subcooler.
16. A method for the integration of a first liquefier and a second
liquefier for the production of a first liquefied gas and a second
liquefied gas, the method comprising the steps of: a) providing a
first liquefier having a first refrigeration cycle, wherein the
first liquefier comprises a recycle compressor, a first heat
exchanger, and a turbine booster; b) providing a second
refrigeration cycle, wherein the second refrigeration cycle is
configured to provide refrigeration within a second heat exchanger,
c) cooling and liquefying a first gas stream in the second heat
exchanger by heat exchange with the second refrigeration cycle to
produce a liquefied first gas stream, wherein the liquefied first
gas stream is at a first pressure; d) expanding a second gas stream
to a second pressure to produce an expanded second gas stream; and
e) warming the expanded second gas stream in the second heat
exchanger to produce a warmed gas stream, wherein a portion of a
first refrigeration gas within the first refrigeration cycle is
withdrawn and liquefied yielding a liquid first refrigeration gas
product, wherein at least an equal portion of gaseous first
refrigeration gas is introduced to the first refrigeration cycle as
is withdrawn as liquid first refrigeration gas product, wherein
step e), in addition to the refrigeration provided by the second
refrigeration cycle, provides the refrigeration used to cool and
liquefy the first gas stream, and wherein the first refrigeration
cycle and the second refrigeration cycle share a common recycle
compressor.
17. The method as claimed in claim 16, wherein the first
refrigeration cycle is selected from the group consisting of a
nitrogen refrigeration cycle and a hydrogen refrigeration
cycle.
18. The method as claimed in claim 16, wherein the first gas stream
liquefied in step c) is derived from the expanded second gas
stream, wherein the first pressure and the second pressure are
about the same.
19. The method as claimed in claim 16, wherein the second
refrigeration cycle is selected from the group consisting of a
nitrogen refrigeration cycle and a hydrogen refrigeration
cycle.
20. The method as claimed in claim 16, wherein the first gas stream
cooled and liquefied in step c) comprises natural gas.
21. The method as claimed in claim 16, wherein the second gas
stream expanded in step d) comprises natural gas.
22. The method as claimed in claim 16, wherein the liquid first
refrigeration gas product is liquid nitrogen.
23. A method for the integration of a first liquefier and a second
liquefier for the production of a first liquefied gas and a second
liquefied gas, the method comprising the steps of: a) providing a
first liquefier having a first refrigeration cycle using a first
refrigerant, wherein the first refrigeration cycle is configured to
provide refrigeration within a first heat exchanger; b) providing a
second liquefier having a second refrigeration cycle using a second
refrigerant, wherein the second refrigeration cycle is configured
to provide refrigeration within a second heat exchanger; c) cooling
a first gas stream in the first heat exchanger by heat exchange
with the first refrigeration cycle to produce a cooled first gas
stream; d) cooling a second gas stream in the second heat exchanger
by heat exchange with the second refrigeration cycle to produce a
cooled second gas stream; e) expanding a third gas stream to
produce an expanded third gas stream; and f) warming the expanded
third gas stream in a heat exchanger selected from the group
consisting of the first heat exchanger, the second heat exchanger,
and combinations thereof, to produce a warmed gas stream, wherein
step f), in addition to the refrigeration provided by the second
refrigeration cycle, provides the refrigeration used to cool the
second gas stream, wherein step f), in addition to the
refrigeration provided by the first refrigeration cycle, provides
the refrigeration used to cool the first gas stream, and wherein
the first refrigeration cycle and the second refrigeration cycle
share a common recycle compressor.
24. The method as claimed in claim 23, wherein the first and second
refrigeration cycles are nitrogen refrigeration cycles.
25. The method as claimed in claim 23, wherein the first
refrigerant and the second refrigerant have the same
composition.
26. The method as claimed in claim 23, wherein the first gas stream
is selected from the group consisting of natural gas, ethane,
ethylene, acetylene, other C.sub.3-C.sub.6 alkanes, alkenes, and
alkynes, and nitrogen, and wherein the first gas stream is
liquefied during cooling step c).
27. The method as claimed in claim 23, wherein the first gas stream
is selected from the group consisting of hydrogen and helium,
wherein the first gas stream is not liquefied during cooling step
c).
28. The method as claimed in claim 23, wherein the third gas stream
expanded in step e) comprises natural gas.
29. The method as claimed in claim 23, wherein a portion of the
first refrigerant within the first refrigeration cycle is withdrawn
and liquefied yielding a liquid first refrigerant product, wherein
at least an equal portion of gaseous first refrigerant is
introduced to the first refrigeration cycle as is withdrawn as
liquid first refrigerant,
30. The method as claimed in claim 23, wherein a portion of the
second refrigerant within the second refrigeration cycle is
withdrawn and liquefied yielding a liquid second refrigerant,
wherein at least an equal portion of the second refrigerant is
introduced to the second refrigeration cycle as is withdrawn as
liquid second refrigerant.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 62/201,947, filed on Aug. 6, 2015, U.S.
Provisional Patent Application No. 62/305,381, filed on Mar. 8,
2016, and U.S. Provisional Application Ser. No. 62/370,953 filed on
Aug. 4, 2016, all of which are hereby incorporated by reference in
their entireties.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention generally relates to a method for
efficiently producing liquefied natural gas (LNG).
BACKGROUND OF THE INVENTION
[0003] Many locations utilize a high pressure (transmission)
network and a lower pressure (distribution) network to supply
natural gas through a local area. The transmission network
typically acts as a freeway to economically send the gas over long
distances to the general area, while the distribution network acts
as the roads to send the gas to the individual users within a local
area. Pressures of these networks vary by location, but typical
values are between 30-80 bara for transmission and 3-20 bara for
distribution. Some applications (e.g., cogeneration, boilers, etc.
. . . ) have high flowrates of natural gas and other utilities such
as nitrogen which are letdown to the consumer or to the lower
pressure network at relatively constant flow, pressure and
temperature conditions. This pressure letdown energy is often not
utilized.
[0004] Traditionally natural gas is compressed and sent down
pipelines under high pressure to transport the gas to market. High
pressures are used in order to reduce the volumetric flow of the
gas thereby reducing pipe diameters (capex) and/or compression
energy related to pressure losses (opex). Pipeline operators also
utilize the high pressure as a buffer to accommodate transient
demands. When the gas has arrived at its use point, the pressure of
the natural gas is reduced in one or more control valves to its
final pressure for consumption. The available energy from the
reduction in pressure of the natural gas is wasted in the control
valves as well as any chilling effect (also known as the Joule
Thomson effect) caused by the flow of natural gas through these
devices. Such systems often require heaters and condensate systems
due to the colder conditions of the downstream gas.
[0005] In the past, advantage has been taken of this wasted energy
by facilities utilizing the energy and refrigeration effect of
expanding the natural gas. One such facility was designed and
constructed by Airco Industrial Gases' Cryoplants Division in the
early 1970's in Reading, Pa. for UGI Corporation. It employed a
natural gas pressure reduction station ("Letdown Station") to make
liquefied natural gas ("LNG") or liquid nitrogen ("LIN"). A
majority of the natural gas entering the plant under high pressure
from the transportation pipeline was cooled and sent to an
expansion turbine where energy and refrigeration were generated.
The remainder of the stream was subsequently cooled with the
refrigeration and a portion liquefied. The liquefied portion was
then passed to a storage tank as LNG product. The natural gas that
was not liquefied was warmed, collected and sent to the low
pressure main at a lower pressure than the high-pressure main.
[0006] U.S. Pat. No. 6,196,021 describes a system that uses natural
gas expansion to provide refrigeration to liquefy a natural gas
stream which is then vaporized by heat exchange with a nitrogen
stream to cool the nitrogen stream. This refrigeration supplements
refrigeration provided by nitrogen pressure letdown and a nitrogen
cycle to provide liquid nitrogen. Similarly, U.S. Pat. No.
6,131,407 describes a system that produces LIN to be sent directly
to an air separation unit ("ASU") to assist refrigeration of the
ASU. U.S. Patent Application Publication No. 2014/0352353 describes
a similar system to the system of disclosed by U.S. Pat. No.
6,131,407, but adds that the LIN produced can be sent to a tank
instead of being used to liquid assist the ASU. In each of these
systems, LNG is revaporized to provide for nitrogen cooling.
However, it is not desirable to liquefy and then revaporize the
natural gas, as this is thermally inefficient. U.S. Pat. No.
6,694,774 describes a system that uses natural gas letdown to
provide refrigeration to produce a liquefied natural gas stream,
where the refrigeration is supplemented by a closed loop mixed
refrigerant cycle.
[0007] FIG. 1 provides a process flow diagram for a typical small
LNG scheme that utilizes a nitrogen cycle 50, which includes
nitrogen compressor 10, coolers 11, 21, 26, and first and second
turbine boosters 20, 25, in a closed loop. For purposes discussed
herein, a turbine booster is a combination of a turbine and a
booster, in which the booster is powered, at least partially, by
the turbine, which is typically accomplished via a common shaft.
Natural gas 2 is first purified of components that would damage
equipment or freeze during liquefaction in purification unit 30.
Purified natural gas 4 is then cooled in heat exchanger 40, where
it is condensed into LNG 6 using refrigeration provided by the
nitrogen refrigeration cycle 50. Typically, heavy hydrocarbons
(pentane and heavier) are removed from the natural gas either
before or from an intermediate location of the exchanger 40 by
adsorption, distillation or gas-liquid separator in order to
prevent these components from freezing in the exchanger 40. In the
example of FIG. 1 the natural gas 4 is withdrawn from an
intermediate section of the heat exchanger 40 in order to remove
the heavy hydrocarbons 8 using gas liquid separator 5. In the
typical setup shown of FIG. 1, the power required to produce 342
mtd of LNG is approximately 7155 kW, meaning the specific power of
this setup is approximately 502 kWh/mt.
[0008] Therefore, it would be advantageous to provide a method and
apparatus that operated in a more efficient manner yielding a lower
cost of LNG.
SUMMARY OF THE INVENTION
[0009] The present invention is directed to a method and apparatus
that satisfies at least one of these needs. In certain embodiments,
the invention can provide a lower cost, more efficient and flexible
method to produce LNG. For example, in certain embodiments, the
invention can also include coproduction of liquid nitrogen ("LIN").
In additional embodiments, the invention may include varying the
production rates of either or both the LIN and LNG, based on power
costs, product demand, and/or supply levels.
[0010] Nitrogen is transported through high pressure pipelines
because of the lower transport cost of reduced volumetric flows
associated with high pressure gas. Typically such pipelines operate
in the range of 30 to 50 bara. Customers using nitrogen from a
pipeline often do not need the nitrogen at these pressures. For
example, nitrogen is typically used as an inert utility fluid at
pressures in range of 3 to 8 bara. As such, in these locations,
potential refrigeration capacity is wasted. Additionally, there are
instances in which producers of the nitrogen gas feeding the
pipeline do not operate at 100% of equipment design capacity, and
therefore, large nitrogen compressors are either not operating or
not operating at optimum capacity. This can occur if the demand for
nitrogen is lower than originally anticipated, for example. Another
reason this occurs is because the nitrogen producing equipment is
sized to meet peak customer demand under peak operating scenarios,
ambient conditions, catalyst life, and the like. As such, the
nitrogen producing equipment may be designed to be underutilized
during many operating scenarios when other systems are not able to
accommodate increased loads.
[0011] In certain embodiments of the invention, a process can
provide for LNG and/or LIN production with at least reduced energy
input by using the refrigeration capabilities of letdown of natural
gas and let down of nitrogen or a gas rich in nitrogen. An example
of a gas rich in nitrogen is a lean synthetic air stream with less
than 12% O.sub.2 (e.g., due to the limit of combustion for a
mixture with methane). In embodiments, the letdown process occurs
at a location that is proximate to an existing facility or location
where the letdown of both natural gas and nitrogen occurs to serve
the needs of the facility, such that LNG and/or LIN can be produced
with reduced operating costs and/or capital costs as compared to a
situation without the benefit of the letdown of a gas stream (e.g.,
a nitrogen stream, a stream of gas rich in nitrogen, or a natural
gas or other high pressure gas stream at a production site).
[0012] In one embodiment, the invention can include a method for
the production of liquefied natural gas ("LNG"). In one embodiment,
the method can include the steps of: a) providing a nitrogen
refrigeration cycle, wherein the nitrogen refrigeration cycle is
configured to provide refrigeration within a heat exchanger; b)
purifying a first natural gas stream in a first purification unit
to remove a first set of impurities to produce a purified first
natural gas stream; c) cooling and liquefying the first natural gas
stream in the heat exchanger using the refrigeration from the
nitrogen refrigeration cycle to produce an LNG stream, wherein the
first natural gas stream has an LNG refrigeration requirement,
wherein the LNG stream is liquefied at a first pressure P.sub.H; d)
purifying a second natural gas stream in a second purification unit
to remove a second set of impurities to produce a purified second
natural gas stream; e) partially cooling the second natural gas
stream in the heat exchanger; f) withdrawing the partially cooled
second natural gas stream from an intermediate section of the heat
exchanger; g) expanding the partially cooled second natural gas
stream to a medium pressure P.sub.M in a natural gas expansion
turbine to form a cold natural gas stream, wherein the medium
pressure P.sub.M is at a pressure lower than the first pressure
P.sub.H; and h) warming the cold natural gas stream in the heat
exchanger by heat exchange against the first natural gas stream to
produce a warm natural gas stream at the warm end of the heat
exchanger, wherein the natural gas expansion turbine drives a first
booster, wherein the LNG refrigeration requirement is supplied by a
combination of refrigeration from the nitrogen refrigeration cycle
and step h).
[0013] In optional embodiments of the method for the production of
LNG: [0014] the first booster is configured to compress the second
natural gas stream or a stream derived from the second natural gas
stream; [0015] the first booster is configured to compress a stream
selected from the group consisting of the first natural gas stream,
the first purified natural gas stream, the second natural gas
stream, the purified second natural gas stream, the partially
cooled natural gas stream, the warm natural gas stream, and a
nitrogen fluid within the nitrogen refrigeration cycle; [0016] the
first set of impurities has a freezing point at or above the
liquefaction temperature of methane at the first pressure P.sub.H;
[0017] the second set of impurities comprises water; [0018] the
nitrogen refrigeration cycle comprises a recycle compressor, a
turbine, a booster and a plurality of coolers, wherein the turbine
and booster are configured such that the turbine is configured to
power the booster; [0019] the first natural gas stream and the
second natural gas stream come from the same natural gas source;
[0020] the natural gas source is a natural gas pipeline having a
pressure between 15 and 100 bara; [0021] the first natural gas
stream comes from a first natural gas source, and the second
natural gas stream comes from a second natural gas source, wherein
the first and second natural gas sources are different sources;
[0022] the first natural gas source comprises a natural gas
pipeline; [0023] the natural gas pipeline has a pressure between 15
and 100 bara; [0024] the first purification unit and the second
purification unit are the same unit; and/or [0025] the first
purification unit and the second purification unit are separate
units, wherein the first purification unit is configured to remove
at least water and carbon dioxide, and wherein the second
purification unit is configured to remove at least water.
[0026] In another aspect of the invention, a method for the
production of liquefied natural gas ("LNG") is provided. In this
embodiment, the method comprising the steps of: a) providing a
nitrogen refrigeration cycle; b) cooling and liquefying a first
natural gas stream in a heat exchanger by heat exchange with
nitrogen from the nitrogen refrigeration cycle to produce an LNG
stream, wherein the LNG stream is liquefied at a first pressure; c)
expanding a second natural gas stream to a second pressure to
produce an expanded natural gas stream; and d) warming the expanded
natural gas stream in the heat exchanger to produce a warmed
natural gas stream, wherein step d) provides a portion of the
refrigeration used to cool and liquefy the first natural gas
stream.
[0027] In optional embodiments of the method for the production of
LNG: [0028] the first natural gas stream comes from a first natural
gas source, and the second natural gas stream comes from a second
natural gas source, wherein the first and second natural gas
sources are different sources; and/or [0029] the first natural gas
liquefied in step b) is derived from the expanded natural gas
stream, wherein the first pressure and the second pressure are
about the same.
[0030] In another aspect of the invention, a method for the
production of liquefied natural gas ("LNG") is provided. In this
embodiment, the method comprising the steps of a) providing a high
pressure natural gas stream; b) splitting the high pressure natural
gas stream into a first portion and a second portion; c) cooling
and liquefying the first portion of the high pressure natural gas
stream to produce an LNG stream; d) providing a first portion of
refrigeration via a nitrogen refrigeration cycle, wherein the
nitrogen refrigeration cycle comprises a recycle compressor, a
turbine, a booster and a plurality of coolers, wherein the turbine
and booster are configured such that the turbine is configured to
power the booster; e) providing a second portion of refrigeration
by expanding the second portion of the high pressure natural gas;
and f) using the first portion of refrigeration and the second
portion of refrigeration to achieve the cooling and liquefaction of
the first portion of the high pressure natural gas stream in step
c).
[0031] In another aspect of the invention, a method for the
production of liquefied natural gas ("LNG") and liquid nitrogen
("LIN") is provided. In this embodiment, the method can include the
steps of: a) providing a nitrogen refrigeration cycle, wherein the
nitrogen refrigeration cycle is configured to provide refrigeration
within a heat exchanger, wherein a portion of the nitrogen within
the nitrogen refrigeration cycle is withdrawn and liquefied
yielding a liquid nitrogen product, wherein at least an equal
portion of gaseous nitrogen is introduced to the nitrogen
refrigeration cycle as is withdrawn; b) purifying a first natural
gas stream in a first purification unit to remove a first set of
impurities to produce a purified first natural gas stream; c)
cooling and liquefying the first natural gas stream in the heat
exchanger using the refrigeration from the nitrogen refrigeration
cycle to produce an LNG stream, wherein the first natural gas
stream has an LNG refrigeration requirement, wherein the LNG stream
is liquefied at a first pressure P.sub.H; d) purifying a second
natural gas stream in a second purification unit to remove a second
set of impurities to produce a purified second natural gas stream;
e) partially cooling the second natural gas stream in the heat
exchanger; f) withdrawing the partially cooled second natural gas
stream from an intermediate section of the heat exchanger; g)
expanding the partially cooled second natural gas stream to a
medium pressure P.sub.M in a natural gas expansion turbine to form
a cold natural gas stream, wherein the medium pressure P.sub.M is
at a pressure lower than the first pressure P.sub.H; and h) warming
the cold natural gas stream in the heat exchanger by heat exchange
against the first natural gas stream to produce a warm natural gas
stream at the warm end of the heat exchanger, wherein the natural
gas expansion turbine drives a first booster, wherein the LNG
refrigeration requirement is supplied by a combination of
refrigeration from the nitrogen refrigeration cycle and step
h).
[0032] In optional embodiments of the method for the production of
LNG and LIN: [0033] the first booster is configured to compress the
second natural gas stream or a stream derived from the second
natural gas stream; [0034] the first booster is configured to
compress a stream selected from the group consisting of the first
natural gas stream, the purified first natural gas stream; the
second natural gas stream, the purified second natural gas stream,
the partially cooled natural gas stream, the warm natural gas
stream, and a nitrogen fluid within the nitrogen refrigeration
cycle; [0035] the liquid nitrogen product has a LIN refrigeration
requirement, wherein the LIN refrigeration requirement is supplied
by a combination of refrigeration from the nitrogen refrigeration
cycle and step h); [0036] the first set of impurities has a
freezing point at or above the liquefaction temperature of methane
at the first pressure P.sub.H; [0037] the second set of impurities
comprises water; [0038] the nitrogen refrigeration cycle comprises
a recycle compressor, a turbine, a booster and a plurality of
coolers, wherein the turbine and booster are configured such that
the turbine is configured to power the booster; [0039] the nitrogen
refrigeration cycle further comprises a nitrogen feed compressor;
[0040] the first natural gas stream and the second natural gas
stream come from the same natural gas source; [0041] the natural
gas source is a natural gas pipeline having a pressure between 15
and 100 bara; [0042] the first natural gas stream comes from a
first natural gas source, and the second natural gas stream comes
from a second natural gas source, wherein the first and second
natural gas sources are different sources; [0043] the first natural
gas source comprises a natural gas pipeline; [0044] the natural gas
pipeline has a pressure between 15 and 100 bara; [0045] the first
purification unit and the second purification unit are the same
unit; [0046] the first purification unit and the second
purification unit are separate units, wherein the first
purification unit is configured to remove at least water and carbon
dioxide, and wherein the second purification unit is configured to
remove at least water; and/or [0047] the nitrogen liquefier further
comprises a subcooler.
[0048] In another aspect of the invention, a method for the
production of liquefied natural gas ("LNG") and liquid nitrogen
("LIN") is provided. In this embodiment, the method can include the
steps of: a) providing a nitrogen refrigeration cycle, wherein the
nitrogen refrigeration cycle is configured to provide refrigeration
within a heat exchanger, wherein a portion of the nitrogen within
the nitrogen refrigeration cycle is withdrawn and liquefied
yielding a liquid nitrogen product, wherein at least an equal
portion of gaseous nitrogen is introduced to the nitrogen
refrigeration cycle as is withdrawn; b) cooling and liquefying a
first natural gas stream in a heat exchanger by heat exchange with
nitrogen from the nitrogen refrigeration cycle to produce an LNG
stream, wherein the LNG stream is liquefied at a first pressure; c)
expanding a second natural gas stream to a second pressure to
produce an expanded natural gas stream; and d) warming the expanded
natural gas stream in the heat exchanger to produce a warmed
natural gas stream, wherein step d) provides a portion of the
refrigeration used to cool and liquefy the first natural gas
stream.
[0049] In optional embodiments of the method for the production of
LNG and LIN: [0050] the first natural gas stream comes from a first
natural gas source, and the second natural gas stream comes from a
second natural gas source, wherein the first and second natural gas
sources are different sources; [0051] the liquid nitrogen product
has a LIN refrigeration requirement, wherein the LIN refrigeration
requirement is supplied by a combination of refrigeration from the
nitrogen refrigeration cycle and step d); and/or [0052] the first
natural gas liquefied in step b) is derived from the expanded
natural gas stream, wherein the first pressure and the second
pressure are about the same.
[0053] In another aspect of the invention, a method for the
production of liquefied natural gas ("LNG") and liquid nitrogen
("LIN") is provided. In this embodiment, the method can include the
steps of: a) providing a nitrogen refrigeration cycle, wherein the
nitrogen refrigeration cycle comprises a recycle compressor, a
turbine, a booster and a plurality of coolers, wherein the turbine
and booster are configured such that the turbine is configured to
power the booster, wherein a portion of the nitrogen within the
nitrogen refrigeration cycle is withdrawn and liquefied yielding a
liquid nitrogen product, wherein at least an equal portion of
gaseous nitrogen is introduced to the nitrogen refrigeration cycle
as is withdrawn; b) providing a high pressure natural gas stream;
c) splitting the high pressure natural gas stream into a first
portion and a second portion; d) cooling and liquefying the first
portion of the high pressure natural gas stream to produce an LNG
stream; e) providing a first portion of refrigeration via the
nitrogen refrigeration cycle; f) providing a second portion of
refrigeration by expanding the second portion of the high pressure
natural gas; and g) using the first portion of refrigeration and
the second portion of refrigeration to achieve the cooling and
liquefaction of the first portion of the high pressure natural gas
stream in step d).
[0054] In another aspect of the invention, a method for the
integration of a nitrogen liquefier and natural gas liquefier for
the production of liquefied natural gas ("LNG") and liquid nitrogen
("LIN") is provided. In this embodiment, the method can include the
steps of: a) providing a nitrogen liquefier having a first nitrogen
refrigeration cycle, wherein the nitrogen liquefier comprises a
turbine, a booster and a plurality of coolers, wherein the first
nitrogen refrigeration cycle is configured to provide refrigeration
within a first heat exchanger; b) providing a second nitrogen
refrigeration cycle, wherein the second nitrogen refrigeration
cycle comprises a second turbine, a second booster and a plurality
of second coolers, wherein the second nitrogen refrigeration cycle
is configured to provide refrigeration within a second heat
exchanger; c) purifying a first natural gas stream in a first
purification unit to remove a first set of impurities to produce a
purified first natural gas stream; d) cooling and liquefying the
first natural gas stream in the second heat exchanger using the
refrigeration from the nitrogen refrigeration cycle to produce an
LNG stream, wherein the first natural gas stream has an LNG
refrigeration requirement, wherein the LNG stream is liquefied at a
first pressure P.sub.H; e) purifying a second natural gas stream in
a second purification unit to remove a second set of impurities to
produce a purified second natural gas stream; f) partially cooling
the second natural gas stream in the second heat exchanger; g)
withdrawing the partially cooled natural gas stream from an
intermediate section of the second heat exchanger; h) expanding the
partially cooled natural gas stream to a medium pressure P.sub.M in
a natural gas expansion turbine to form a cold natural gas stream,
wherein the medium pressure P.sub.M is at a pressure lower than the
first pressure P.sub.H; and i) warming the cold natural gas stream
in the second heat exchanger by heat exchange against the first
natural gas stream to produce a warm natural gas stream at the warm
end of the second heat exchanger, wherein the natural gas expansion
turbine drives a first booster, wherein the LNG refrigeration
requirement is supplied by a combination of refrigeration from the
second nitrogen refrigeration cycle and step i), wherein a portion
of the liquid nitrogen within the first nitrogen refrigeration
cycle is withdrawn as product liquid nitrogen, wherein at least an
equal portion of gaseous nitrogen is introduced to the first
nitrogen refrigeration cycle as is withdrawn as product liquid
nitrogen, and wherein the first nitrogen refrigeration cycle and
the second nitrogen refrigeration cycle share a common nitrogen
recycle compressor.
[0055] In optional embodiments of the method integration of a
nitrogen liquefier and natural gas liquefier: [0056] the first
booster is configured to compress the second natural gas stream or
a stream derived from the second natural gas stream; [0057] the
first booster is configured to compress a stream selected from the
group consisting of the first natural gas stream, the purified
first natural gas stream, the second natural gas stream, the
purified second natural gas stream, the partially cooled natural
gas stream, the warm natural gas stream, and a nitrogen fluid
within the nitrogen refrigeration cycle; the first set of
impurities has a freezing point at or above the liquefaction
temperature of methane at the first pressure P.sub.H; [0058] the
second set of impurities comprises water; [0059] the first nitrogen
refrigeration cycle further comprises a nitrogen feed compressor;
[0060] the first nitrogen refrigeration cycle is a closed
refrigeration cycle; [0061] the first natural gas stream and the
second natural gas stream come from the same natural gas source;
[0062] the natural gas source is a natural gas pipeline having a
pressure between 15 and 100 bara; [0063] the first natural gas
stream comes from a first natural gas source, and the second
natural gas stream comes from a second natural gas source, wherein
the first and second natural gas sources are different sources;
[0064] the first natural gas source comprises a natural gas
pipeline; [0065] the natural gas pipeline has a pressure between 15
and 100 bara; [0066] the first purification unit and the second
purification unit are the same unit; [0067] the first purification
unit and the second purification unit are separate units, wherein
the first purification unit is configured to remove at least water
and carbon dioxide, and wherein the second purification unit is
configured to remove at least water; and/or [0068] the nitrogen
liquefier further comprises a subcooler.
[0069] In another aspect of the invention, a method for the
integration of a first liquefier and a second liquefier for the
production of first liquefied gas and a second liquefied gas is
provided. In this embodiment, the method can include the steps of:
a) providing a first liquefier having a first refrigeration cycle,
wherein the first liquefier comprises a recycle compressor, a first
heat exchanger, and a turbine booster; b) providing a second
refrigeration cycle, wherein the second refrigeration cycle is
configured to provide refrigeration within a second heat exchanger,
c) cooling and liquefying a first gas stream in the second heat
exchanger by heat exchange with the second refrigeration cycle to
produce a liquefied first gas stream, wherein the liquefied first
gas stream is at a first pressure; d) expanding a second gas stream
to a second pressure to produce an expanded second gas stream; and
e) warming the expanded second gas stream in the second heat
exchanger to produce a warmed gas stream, wherein a portion of a
first refrigeration gas within the first refrigeration cycle is
withdrawn and liquefied yielding a liquid first refrigeration gas
product, wherein at least an equal portion of gaseous first
refrigeration gas is introduced to the first refrigeration cycle as
is withdrawn as liquid first refrigeration gas product, wherein
step e), in addition to the refrigeration provided by the second
refrigeration cycle, provides the refrigeration used to cool and
liquefy the first gas stream, and wherein the first refrigeration
cycle and the second refrigeration cycle share a common recycle
compressor.
[0070] In optional embodiments of the method for the integration of
a first liquefier and a second liquefier: [0071] the first
refrigeration cycle is selected from the group consisting of a
nitrogen refrigeration cycle and a hydrogen refrigeration cycle;
[0072] the first gas stream liquefied in step c) is derived from
the expanded second gas stream, wherein the first pressure and the
second pressure are about the same; [0073] the second refrigeration
cycle is selected from the group consisting of a nitrogen
refrigeration cycle and a hydrogen refrigeration cycle; [0074] the
first gas stream cooled and liquefied in step c) comprises natural
gas; [0075] the second gas stream expanded in step d) comprises
natural gas; and/or [0076] the liquid first refrigeration gas
product is liquid nitrogen.
[0077] In another aspect of the invention, a method for the
integration of a first liquefier and a second liquefier for the
production of a first liquefied gas and a second liquefied gas is
provided. In this embodiment, the method can include the steps of:
a) providing a first liquefier having a first refrigeration cycle
using a first refrigerant, wherein the first refrigeration cycle is
configured to provide refrigeration within a first heat exchanger;
b) providing a second liquefier having a second refrigeration cycle
using a second refrigerant, wherein the second refrigeration cycle
is configured to provide refrigeration within a second heat
exchanger; c) cooling a first gas stream in the first heat
exchanger by heat exchange with the first refrigeration cycle to
produce a cooled first gas stream; d) cooling a second gas stream
in the second heat exchanger by heat exchange with the second
refrigeration cycle to produce a cooled second gas stream; e)
expanding a third gas stream to produce an expanded third gas
stream; and f) warming the expanded third gas stream in a heat
exchanger selected from the group consisting of the first heat
exchanger, the second heat exchanger, and combinations thereof, to
produce a warmed gas stream, wherein step f), in addition to the
refrigeration provided by the second refrigeration cycle, provides
the refrigeration used to cool the second gas stream, wherein step
f), in addition to the refrigeration provided by the first
refrigeration cycle, provides the refrigeration used to cool the
first gas stream, and wherein the first refrigeration cycle and the
second refrigeration cycle share a common recycle compressor.
[0078] In optional embodiments of the method for the integration of
a first liquefier and a second liquefier: [0079] the first and
second refrigeration cycles are nitrogen refrigeration cycles;
[0080] the first refrigerant and the second refrigerant have the
same composition; [0081] the first gas stream is selected from the
group consisting of natural gas, ethane, ethylene, acetylene, other
C3-C6 alkanes, alkenes, and alkynes, and nitrogen, and wherein the
first gas stream is liquefied during cooling step c); [0082] the
first gas stream is selected from the group consisting of hydrogen
and helium, wherein the first gas stream is not liquefied during
cooling step c); [0083] the third gas stream expanded in step e)
comprises natural gas; [0084] a portion of the first refrigerant
within the first refrigeration cycle is withdrawn and liquefied
yielding a liquid first refrigerant product, wherein at least an
equal portion of gaseous first refrigerant is introduced to the
first refrigeration cycle as is withdrawn as liquid first
refrigerant; and/or [0085] a portion of the second refrigerant
within the second refrigeration cycle is withdrawn and liquefied
yielding a liquid second refrigerant, wherein at least an equal
portion of the second refrigerant is introduced to the second
refrigeration cycle as is withdrawn as liquid second
refrigerant.
[0086] In another aspect of the invention, a method for the
integration of a nitrogen liquefier and letdown of natural gas for
the production liquid nitrogen ("LIN") is provided. In this
embodiment, the method can include the steps of: a) providing a
nitrogen liquefier having a nitrogen refrigeration cycle, wherein
the nitrogen liquefier comprises a nitrogen recycle compressor, a
heat exchanger, and a first turbine booster; b) introducing a
nitrogen gas stream to the nitrogen liquefier under conditions
effective for liquefying the nitrogen to produce a liquid nitrogen
product; c) withdrawing a natural gas stream from a source
operating at a first pressure P.sub.H; d) purifying the natural gas
stream in a purification unit to produce a purified natural gas; e)
partially cooling the purified natural gas in the heat exchanger;
f) withdrawing the partially cooled natural gas from an
intermediate section of the heat exchanger; g) expanding the
partially cooled natural gas to a medium pressure P.sub.M in a
natural gas expansion turbine to form a cold natural gas stream,
wherein the medium pressure P.sub.M is at a pressure lower than the
first pressure P.sub.H; and h) warming the cold natural gas stream
in the heat exchanger by heat exchange against nitrogen from the
nitrogen refrigeration cycle to produce a warm natural gas stream
from a warm end of the heat exchanger, wherein step h) provides
additional refrigeration to the nitrogen liquefier such that
additional liquid nitrogen can be produced as compared to a method
having an absence of steps c)-i), wherein the natural gas expansion
turbine drives a first gas booster.
[0087] In optional embodiments of the method for the integration of
a nitrogen liquefier and letdown of a natural gas stream: [0088]
the first gas booster is configured to compress the natural gas
stream or a stream derived therefrom; [0089] the first gas booster
is configured to compress a stream selected from the group
consisting of the natural gas stream, the purified natural gas
stream, the partially cooled natural gas stream, the warm natural
gas stream, and a nitrogen fluid within the nitrogen refrigeration
cycle; [0090] the purification unit is configured to remove at
least water from the natural gas stream; [0091] the nitrogen
refrigeration cycle further comprises a nitrogen feed compressor;
[0092] the nitrogen liquefier further comprises a subcooler; [0093]
the source of the natural gas comprises a natural gas pipeline;
and/or [0094] the natural gas pipeline has a pressure between 15
and 100 bara.
[0095] In another aspect of the invention, a method for integration
of a nitrogen liquefier and letdown of natural gas for the
production of liquid nitrogen ("LIN") is provided. In this
embodiment, the method can include the steps of: a) providing a
nitrogen liquefier having a nitrogen refrigeration cycle, wherein
the nitrogen liquefier comprises a nitrogen recycle compressor, a
heat exchanger, and at least one turbine booster; b) introducing a
nitrogen gas stream to the nitrogen liquefier under conditions
effective for liquefying the nitrogen to produce a liquid nitrogen
product; c) recovering a natural gas stream from a high pressure
source, wherein the natural gas stream is at a first pressure; d)
expanding the natural gas stream to a second pressure to produce an
expanded natural gas stream, wherein the second pressure is a
pressure that is lower than the first pressure; and e) warming the
expanded natural gas stream in the heat exchanger to produce a
warmed natural gas stream, wherein step e) provides additional
refrigeration to the nitrogen liquefier such that additional liquid
nitrogen can be produced as compared to a method having an absence
of steps d) through e).
BRIEF DESCRIPTION OF THE DRAWINGS
[0096] These and other features, aspects, and advantages of the
present invention will become better understood with regard to the
following description, claims, and accompanying drawings. It is to
be noted, however, that the drawings illustrate only several
embodiments of the invention and are therefore not to be considered
limiting of the invention's scope as it can admit to other equally
effective embodiments.
[0097] FIG. 1 provides an embodiment of the prior art.
[0098] FIG. 2 provides an embodiment of the present invention.
[0099] FIG. 3 provides an embodiment of the present invention with
both LIN and LNG production.
[0100] FIG. 4 provides another embodiment of the present invention
with both LIN and LNG production.
[0101] FIG. 5 provides an embodiment of the present invention with
LIN and medium pressure natural gas production.
DETAILED DESCRIPTION
[0102] While the invention will be described in connection with
several embodiments, it will be understood that it is not intended
to limit the invention to those embodiments. On the contrary, it is
intended to cover all the alternatives, modifications and
equivalence as may be included within the spirit and scope of the
invention defined by the appended claims.
[0103] In one embodiment, the method can include integrating a
natural gas letdown system with a nitrogen refrigeration cycle. In
one embodiment, the nitrogen refrigeration cycle is a closed loop
refrigeration cycle. In this embodiment, the natural gas letdown
essentially provides "free" refrigeration energy since the natural
gas would have been alternatively letdown across a valve (i.e., the
resulting drop in temperature of the natural gas would have been
absorbed by the surroundings and would not have been recovered in
any meaningful way). With the addition of a natural gas turbine
booster, LNG can be co-produced with a significant power savings,
while also potentially reducing the size of the nitrogen
refrigeration cycle. In another embodiment, a purification unit,
storage, loading and utility systems may also be included.
[0104] Referring to FIG. 2, a process flow diagram of an embodiment
of the current invention is shown. In FIG. 2, high pressure natural
gas 2 is preferably split into two portions, with one portion being
liquefied and the other portion providing a portion of the
refrigeration used to cool and liquefy the natural gas. First
portion of the natural gas stream 102 is purified in first
purification unit 130, wherein acid gases, water and mercury are
preferably removed. Preferably, any impurity within the natural gas
that would solidify prior to the natural gas liquefying or damage
the downstream equipments is removed in first purification unit
130. The resulting purified first portion of the natural gas stream
104 is then withdrawn from first purification unit 130 and
introduced to heat exchanger 40 for liquefaction therein. In
embodiments in which the natural gas feed contains heavy
hydrocarbons, it is preferable to withdraw purified first portion
of the natural gas 104 from an intermediate section of heat
exchanger 40 and separate the heavy hydrocarbons 8 using gas liquid
separator 5. Alternatively, the gas-liquid separator may be
replaced by a distillation column or other separation devices known
in the art. Instead of collecting heavy hydrocarbons 8 separately
as shown in FIG. 1, heavy hydrocarbons 8 may be expanded and then
warmed in heat exchanger 40. The resulting warmed stream can be
combined with other natural gas streams (e.g., cold natural gas
stream 144 and first portion of the LNG 146) within heat exchanger
40. This advantageously captures some of the cold energy from heavy
hydrocarbons 8, and if warm natural gas stream 108 is subsequently
used for fuel, it also provides additional energy for that
purpose.
[0105] Vaporized natural gas from gas liquid separator 5 is
reintroduced to heat exchanger 40, wherein it subsequently
liquefies to produce LNG 6. In one embodiment, first portion of the
LNG 146 can be removed from LNG 6, expanded in second valve V2, and
then warmed in heat exchanger 40, thereby providing additional
refrigeration, to produce warm natural gas stream 108. The
remaining portion can then be expanded across third valve V3,
thereby producing low pressure LNG 148.
[0106] Refrigeration for the system is provided by two sources. The
first refrigeration source can be via a conventional nitrogen
refrigeration cycle 50. Nitrogen gas is compressed in nitrogen
recycle compressor 10, cooled in cooler 11, compressed further in
booster of first turbine booster 20, cooled in cooler 21, then
further compressed in booster of second turbine booster 25 before
being cooled again in cooler 26. The resulting compressed nitrogen
is then cooled in heat exchanger 40, wherein a first portion is
removed and expanded in turbine of second turbine booster 25 and
the remaining portion is removed and expanded in turbine of first
turbine booster 20. The resulting expanded nitrogen streams are
then introduced to heat exchanger 40, where they are warmed via
indirect heat exchange against the natural gas and other nitrogen
streams.
[0107] The second refrigeration source is provided by using the
excess pressure differential of the high pressure natural gas. In
this embodiment, second portion of the natural gas stream 106 is
split from high pressure natural gas 2, and then purified in second
purification unit 131 of at least water and potentially mercury to
produce purified second portion of the natural gas 132. While the
embodiment shown in FIG. 2 includes two separate purification
units, it is possible to use a single purification unit to fully
purify the entire natural gas stream prior to splitting the natural
gas into two streams. However, it is preferable to split the
streams prior to purification since the natural gas used to provide
refrigeration (i.e., the portion not liquefied), does not need to
have carbon dioxide removed, since the natural gas turbine outlet
stream 144 is at a sufficiently warm temperature such that carbon
dioxide will not freeze within this stream. In another embodiment,
units 130 and 131 may be combined into a single unit, and the
moisture free stream (e.g., 132) is removed at an intermediate
location of the vessel and the moisture and CO.sub.2 free stream
(e.g., 104) is removed from the end of the vessel opposite the feed
location.
[0108] Purified second portion of the natural gas 132 is then
compressed in booster of natural gas turbine booster 120, cooled in
cooler 140 to produce compressed natural gas stream 142. Compressed
natural gas stream 142 can then be partially cooled in heat
exchanger 40, before being expanded in turbine of natural gas
turbine booster 120 to form cold natural gas stream 144.
Alternatively, in an embodiment not shown, natural gas stream 142
can be sent, prior to cooling, directly to natural gas turbine 120
for expansion. This can help limit the temperature of 144 to avoid
heavy hydrocarbon condensation and potential solidification. Cold
natural gas stream 144 is then reintroduced to heat exchanger 40,
wherein it is warmed via indirect heat exchange and collected as
warm natural gas stream 108 from the warm end of the heat
exchanger. In one embodiment, cold natural gas stream 144 can be
combined with heavy hydrocarbons 8 and optionally first portion of
the LNG 146 within the heat exchanger, or the different streams can
warm individually within the heat exchanger and be combined
following their warming.
[0109] The booster of natural gas turbine booster 120 can be
located at many different locations depending on the natural gas
source and return pressures. For example, it may be located at 1)
the NG stream to be expanded (FIG. 2) if the feed pressure and/or
return pressure are low, 2) the total natural gas feed flow before
splitting the flow to be expanded and flow to be liquefied (FIG.
3), or 3) on the discharge of the turbine at the warm end of the
exchanger (e.g., stream 108) in the case of high natural gas feed
pressure and high natural return pressure (not shown), or 4) on the
natural gas stream to be liquefied (e.g., stream 104) if the feed
pressure is low (not shown). Alternatively the turbine may be used
to drive an electrical generator or dissipated by oil brake (not
shown).
[0110] A comparison of the embodiment shown in FIGS. 1 and 2 can be
found in Table I below:
TABLE-US-00001 TABLE I Comparison of Energy Requirements for FIG. 1
and FIG. 2 Base (Typical LNG LNG production by production by N2 NG
letdown and N2 cycle) FIG. 1 cycle. FIG. 2 NG supply 32 bara 342
1019 (mtd) NG to letdown 5.6 0 677 bara (mtd) LNG Production 342
342 (mtd) N2 cycle power input 7155 4158 (kW) LNG Specific power
502 292 (kWh/mt) Power Reduction (%) -- 42% LIN production -- --
(mtd) LIN Specific Power -- -- (kWh/mt)
[0111] In the setup shown of FIG. 2, the power required to produce
342 mtd of LNG is reduced to approximately 4158 kW, meaning the
specific power of this setup is approximately 292 kWh/mt. As such,
this represents a decrease of approximately 42% in power
requirements.
[0112] Regarding FIG. 3, a process flow diagram of an embodiment
for the co-production of liquid nitrogen and LNG using a nitrogen
refrigeration cycle in combination with natural gas letdown. In
FIG. 3, natural gas can be acquired from a natural gas source,
compressed in natural gas booster 101 to produce high pressure
natural gas 2. High pressure natural gas 2 is preferably split into
two portions, with one portion being liquefied and the other
portion providing a portion of the refrigeration used to cool and
liquefy the natural gas. First portion of the natural gas stream
102 is purified in first purification unit 130, wherein acid gases,
water and mercury are preferably removed. Preferably, any impurity
within the natural gas that would damage or solidify prior to the
natural gas liquefying is removed in first purification unit 130.
The resulting purified first portion of the natural gas stream 104
is then withdrawn from first purification unit 130 and introduced
to heat exchanger 40 for liquefaction therein. In embodiments in
which the natural gas feed contains heavy hydrocarbons, it is
preferable to withdraw purified first portion of the natural gas
104 from an intermediate section of heat exchanger 40 and separate
the heavy hydrocarbons 8 using gas liquid separator 5.
Alternatively, the gas-liquid separator may be replaced by a
distillation column or other separation devices known in the art.
Instead of collecting heavy hydrocarbons 8 separately as shown in
FIG. 1, heavy hydrocarbons 8 may be expanded and then warmed in
heat exchanger 40. The resulting warmed stream can be combined with
cold natural gas stream 144 within heat exchanger 40. This
advantageously captures some of the cold energy from heavy
hydrocarbons 8, and if warm natural gas stream 108 is subsequently
used for fuel, it also provides additional energy for that
purpose.
[0113] Vaporized natural gas from gas liquid separator 5 is
reintroduced to heat exchanger 40, wherein it subsequently
liquefies to produce LNG 6. While not shown specifically in FIG. 3,
as in FIG. 2, in one embodiment, first portion of the LNG 146 can
be removed from LNG 6, expanded in second valve V2, and then warmed
in heat exchanger 40, thereby providing additional refrigeration,
to produce warm natural gas stream 108. The remaining portion can
then be expanded across third valve V3, thereby producing second
portion of the LNG 148. In the embodiment shown in FIG. 3, all of
LNG 6 is expanded in valve V3 and used as product.
[0114] Refrigeration for the system is provided by two sources. The
first refrigeration source can be via a conventional nitrogen
refrigeration cycle 50. Nitrogen gas is compressed in nitrogen
recycle compressor 10, cooled in cooler 11, compressed further in
booster of first turbine booster 20, cooled in cooler 21, then
further compressed in booster of second turbine booster 25 before
being cooled again in cooler 26. The resulting compressed nitrogen
is then cooled in heat exchanger 40, wherein a first portion is
removed and expanded in turbine of second turbine booster 25, a
second portion is removed and expanded in turbine of first turbine
booster 20. The resulting expanded nitrogen streams are then
introduced to heat exchanger 40, where they are warmed via indirect
heat exchange against the natural gas and other nitrogen
streams.
[0115] The second refrigeration source is provided by using the
excess pressure differential of the high pressure natural gas. In
this embodiment, second portion of the natural gas stream 106 is
split from high pressure natural gas 2, and then purified in second
purification unit 131 of at least water and preferably mercury to
produce purified second portion of the natural gas 132. While the
embodiment shown in FIG. 3 includes two separate purification
units, it is possible to use a single purification unit to fully
purify the entire natural gas stream prior to splitting the natural
gas into two streams. However, it is preferable to split the
streams prior to purification since the natural gas used to provide
refrigeration (i.e., the portion not liquefied), does not need to
have carbon dioxide removed, since the natural gas turbine outlet
stream 144 is at a sufficiently warm temperature such that carbon
dioxide will not freeze within this stream. In another embodiment,
units 130 and 131 may be combined into a single unit, and the
moisture free stream (e.g., 132) is removed at an intermediate
location of the vessel and the moisture and CO.sub.2 free stream
(e.g., 104) is removed from the end of the vessel opposite the feed
location.
[0116] Purified second portion of the natural gas 132 can then be
partially cooled in heat exchanger 40, before being expanded in
turbine 121 of natural gas turbine booster 120 to form cold natural
gas stream 144. Alternatively, in an embodiment not shown, purified
second portion of the natural gas stream 132 can be sent, prior to
cooling, directly to natural gas turbine 121 for expansion. This
can help limit the temperature of 144 to avoid heavy hydrocarbon
condensation and potential solidification. Cold natural gas stream
144 is then reintroduced to heat exchanger 40, wherein it is warmed
via indirect heat exchange and collected as warm natural gas stream
108 from the warm end of the heat exchanger. In one embodiment,
cold natural gas stream 144 can be combined with heavy hydrocarbons
8 within the heat exchanger, or the different streams can warm
individually within the heat exchanger and be combined following
their warming.
[0117] The booster 101 of natural gas turbine booster 120 can be
located at many different locations depending on the natural gas
source and return pressures. For example, it may be located at 1)
the NG stream to be expanded (FIG. 2) if the feed pressure and/or
return pressure are low, 2) the total natural gas feed flow before
splitting the flow to be expanded and flow to be liquefied (FIG.
3), or 3) on the discharge of the turbine at the warm end of the
exchanger (e.g., stream 108) in the case of high natural gas feed
pressure and high natural return pressure (not shown), or 4) on
stream to be liquefied (e.g., stream 104) if the feed pressure is
low (not shown). Alternatively the turbine may be used to drive an
electrical generator or dissipated by oil brake (not shown).
[0118] The primary difference between the embodiment of FIG. 2 and
the embodiment of FIG. 3 is that in FIG. 3, low pressure gaseous
nitrogen is introduced as feed into the nitrogen refrigeration
cycle and LIN is coproduced with LNG. In one particular embodiment,
gaseous nitrogen ("GAN") is introduced into, and compressed by,
nitrogen compressor 15 before being cooled in cooler 16 and then
added to the refrigeration cycle. Those of ordinary skill in the
art will recognize that the nitrogen compressor 15 can be optional,
since its use can be dependent on the pressure of the GAN feed
stream. In another embodiment, a third portion of the cooled
nitrogen is removed from the heat exchanger 40, subcooled in
nitrogen subcooler 45, and expanded across valve V4 before being
introduced to nitrogen gas liquid separator 55. Nitrogen vapor 57
is withdrawn from the top of nitrogen gas liquid separator 55 and
then warmed in heat exchanger 40, wherein it is then recompressed
by nitrogen compressor 15 before again rejoining the refrigeration
cycle. Liquid nitrogen is withdrawn from the bottom of nitrogen gas
liquid separator 55 and preferably one portion 51 is sent to be
vaporized in subcooler 45, while the other portion 52 is sent to a
liquid nitrogen storage tank (not shown).
[0119] As such, FIG. 3 provides for an embodiment in combining
LIN+LNG+natural gas letdown. As before, the nitrogen refrigeration
cycle includes a recycle compressor, and at least one turbine
booster. However, because it produces LIN (e.g., removes nitrogen
molecules from the loop), it also includes a step of adding gaseous
nitrogen feed to the system. In the embodiment shown in FIG. 3, the
gaseous nitrogen makeup is at low pressure, and therefore it also
includes a nitrogen feed compressor, as well as a subcooler to
provide liquid nitrogen product. As in other embodiments, the
natural gas supply is split between a flow to be liquefied and a
flow to be expanded back to low pressure. As noted previously, the
natural gas booster 101 may be located at various locations
depending on the flow ratio and pressure of the natural gas feed
and letdown pressures used.
[0120] Regarding FIG. 4, a process flow diagram of an embodiment
having a partial integration of a nitrogen liquefier with a natural
gas liquefier is shown. In FIG. 4, natural gas can be acquired from
a natural gas source, compressed in natural gas booster 101 to
produce high pressure natural gas 2. High pressure natural gas 2 is
preferably split into two portions, with one portion being
liquefied and the other portion providing a portion of the
refrigeration used to liquefy the natural gas. First portion of the
natural gas stream 102 is purified in first purification unit 130,
wherein acid gases, water and mercury are preferably removed.
Preferably, any impurity within the natural gas that would damage
equipment or solidify prior to the natural gas liquefying is
removed in first purification unit 130. The resulting purified
first portion of the natural gas stream 104 is then withdrawn from
first purification unit 130 and introduced to heat exchanger 440
for liquefaction therein. In embodiments in which the natural gas
feed contains heavy hydrocarbons, it is preferable to withdraw
purified first portion of the natural gas 104 from an intermediate
section of heat exchanger 440 or before entering exchanger 440 and
separate the heavy hydrocarbons 8 using gas liquid separator 5 or
distillation column. In one embodiment, heavy hydrocarbons 8 may be
expanded and then warmed in heat exchanger 440. The resulting
warmed stream can be combined with other natural gas streams (e.g.,
cold natural gas stream 144) within heat exchanger 440. This
advantageously captures some of the cold energy from heavy
hydrocarbons 8, and if warm natural gas stream 108 is subsequently
used for fuel, it also provides additional energy for that purpose.
Vaporized natural gas from gas liquid separator 5 is reintroduced
to heat exchanger 440, wherein it subsequently liquefies to produce
LNG 6.
[0121] Refrigeration for the system can be provided by three
sources, a first nitrogen refrigeration cycle 50, a second nitrogen
refrigeration cycle 450, and by expansion of high pressure natural
gas. In first nitrogen refrigeration cycle 50, nitrogen gas coming
from first nitrogen refrigeration cycle 50 and second nitrogen
refrigeration cycle 450 is compressed in shared nitrogen recycle
compressor 410, and cooled in cooler 411. The resulting compressed
nitrogen is then split into two streams, with a first portion going
to first nitrogen refrigeration cycle 50 and the second portion
going to second nitrogen refrigeration cycle 450.
[0122] With respect to first nitrogen refrigeration cycle 50, the
nitrogen can be compressed further in booster of first turbine
booster 20, cooled in cooler 21, further compressed in booster of
second turbine booster 25 before being cooled again in cooler 26.
The resulting compressed nitrogen is then cooled in heat exchanger
40, wherein a first portion is removed and expanded in turbine of
second turbine booster 25, a second portion is removed and expanded
in turbine of first turbine booster 20. The resulting expanded
nitrogen streams are then introduced to heat exchanger 40, where
they are warmed via indirect heat exchange against the natural gas
and other nitrogen streams, and then sent back to shared nitrogen
recycle compressor 410.
[0123] As in FIG. 3, the embodiment of FIG. 4 also includes low
pressure gaseous nitrogen introduced as feed and LIN is coproduced.
Gaseous nitrogen (GAN) is introduced into, and compressed by,
nitrogen compressor 15 before being cooled in cooler 16 and then
added to the refrigeration cycle. Those of ordinary skill in the
art will recognize that the nitrogen compressor 15 can be optional,
since its use can be dependent on the pressure of the GAN feed
stream. Additionally, the remaining portion of the compressed
nitrogen is removed from the heat exchanger 40, subcooled in
nitrogen subcooler 45, and expanded across valve V4 before being
introduced to nitrogen gas liquid separator 55. Nitrogen vapor 57
is withdrawn from the top of nitrogen gas liquid separator 55 and
then warmed in heat exchanger 40, wherein it is then recompressed
by nitrogen compressor 15 before again rejoining the refrigeration
cycle. Liquid nitrogen is withdrawn from the bottom of nitrogen gas
liquid separator 55 then split into first portion 51 which is
vaporized in subcooler 45 to provide heat exchange for the LIN
subcooling and second portion 52 as LIN production preferably sent
to a storage tank (not shown).
[0124] The second refrigeration source can be second nitrogen
refrigeration cycle 450, which is comprised of shared nitrogen
recycle compressor 410, shared cooler 411, and non-shared equipment
such as third turbine booster 420, cooler 421, fourth turbine
booster 425, and cooler 426.
[0125] The third source of refrigeration is provided by using
available excess pressure differential of high pressure natural
gas. In this embodiment, second portion of the natural gas stream
106 is split from high pressure natural gas 2, and then purified in
second purification unit 131 of at least water and preferably
mercury to produce purified second portion of the natural gas 132.
While the embodiment shown in FIG. 4 includes two separate
purification units, it is possible to use a single purification
unit to fully purify the entire natural gas stream prior to
splitting the natural gas into two streams. However, it is
preferable to split the streams prior to purification since the
natural gas used to provide refrigeration (i.e., the portion not
liquefied), does not need to have carbon dioxide removed, since the
natural gas turbine outlet stream 144 is at a sufficiently warm
temperature such that carbon dioxide will not freeze within this
stream. Alternatively, units 130 and 131 may be combined into a
single unit such that the moisture free stream 132 is removed at an
intermediate location of the vessel and the moisture and CO.sub.2
free stream 104 is removed from the end of the vessel opposite the
feed 2 location.
[0126] Purified second portion of the natural gas 132 may be
partially cooled in heat exchanger 440, before being expanded in
natural gas turbine 121 to form cold natural gas stream 144.
Alternatively, stream 132 can be sent, prior to cooling in the heat
exchanger, to turbine 121 for expansion to limit the temperature of
144 due to CO.sub.2 freezing or heavy hydrocarbon condensation.
Cold natural gas stream 144 is then reintroduced to heat exchanger
440, wherein it is warmed via indirect heat exchange and collected
as warm natural gas stream 108 from the warm end of the heat
exchanger. In one embodiment, cold natural gas stream 144 can be
combined with heavy hydrocarbons 8 within the heat exchanger, or
the two streams can warm individually within the heat exchanger and
be combined following their warming.
[0127] The booster 101 of natural gas turbine booster 120 can be
located at many different locations depending on the natural gas
source and return pressures. For example, it may be located at 1)
the NG stream to be expanded (FIG. 2) if the feed pressure and/or
return pressure are low, 2) the total natural gas feed flow before
splitting the flow to be expanded and flow to be liquefied (FIG.
3), or 3) on the discharge of the turbine at the warm end of the
exchanger (e.g., 108) in the case of high natural gas feed pressure
and high natural return pressure (not shown), or 4) on stream to be
liquefied (e.g., 104) if the feed pressure is low (not shown).
Alternatively the turbine may be used to drive an electrical
generator or dissipated by oil brake (not shown).
[0128] As noted above, the embodiment of FIG. 4 preferably includes
a stand-alone nitrogen liquefier 350, that shares a common nitrogen
recycle compressor (e.g., 410), with the second nitrogen
refrigeration cycle 450. As such, such an embodiment can
advantageously produce LIN and LNG at locations that have both a
nitrogen liquefaction unit and access to natural gas.
[0129] The embodiment of FIG. 4 has a 12% efficiency improvement
compared to the embodiment shown in FIG. 3, primarily due to the
additional turbine boosters which can be positioned at temperatures
in the cycle to independently optimize the LNG and LIN trains.
[0130] Additionally, the shared recycle compressor 410 provides a
lower capital cost compared to an independent nitrogen liquefier
plus independent LNG plant, since the embodiment effectively
eliminates one recycle compressor, which typically is the largest
capital cost equipment of the system. In addition, there is a small
efficiency improvement due to a single, large machine compared to
two, small machines. Similarly as indicated before, the location of
the booster for the natural gas letdown can vary with natural gas
source and letdown pressure.
[0131] A comparison of the embodiments shown in FIGS. 1-4 can be
found in Table II below.
TABLE-US-00002 TABLE II Comparison Data for FIGS. 1-4 LNG + LIN
Base (Typical LNG LNG production by production by NG LNG + LIN
production production by N2 NG letdown and N2 letdown and N2 by NG
letdown and N2 cycle) FIG. 1 cycle. FIG. 2 cycle (FIG. 3) cycle
(FIG. 4) NG supply 32 bara 342 1019 1019 1019 (mtd) NG to letdown
5.6 0 677 677 677 bara (mtd) LNG Production 342 342 342 342 (mtd)
N2 cycle power input 7155 4158 10555 9974 (kW) LNG Specific power
502 292 353 313 (kWh/mt) Power Reduction (%) -- 42% 30% 38% LIN
production -- -- 301 301 (mtd) LIN Specific Power -- -- 440 440
(kWh/mt)
[0132] In an optional embodiment, fourth gas stream 351 can be
cooled and/or liquefied within heat exchanger 40 to produce
cooled/liquefied fourth gas stream 352. In one embodiment, fourth
gas stream 351 is selected from the group consisting of natural
gas; ethane; ethylene; acetylene; C.sub.3-C.sub.6 alkanes, alkenes
and alkynes; nitrogen; hydrogen; and helium. In embodiments in
which gas stream 351 is hydrogen or helium, gas stream 352 is
preferably not liquefied. Otherwise, cooled stream 352 is
preferably liquefied. Advantageously, this optional embodiment
allows for three separate gases to be liquefied (e.g., streams 52,
352 and 6).
[0133] The embodiments shown in FIG. 3 and FIG. 4 are preferably
located near, on, or have access to an industrial site with a large
constant letdown flow of natural gas (e.g., a cogen unit, or steam
methane reformer facility), as well as a source of nitrogen (e.g.,
near an air separation unit "ASU" or nitrogen pipeline). Nitrogen
is often available near an ASU as they are commonly designed for
O.sub.2 production. Nitrogen may be extracted with a small cost to
the ASUs precooling system.
[0134] The embodiment shown in FIG. 4 includes a specific
embodiment of producing LNG and LIN, however, the invention is not
to be so limited. Instead, an embodiment of the invention can
include liquefaction of a first gas and a second gas, through the
use of two refrigeration cycles, in which the two refrigeration
cycles share a common recycle compressor. In a preferred
embodiment, the refrigeration cycles are nitrogen refrigeration
cycles. In one embodiment, the two liquefiers could each produce
either LIN or LNG or liquid hydrogen or liquid helium or any type
of other industrial gases. In another embodiment, either or both of
the liquefiers may have an expansion device configured to expand a
higher pressure gas source.
[0135] Embodiments of the invention can have wide applications in
the industry. For example, an embodiment of the invention may
include identifying an underutilized liquefaction system, and then
adding a second liquefier nearby (e.g., an LNG liquefier). The
original liquefier can be slightly modified in order to allow for
its previously underutilized recycle compressor to provide
compression for both refrigeration cycles. This allows for the new
liquefier to produce its liquid in a much more efficient manner. In
another embodiment, the second liquefaction unit is preferably
located nearby a high and low pressure pipeline network (e.g.,
natural gas pipeline) such that the system is able to use the
refrigeration from expansion of the natural gas.
[0136] In another embodiment, two new liquefiers can be built to
satisfy a market demand. For example, the first liquefier can be a
nitrogen liquefaction unit and the second liquefier can be a
natural gas liquefaction unit, both using nitrogen refrigeration
cycles. It can be economically advantageous that at least one of
the liquefiers is a standardized plant (e.g., a modular type design
that can be designed and produced in bulk). In many cases, the
capacity which the standardized plant has been designed for is
greater than the capacity needed for this specific application. A
similar concept could apply to the relocation of an existing
liquefier. Therefore, the second liquefier can be built such that
its refrigeration cycle uses the same recycle compressor as the one
from the first liquefier. It is also common that such liquefaction
plants are located near an industrial area, therefore benefiting
from a wide natural gas pipeline network. One or both liquefiers
would benefit from adding a natural gas expansion refrigeration to
each nitrogen refrigeration cycle, as described herein.
[0137] Similarly, if the standardized plant were undersized for a
particular application (e.g., produce liquid nitrogen), the second
liquefaction unit could be designed to make up the difference. In
this embodiment, the second liquefaction unit could be configured
to create both a liquid nitrogen product, as well as an LNG
product.
[0138] Operational problems can occur when the natural gas turbine
drives an electric generator without extracting the refrigeration
energy of expansion. Furthermore, in some instances, the flow rate
and pressures of the natural gas can often fluctuate. This can
cause issues with respect to fluctuations in produced energy, since
electrical systems are not always able to accept the resulting
fluctuations of electricity sent to the grid from the generator.
Similarly, the resulting fluctuations in cold created by the
natural gas expansion can yield fluctuations in other
utilities.
[0139] In certain embodiments of the invention, the above
referenced problems can be mitigated through the use of an LNG
and/or LIN storage tank, as the storage tank provides a buffer for
the fluctuations of the refrigeration balance. For example, minor
fluctuations in natural gas conditions can be accounted for by
adjusting the load of the nitrogen refrigeration cycle and the
quantity of LNG and/or LIN being liquefied. Large or long term
fluctuations can be accounted for by stopping the liquefier and
compensating by the tank level. In addition, significant short term
fluctuations can be accounted for by adjusting a bypass valve to
allow high pressure natural gas to bypass the liquefier and going
straight to the MP GAN stream (not shown). In another embodiment,
the method can include monitoring various process conditions (e.g.,
pressure, flow rate, gas composition, etc. . . . ) of the natural
gas source, and/or streams downstream of the natural gas source.
Based on these monitored process conditions, various set points can
be adjusted in order to further optimize the system. For example, a
set point that can be adjusted can include expansion ratio for the
various turbines, along with flow rates of various streams
throughout. In one embodiment, the set points for the flow rate and
inlet pressure to the natural gas turbine can be controlled within
an acceptable operating range of the liquefaction equipment by
adjustment of the natural gas bypass valve and/or a turbine inlet
control valve. In one embodiment, the method can include a central
process controller that is configured to receive the various
monitored process conditions and then determine whether a selected
set point should be adjusted based on the monitored process
conditions. The monitoring devices can communicate with the
controller via all known methods, for example, both wirelessly and
via wired electrical communication.
[0140] FIG. 5 provides for a process flow diagram with liquid
nitrogen production being supplemented with refrigeration from
letdown of natural gas. The additional energy provided by the
natural gas letdown reduces the power and size of the nitrogen
refrigeration cycle for a fixed LIN production depending on the
amount of energy which can be removed from the natural gas letdown
(i.e., flow and pressure ratio of the NG letdown).
[0141] In this type of embodiment, it is preferable that the system
be proximate to a nitrogen source (e.g., ASU with available
nitrogen production, or other small dedicated nitrogen generator,
or nitrogen pipeline) as well as a source of pressurized natural
gas suitable for letdown. While it is understood that there will be
variations in the natural gas flow and pressure, the liquefier can
accommodate some of these variations by a corresponding adjustment
in LIN production and or power from the nitrogen refrigeration
cycle.
[0142] The method shown in FIG. 5 has one natural gas turbine
booster for the warm section of the exchanger and one nitrogen
turbine booster for the cold section. However, for improved
efficiency and flexibility, an additional warm turbine booster (as
shown in FIG. 2) can be included in certain embodiments of the
invention.
[0143] With respect to purification, water should be removed and
depending on natural gas composition, pressure and temperature
prior to natural gas expansion, acid gases such as CO.sub.2, and
other impurities which freeze at colder temperatures may be removed
from the natural gas as well. The natural gas may be cooled before
being expanded and can reach a temperature of approximately
-60.degree. C. to -100.degree. C. before entering the heat
exchanger, is re-warmed and returned to the low pressure header.
Since CO.sub.2 will only freeze at lower temperatures, it is not
required to remove CO.sub.2 from the stream being expanded.
[0144] Since the liquefier is intended to be in industrial
facilities with constant natural gas letdown, nitrogen source, etc,
these facilities often have much less impurities in the feed
natural gas. For example odorization (addition of sulfur containing
mercaptans) is not used in these areas. Therefore, the purification
system maybe simplified compared to a similar unit installed at a
non-industrial site.
[0145] Those of ordinary skill in the art will recognize that other
types of refrigeration cycles may be used. Therefore, embodiments
of the invention are not intended to be limited to the particular
refrigeration cycles shown and described within the detailed
specification and in the accompanying figures. Additionally, while
the embodiments shown in the figures and discussed herein,
typically show that the natural gas expansion turbine can be
connected to a natural gas booster, certain embodiments of the
invention are not intended to be so limited. Rather, in certain
embodiments of the invention, the natural gas expansion turbine 121
can drive a booster that is located within one of the refrigeration
cycles, for example the nitrogen refrigeration cycle. In this
embodiment, the booster can be configured to compress a
refrigeration fluid (for example, nitrogen) within the
refrigeration cycle.
[0146] While the invention has been described in conjunction with
specific embodiments thereof, it is evident that many alternatives,
modifications, and variations will be apparent to those skilled in
the art in light of the foregoing description. Accordingly, it is
intended to embrace all such alternatives, modifications, and
variations as fall within the spirit and broad scope of the
appended claims. The present invention may suitably comprise,
consist or consist essentially of the elements disclosed and may be
practiced in the absence of an element not disclosed. Furthermore,
if there is language referring to order, such as first and second,
it should be understood in an exemplary sense and not in a limiting
sense. For example, it can be recognized by those skilled in the
art that certain steps can be combined into a single step.
[0147] The singular forms "a", "an" and "the" include plural
referents, unless the context clearly dictates otherwise.
[0148] "Comprising" in a claim is an open transitional term which
means the subsequently identified claim elements are a nonexclusive
listing (i.e., anything else may be additionally included and
remain within the scope of "comprising"). "Comprising" as used
herein may be replaced by the more limited transitional terms
"consisting essentially of" and "consisting of" unless otherwise
indicated herein.
[0149] "Providing" in a claim is defined to mean furnishing,
supplying, making available, or preparing something. The step may
be performed by any actor in the absence of express language in the
claim to the contrary.
[0150] Optional or optionally means that the subsequently described
event or circumstances may or may not occur. The description
includes instances where the event or circumstance occurs and
instances where it does not occur.
[0151] Ranges may be expressed herein as from about one particular
value, and/or to about another particular value. When such a range
is expressed, it is to be understood that another embodiment is
from the one particular value and/or to the other particular value,
along with all combinations within said range.
[0152] All references identified herein are each hereby
incorporated by reference into this application in their
entireties, as well as for the specific information for which each
is cited.
* * * * *