U.S. patent application number 13/799036 was filed with the patent office on 2014-09-18 for combined heat and power technology for natural gas liquefaction plants.
The applicant listed for this patent is Apache Corporation. Invention is credited to Devendra Agrawal, John Ray, Bret Shapot, Eric Southward.
Application Number | 20140260251 13/799036 |
Document ID | / |
Family ID | 50555256 |
Filed Date | 2014-09-18 |
United States Patent
Application |
20140260251 |
Kind Code |
A1 |
Shapot; Bret ; et
al. |
September 18, 2014 |
Combined Heat and Power Technology for Natural Gas Liquefaction
Plants
Abstract
Systems and methods for the generation of liquid natural gas
("LNG") are provided.
Inventors: |
Shapot; Bret; (Houston,
TX) ; Agrawal; Devendra; (Sugar Land, TX) ;
Ray; John; (Katy, TX) ; Southward; Eric;
(Katy, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Apache Corporation |
Houston |
TX |
US |
|
|
Family ID: |
50555256 |
Appl. No.: |
13/799036 |
Filed: |
March 13, 2013 |
Current U.S.
Class: |
60/648 ;
60/655 |
Current CPC
Class: |
Y02E 20/14 20130101;
Y02P 80/15 20151101; F25J 2220/68 20130101; F25J 1/0242 20130101;
F25J 2205/66 20130101; Y02P 80/154 20151101; F01K 17/025 20130101;
F25J 2240/82 20130101; F01K 23/06 20130101; F25J 1/0287 20130101;
F25J 2240/70 20130101; F25J 1/029 20130101; F01K 23/10 20130101;
F25J 2245/90 20130101; F25J 1/0022 20130101; F25J 2220/64 20130101;
F25J 1/0283 20130101; F01K 3/24 20130101; F01K 23/064 20130101 |
Class at
Publication: |
60/648 ;
60/655 |
International
Class: |
F01K 23/06 20060101
F01K023/06 |
Claims
1. A system for the generation of liquefied natural gas comprising:
a) a first gas turbine; b) a first steam generator in gaseous
communication with the first gas turbine; c) a second gas turbine;
d) a second steam generator in gaseous communication with the
second gas turbine; e) a steam turbine in gaseous communication
with the first steam generator and the second steam generator; and
f) an electrical generator in mechanical communication with the
steam turbine.
2. The system of claim 1, further comprising a first helper motor
and a second helper motor electrically connected to the
generator.
3. The system of claim 2, wherein the first helper motor is
mechanically connected to the first gas turbine and the second
helper motor is mechanically connected to the second gas
turbine.
4. The system of claim 2, wherein the first helper motor and the
second helper motor are synchronous or induction motors.
5. The system of claim 4, wherein the synchronous or induction
motors are connected to voltage source inverter drives.
6. The system of claim 1, further comprising a first shaft attached
to the first gas turbine and a second shaft attached to the second
gas turbine.
7. The system of claim 6, further comprising at least a first
refrigeration compressor attached to the first shaft and at least a
second refrigeration compressor attached to the second shaft.
8. The system of claim 7, further comprising at least a first
cooler in liquid communication with the at least a first
refrigeration compressor and at least a second cooler in liquid
communication with the at least a second refrigeration
compressor.
9. The system of claim 8, further comprising a scrub column in
gaseous communication with the plurality of coolers.
10. The system of claim 9, further comprising a cryogenic heat
exchanger in gaseous communication with the scrub column.
11. The system of claim 10, further comprising a liquefied natural
gas storage tank in liquid communication with the cryogenic heat
exchanger.
12. The system of claim 11, further comprising a boil off gas
compressor in gaseous communication with the liquefied natural gas
storage tank.
13. The system of claim 12, further comprising a boil off gas
compressor motor connected to the boil off gas compressor and
electrically connected to the generator.
14. The system of claim 13, wherein the boil off gas compressor
motor is a high speed synchronous or induction motor.
15. The system of claim 14, wherein the high speed motor is
connected to a variable frequency drive.
16. A waste heat recovery system, comprising: a) a first gas
turbine; b) a first steam generator in gaseous communication with
the first gas turbine; c) a second gas turbine; d) a second steam
generator in gaseous communication with the second gas turbine; e)
a steam turbine in gaseous communication with the first steam
generator and the second steam generator; and f) an electrical
generator in mechanical communication with the steam turbine.
17. A method for the reduction of fuel gas consumption during the
production of liquefied natural gas in a liquefied natural gas
facility comprising a first gas turbine that generates a first
amount of waste heat upon operation and a second gas turbine that
generates a second amount of waste heat upon operation, comprising:
a) utilizing the first amount of waste heat from the first gas
turbine in a first heat recovery steam generator to produce a first
amount of steam; b) utilizing the second amount of waste heat from
the second gas turbine in a second heat recovery steam generator to
produce a second amount of steam; c) utilizing at least a portion
of the first amount of steam and the second amount of steam in a
steam turbine; d) producing electricity from a generator connected
to the steam turbine; and e) utilizing the electricity to power at
least a first process that consumes electrical power generated from
fuel gas used during the production of liquefied natural gas in a
liquefied natural gas facility, thereby reducing fuel gas
consumption.
18. The method of claim 17, wherein the at least a first process
that consumes electrical power generated from fuel gas is operation
of a first helper motor.
19. The method of claim 17, wherein the at least a first process
that consumes electrical power generated from fuel gas is operation
of a boil off gas compressor motor.
20. The method of claim 17, wherein the at least a first process
that consumes fuel gas is production of electricity used in the
liquefied natural gas facility.
21. The method of claim 17, comprising utilizing the electricity to
power at least a first and at least a second process that consume
fuel gas used during the production of liquefied natural gas in a
liquefied natural gas facility.
22. The method of claim 21, wherein the at least a first process
that consumes fuel gas is operation of a first helper motor and the
at least a second process that consumes fuel gas is operation of a
second helper motor.
23. A method for the reduction of greenhouse gas emissions during
the production of liquefied natural gas in a liquefied natural gas
facility comprising a first gas turbine that generates a first
amount of waste heat upon operation and a second gas turbine that
generates a second amount of waste heat upon operation, comprising:
a) utilizing the first amount of waste heat from the first gas
turbine in a first heat recovery steam generator to produce a first
amount of steam; b) utilizing the second amount of waste heat from
the second gas turbine in a second heat recovery steam generator to
produce a second amount of steam; c) utilizing at least a portion
of the first amount of steam and the second amount of steam in a
steam turbine; d) producing electricity from a generator connected
to the steam turbine; and e) utilizing the electricity to power at
least a first process that generates greenhouse gas emissions used
during the production of liquefied natural gas in a liquefied
natural gas facility, thereby reducing greenhouse gas
emissions.
24. A plant for the generation of liquefied natural gas comprising:
a) an inlet gas reception unit connected to a natural gas pipeline;
b) a gas treating and dehydration unit in gaseous communication
with the inlet gas reception unit; c) a liquefaction unit in
gaseous communication with the gas treating and dehydration unit;
d) a storage and loading unit in liquid communication with the
liquefaction unit; and e) a waste heat recovery system in
communication with the liquefaction unit, comprising: i) a first
steam generator; ii) a second steam generator; iii) a steam turbine
in gaseous communication with the first steam generator and the
second steam generator; and iv) an electrical generator connected
to the steam turbine.
25. A plant for the generation of liquefied natural gas comprising:
a) a pig receiver connected to a natural gas pipeline; b) a filter
coalescer in gaseous communication with the pig receiver; c) a
meter in gaseous communication with the filter coalescer; d) an
acid gas absorber in gaseous communication with the meter; e) a
drier precooler in gaseous communication with the acid gas
absorber; f) a drier inlet separator in gaseous communication with
the drier precooler; g) a plurality of gas driers in gaseous
communication with the drier inlet separator; h) a first gas
turbine in gaseous communication with the plurality of gas driers;
i) a first plurality of refrigeration compressors connected to the
first gas turbine; j) a second gas turbine in gaseous communication
with the plurality of gas driers; k) a second plurality of
refrigeration compressors connected to the second gas turbine; l) a
mercury adsorber in gaseous communication with the plurality of gas
driers; m) a filter in gaseous communication with the mercury
adsorber; n) a plurality of coolers in gaseous communication with
the filter; o) a scrub column in gaseous communication with the
plurality of coolers; p) a cryogenic heat exchanger in gaseous
communication with the scrub column; q) a LNG storage tank in fluid
communication with the cryogenic heat exchanger; r) a boil off gas
compressor in gaseous communication with the LNG storage tank; s) a
high speed motor connected to the boil off gas compressor; t) a
variable frequency drive connected to the high speed motor; and u)
a waste heat recovery system, comprising: i) a first steam
generator in gaseous communication with the first gas turbine; ii)
a second steam generator in gaseous communication with the second
gas turbine; iii) a steam turbine in gaseous communication with the
first steam generator and the second steam generator; and iv) an
electrical generator connected to the steam turbine.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not Applicable
THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT
[0003] Not Applicable
INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT
DISC
[0004] Not Applicable
BACKGROUND OF THE INVENTION
[0005] 1. Field of the Invention
[0006] This invention relates generally to systems and methods for
the generation of liquefied natural gas ("LNG").
[0007] 2. Description of the Related Art
[0008] Natural gas can be converted to liquefied natural gas
("LNG") by cooling it to about -161.degree. C., depending on the
exact composition of the natural gas, which reduces its volume to
about 1/600th of its original value. This reduction in volume can
make transportation more economical. For example, the LNG can be
transferred to a cryogenic storage tank located on an ocean-going
ship. Once the ship arrives at its destination, the LNG can be
offloaded to a regasification facility, in which it is converted
back into gas by heating it. Once the LNG has been regasified, the
natural gas can be transported by pipeline or other means to a
location where the natural gas can be used as a fuel or a raw
material for manufacturing other chemicals.
[0009] The conventional process for LNG production involves gas
turbine driven refrigeration compressors. The exhaust flue gas from
the gas turbines is typically discharged to the atmosphere.
Additional compression power is typically supplied through use of
gas turbine generators or other external sources, with the help of
large synchronous motors with load commutated inverter ("LCI")
drives, which require additional fuel gas consumption leading to
higher operating costs and higher plant greenhouse gas emissions.
Synchronous motors are larger, more expensive, less reliable and
require more control equipment than induction motors, but large
induction motors that can operate at high speeds are not known in
the art.
[0010] What is needed therefore are systems and methods to reduce
fuel gas consumption and greenhouse gas emissions in LNG
facilities.
SUMMARY OF THE INVENTION
[0011] The present disclosure overcomes one or more of the
deficiencies of the prior art by providing systems and methods to
recover and utilize waste heat generated in LNG facilities, thereby
reducing fuel gas consumption and reducing greenhouse gas
emissions. In the present disclosure power to supply all of the LNG
plant's electrical demand can be extracted from gas turbine waste
heat. The power can be generated in a dedicated onsite power unit
that is located to optimize the layout of the overall production
facility. The separation of the power facility from the
liquefaction area allows for more efficient operation of the power
unit and utilization of plot space as the equipment used requires
significant space that is not generally available in the
liquefaction area.
[0012] Another feature of the present disclosure is that the steam
produced from waste heat can also be utilized for process heating,
thus further reducing the demand for fuel. Heating steam may be
taken directly from the steam generators for operations that
require higher heating temperatures. For lower temperature heating
requirements steam may be extracted at lower pressures from the
steam turbine, allowing high value mechanical power to be extracted
from the steam to generate electrical power before the steam is
supplied to the process heating operations. The low pressure steam
extracted from the turbine has the further benefit of reducing the
load on the air cooled steam condensers.
[0013] An additional and optional feature of the present disclosure
is that hydrocarbon waste liquid streams may be burned in the gas
turbine exhaust duct to provide supplemental energy needs of the
process and to simultaneously eliminate a stream that is otherwise
difficult to dispose of economically. Natural gas or other
supplemental gas fuel may also be burned if additional energy is
required for power production and/or heating services. For
flexibility, sparing, and to facilitate plant startups, a separate
standalone boiler may also be provided.
[0014] The present disclosure provides a system for the generation
of liquefied natural gas comprising a first gas turbine, a first
steam generator in gaseous communication with the first gas
turbine, a second gas turbine, a second steam generator in gaseous
communication with the second gas turbine, a steam turbine in
gaseous communication with the first steam generator and the second
steam generator, and an electrical generator in mechanical
communication with the steam turbine. Gas turbines are routinely
used in the production of liquefied natural gas, and the present
disclosure provides an improved system and process for the
production of liquefied natural gas using gas turbines, the
improvement comprising a waste heat recovery system comprising a
first steam generator in gaseous communication with a first gas
turbine, a second steam generator in gaseous communication with a
second gas turbine, a steam turbine in gaseous communication with
the first steam generator and the second steam generator, and an
electrical generator in mechanical communication with the steam
turbine. Thus the present disclosure provides for the utilization
of the heat generated by the gas turbines used in the production of
liquefied natural gas, which previously was wasted, to produce
electricity. In certain embodiments enough electricity is produced
from the heat generated by the gas turbines to power the entire
natural gas production facility.
[0015] In additional embodiments the system further comprises a
first helper motor and a second helper motor electrically connected
to the electrical generator. In further embodiments the first
helper motor is mechanically connected to the first gas turbine and
the second helper motor is mechanically connected to the second gas
turbine. In general the first helper motor and the second helper
motor are synchronous or induction motors, although other types of
motors can find uses in certain embodiments. The synchronous or
induction motors can be connected to voltage source inverter
drives, although other types of drives can be connected to the
motors in particular embodiments.
[0016] The disclosed system can further comprise a first drive
shaft attached to the first gas turbine and a second drive shaft
attached to the second gas turbine. The disclosed system can
further comprise at least a first refrigeration compressor
connected or attached to the first drive shaft and at least a
second refrigeration compressor connected or attached to the second
shaft. In additional embodiments the disclosed system comprises at
least a third refrigeration compressor connected or attached to the
first drive shaft. In certain embodiments the system further
comprises at least a first cooler or a plurality of coolers in
liquid communication with the at least a first refrigeration
compressor and at least a second cooler or a plurality of coolers
in liquid communication with the at least a second refrigeration
compressor. The system can further comprise a scrub column in
gaseous communication with the coolers. Furthermore, the system can
comprise a cryogenic heat exchanger in gaseous communication with
the scrub column. As the natural gas has been liquefied at this
point in the process, the system can also include a liquefied
natural gas storage tank in liquid communication with the cryogenic
heat exchanger.
[0017] A certain portion of the stored liquefied natural gas will
boil off. Therefore, in certain embodiments the system further
comprises a boil off gas compressor in gaseous communication with
the liquefied natural gas storage tank. In other embodiments the
system can comprise a boil off gas compressor motor connected to
the boil off gas compressor and electrically connected to the
generator. The boil off gas compressor motor is generally a high
speed synchronous or induction motor, although other types of
motors can find utility in certain aspects of the disclosure. The
high speed synchronous or induction motor can be connected to a
variable frequency drive, although other types of drives can be
used in certain applications.
[0018] The present disclosure also provides a waste heat recovery
system, comprising a first gas turbine, a first steam generator in
gaseous communication with the first gas turbine, a second gas
turbine, a second steam generator in gaseous communication with the
second gas turbine, a steam turbine in gaseous communication with
the first steam generator and the second steam generator, and an
electrical generator in mechanical communication with the steam
turbine.
[0019] The present disclosure additionally provides a method for
the reduction of fuel gas consumption during the production of
liquefied natural gas in a liquefied natural gas facility
comprising a first gas turbine that generates a first amount of
waste heat upon operation and a second gas turbine that generates a
second amount of waste heat upon operation, comprising utilizing
the first amount of waste heat from the first gas turbine in a
first heat recovery steam generator to produce a first amount of
steam, utilizing the second amount of waste heat from the second
gas turbine in a second heat recovery steam generator to produce a
second amount of steam, utilizing at least a portion of the first
amount of steam and the second amount of steam in a steam turbine,
producing electricity from a generator connected to the steam
turbine, and utilizing the electricity to power at least a first
process that consumes electrical power generated from fuel gas used
during the production of liquefied natural gas in a liquefied
natural gas facility, thereby reducing fuel gas consumption. The at
least a first process that consumes electrical power generated from
fuel gas includes, but is not limited to, operation of a first
helper motor, operation of a second helper motor, operation of a
boil off gas compressor motor or production of electricity used in
the liquefied natural gas facility.
[0020] The present disclosure further provides a method for the
reduction of greenhouse gas emissions during the production of
liquefied natural gas in a liquefied natural gas facility
comprising a first gas turbine that generates a first amount of
waste heat upon operation and a second gas turbine that generates a
second amount of waste heat upon operation, comprising utilizing
the first amount of waste heat from the first gas turbine in a
first heat recovery steam generator to produce a first amount of
steam, utilizing the second amount of waste heat from the second
gas turbine in a second heat recovery steam generator to produce a
second amount of steam, utilizing at least a portion of the first
amount of steam and the second amount of steam in a steam turbine,
producing electricity from a generator connected to the steam
turbine, and utilizing the electricity to power at least a first
process that generates greenhouse gas emissions used during the
production of liquefied natural gas in a liquefied natural gas
facility, thereby reducing greenhouse gas emissions.
[0021] Additionally, the present disclosure provides a plant for
the generation of liquefied natural gas comprising, an inlet gas
reception unit connected to a natural gas pipeline, a gas treating
and dehydration unit in gaseous communication with the inlet gas
reception unit, a liquefaction unit in gaseous communication with
the gas treating and dehydration unit, a storage and loading unit
in liquid communication with the liquefaction unit, and a waste
heat recovery system in communication with the liquefaction unit,
comprising a first steam generator, a second steam generator, a
steam turbine in gaseous communication with the first steam
generator and the second steam generator, and an electrical
generator connected to the steam turbine.
[0022] The present disclosure also provides a plant for the
generation of liquefied natural gas comprising a pig receiver
connected to a natural gas pipeline, a filter coalescer in gaseous
communication with the pig receiver, a meter in gaseous
communication with the filter coalesce, an acid gas absorber in
gaseous communication with the meter, a drier precooler in gaseous
communication with the acid gas absorber, a drier inlet separator
in gaseous communication with the drier precooler, a plurality of
gas driers in gaseous communication with the drier inlet separator,
a first gas turbine in gaseous communication with the plurality of
gas driers, a first plurality of refrigeration compressors
connected to the first gas turbine, a second gas turbine in gaseous
communication with the plurality of gas driers, a second plurality
of refrigeration compressors connected to the second gas turbine, a
mercury adsorber in gaseous communication with the plurality of gas
driers, a filter in gaseous communication with the mercury
adsorber, a plurality of coolers in gaseous communication with the
filter, a scrub column in gaseous communication with the plurality
of coolers, a cryogenic heat exchanger in gaseous communication
with the scrub column, a LNG storage tank in fluid communication
with the cryogenic heat exchanger, a boil off gas compressor in
gaseous communication with the LNG storage tank, a high speed motor
connected to the boil off gas compressor, a variable frequency
drive connected to the high speed motor, and a waste heat recovery
system, comprising a first steam generator in gaseous communication
with the first gas turbine, a second steam generator in gaseous
communication with the second gas turbine, a steam turbine in
gaseous communication with the first steam generator and the second
steam generator, and an electrical generator connected to the steam
turbine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The following drawings form part of the present
specification and are included to further demonstrate certain
aspects of the present invention. The invention may be better
understood by reference to one or more of these drawings in
combination with the detailed description of specific embodiments
presented herein.
[0024] FIG. 1. Schematic of a waste heat recovery system.
[0025] FIG. 2. Schematic of LNG facility.
DETAILED DESCRIPTION
[0026] FIG. 1 is a schematic drawing of a LNG facility waste heat
recovery system 100 in accordance with one embodiment of the
present invention. Waste heat recovery system 100 comprises a first
gas turbine 101 connected to a first plurality of refrigeration
compressors 111, although in other embodiments (not shown) the
first gas turbine 101 can be connected to a single refrigeration
compressor 111. In general refrigeration compressors 111 are rotary
type, either centrifugal or axial, although other types and
configurations can find utility in further aspects of the present
disclosure. The first gas turbine 101 produces hot exhaust gas that
travels through a first exhaust line 102 to a first heat recovery
steam generator ("HRSG") 103, which takes boiler feed water from
first water line 104 and produces steam that travels through first
steam line 105. The HRSG 103 may be installed vertically or
horizontally, and may produce steam at one or more pressure levels.
The heat recovery device could also use heating fluids other than
steam, such as organic fluids (not shown). First exhaust line 102
generally comprises a duct burner (not shown), which can use waste
liquid or gas from line 130 and/or supplemental fuel gas from line
132 to produce additional heat for the HRSG 103. Waste heat
recovery system 100 also comprises a second gas turbine 112
connected to a refrigeration compressor 118, although in other
embodiments (not shown) the second gas turbine 112 can be connected
to a plurality of refrigeration compressors 118. The refrigeration
compressors 111 and 118 take low pressure refrigerant streams 138,
139, and 141 and compress them into high pressure refrigerant
streams 137, 140, and 142. The second gas turbine 112 produces hot
exhaust gas that travels through second exhaust line 113 (which can
also comprise a duct burner, not shown) to a second heat recovery
steam generator 114, which takes boiler feed water from second
water line 115 and produces steam that travels through second steam
line 116. Second steam line 116 joins first steam line 105 to form
third steam line 121, which splits into fourth steam line 122 and
fifth steam line 123. Fourth steam line 122 directs steam to higher
temperature process heating tasks 106, for example heating of the
gas used to regenerate natural gas feed dehydrators. Low pressure
steam is extracted from the steam turbine into low pressure steam
line 128 and supplies heat to the lower temperature process heating
tasks 129, which can include, but are not limited to, natural gas
feed heating, and other lower temperature heating demands.
Condensate from the process heating tasks 106 and 129 travels
through first condensate line 124. Fifth steam line 123 directs
steam to steam turbine 107, and wet steam from the steam turbine
107 travels through second condensate line 125 to condenser 143.
Condensate from condenser 143 flows through line 144, which joins
first condensate line 124 to form fourth condensate line 126, which
takes the condensate to a water treatment facility 127. The water
is treated to remove dissolved solids and de-aerated to remove
oxygen and carbon dioxide. Dissolved solids are also prevented from
building up in the water by blowing down a small portion of the
water. The blowdown is replaced by makeup water, which is also
treated for solids removal and de-aerated. Steam turbine 107 is
connected to synchronous generator 108, which generates electricity
for a number of different uses in the LNG facility. Electricity
passes through power line 109 to power helper motor 110 and helper
motor 117, which can each be large induction motors, for example a
25 MW induction motor with voltage source inverter drive that runs
at high speeds (e.g., 3600 RPM), provide utility power 119 and
power for the buildings and lighting 120, as well as through power
line 1011 to power the synchronous or induction electric motor (not
shown in FIG. 1; see FIG. 2) that powers the boil-off gas
compressor (not shown in FIG. 1; see FIG. 2). Induction motors are
more robust (fewer parts which decreases failure rate), up to 30%
less expensive, more reliable, smaller and require less control
equipment than standard synchronous motors with a load commutated
inverter drive, although synchronous motors can be used in certain
embodiments. Although not shown in FIG. 1, the steam from the first
and second heat recovery steam generators can be directed to a
plurality of steam turbines. Fuel for gas turbines 101 and 112 is
boil-off gas from line 136. Also shown in FIG. 1 is a conventional
start-up boiler 133, which uses fuel gas from line 134 to heat
water from water line 135 to produce steam. The steam travels
through line 145 and 105 to the steam generator 107, to produce
electricity needed for start-up operations.
[0027] FIG. 2 is a schematic drawing of a LNG facility 1000
comprising the waste heat recovery system (not shown in FIG. 2; see
FIG. 1). A natural gas enters LNG facility 1000 from pipeline 1001
and passes through inlet gas reception 1012, which can include, but
is not limited to, such components as a meter (not shown) and a
filter coalesce (not shown), through line 1002 to gas treating and
dehydration 1013. In addition to dehydration, gas treating can
include, but is not limited to, such components as an acid gas
absorber (not shown; can be packed or trayed) and a mercury
adsorber (not shown; generally sulfur impregnated carbon that
reacts chemically with the mercury). Line 1003 conveys treated and
dehydrated gas to liquefaction unit 1014, and LNG exits through
line 1004 to storage and loading unit 1015, from which LNG is
loaded for shipping through line 1005. Liquefaction unit 1014
contains the refrigeration compressors 111 and 118 (shown in FIG.
1), with low pressure refrigerant streams 138, 139, and 141 being
compressed by compressors 111 and 118 (see FIG. 1) into high
pressure refrigerant streams 137, 140, and 142. High pressure
refrigerant streams 137, 140 and 142 feed into evaporators (not
shown), which can include propane, propylene, Freon.RTM., ammonia,
or a mixed refrigerant, in the liquefaction unit 1014 generating
low pressure refrigerant streams that feed back into the
refrigeration compressors 111 and 118 (see FIG. 1). The
liquefaction unit 1014 can also comprise a scrub column (not shown)
and/or a cryogenic heat exchanger ("CHE", not shown; but typically
a spiral wound exchanger or series of such exchangers). The
liquefaction unit 1014 could also be a series of brazed aluminum
exchangers and separators located inside a cryogenically insulated
cold box (not shown). Although not shown, reflux for a scrub column
to remove heavy components that could freeze and plug equipment at
cryogenic temperatures can be provided by a partial condensing coil
inside the CHE. Liquefaction unit 1014 can also comprise a liquid
expander (not shown), that removes energy from the LNG, which
improves the overall efficiency while driving a generator (not
shown) to produce additional electricity. A portion of the stored
LNG boils off, and the boil-off gas from storage unit 1015 travels
through line 1006 to a boil-off gas compressor 1007, which is
powered by high speed synchronous or induction electric motor 1008
using electricity from power line 1011 (see also FIG. 1). The speed
of the boil-off gas compressor motor is adjusted by a variable
speed drive (not shown) to match the flow and pressure requirements
of boil-off gas users. Boil-off gas is routed through line 1009 and
split into lines 1010 and 131. Line 1010 flows to gas treating and
dehydration 1013 where it is used for regenerating the gas
dehydrators, and then flows out through line 136 to be used as fuel
in gas turbines 101 and 112. Line 131 conveys boil-off gas not used
for fuel back to liquefaction unit 1014 to be re-liquefied.
[0028] While the present invention has been shown and described in
various embodiments, those skilled in the art will appreciate from
the drawings and the foregoing discussion that various changes,
modifications, and variations may be made without departing from
the spirit and scope of the invention as set forth in the claims.
Hence the embodiments shown and described in the drawings and the
above discussion are merely illustrative and do not limit the scope
of the invention as defined in the claims herein. The embodiments
and specific forms, materials, and the like are merely illustrative
and do not limit the scope of the invention or the claims
herein.
* * * * *