U.S. patent application number 14/808620 was filed with the patent office on 2015-11-19 for systems and methods for natural gas liquefaction capacity augmentation.
The applicant listed for this patent is Bechtel Hydrocarbon Technology Solutions, Inc.. Invention is credited to Sudhir Golikeri, Guang-Chung Lee.
Application Number | 20150330705 14/808620 |
Document ID | / |
Family ID | 52105509 |
Filed Date | 2015-11-19 |
United States Patent
Application |
20150330705 |
Kind Code |
A1 |
Lee; Guang-Chung ; et
al. |
November 19, 2015 |
Systems and Methods for Natural Gas Liquefaction Capacity
Augmentation
Abstract
Systems and methods for natural gas liquefaction capacity
augmentation using supplemental cooling systems and methods to
improve the efficiency of a liquefaction cycle for producing
liquefied natural gas (LNG).
Inventors: |
Lee; Guang-Chung; (Houston,
TX) ; Golikeri; Sudhir; (Richmond, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Bechtel Hydrocarbon Technology Solutions, Inc. |
Houston |
TX |
US |
|
|
Family ID: |
52105509 |
Appl. No.: |
14/808620 |
Filed: |
July 24, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14763290 |
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PCT/US14/43183 |
Jun 19, 2014 |
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14808620 |
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61837162 |
Jun 19, 2013 |
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Current U.S.
Class: |
62/611 |
Current CPC
Class: |
F25J 1/0291 20130101;
F25B 2339/047 20130101; F25J 1/0022 20130101; F25J 1/0052 20130101;
F25J 2240/60 20130101; F25J 2240/70 20130101; F25B 2339/046
20130101; F25J 1/0227 20130101; F25B 1/08 20130101; F25B 2341/00
20130101; F25B 2341/0013 20130101; F25B 2341/0011 20130101; F25J
1/006 20130101; F25J 2240/82 20130101; F25J 1/0047 20130101; F25J
1/0283 20130101; F25J 2270/906 20130101; F25J 1/0212 20130101; F25B
2341/0014 20130101; F25B 2341/0012 20130101; F25B 9/08 20130101;
F25J 1/0297 20130101; F25J 1/0242 20130101 |
International
Class: |
F25J 1/00 20060101
F25J001/00 |
Claims
1. A supplemental cooling system for chilling a process feed gas,
which comprises: a liquid chiller ejector system; a steam input
line in fluid communication with the liquid chiller ejector system;
and a chilled liquid line wherein each end of the chilled liquid
line is in fluid communication with the liquid chiller ejector
system.
2. The system of claim 1, further comprising a heat exchanger
enclosing a portion of a process feed gas line and a portion of the
chilled liquid line, wherein the process feed gas line and the
chilled liquid line are positioned in sufficient proximity to each
other in the heat exchanger to affect heat transfer between the
process feed gas when it passes through the process feed gas line
and a chilled liquid when it passes through the chilled liquid
line.
3. The system of claim 2, wherein the heat exchanger encloses a
portion of a refrigeration intercooler line and a portion of a
refrigeration aftercooler line, the refrigeration intercooler line
and the refrigeration aftercooler line each positioned in
sufficient proximity to the process feed gas line and the chilled
liquid line in the heat exchanger to affect heat transfer between
the process feed gas when it passes through the process feed gas
line, the chilled liquid when it passes through the chilled liquid
line, a refrigeration intercooler when it passes through the
refrigeration intercooler line and a refrigeration aftercooler when
it passes through the refrigeration aftercooler line.
4. The system of claim 1, further comprising a heat exchanger
enclosing a portion of a single mixed refrigerant line and a
portion of the chilled liquid line, wherein the single mixed
refrigerant line and the chilled liquid line are positioned in
sufficient proximity to each other in the heat exchanger to effect
heat transfer between a single mixed refrigerant when it passes
through the single mixed refrigerant line and a chilled liquid when
it passes through the chilled liquid line.
5. The system of claim 1, further comprising a gas turbine engine
with an inlet air passage and enclosing a portion of the chilled
liquid line, wherein the inlet air passage and the chilled liquid
line are positioned in sufficient proximity to each other in the
gas turbine engine to affect heat transfer between inlet air when
it passes through the inlet air passage and a chilled liquid when
it passes through the chilled liquid line.
6. The system of claim 1, wherein the liquid chiller ejector system
comprises a steam ejector, a flash drum and a condenser.
7. The system of claim 6, wherein the steam ejector, the flash drum
and the condenser are in fluid communication with each other, the
steam ejector is connected to the steam input line and the flash
drum is connected to each end of the chilled liquid line.
8. A method for chilling a process feed gas using a supplemental
cooling system, which comprises: chilling a liquid to a temperature
of about 8.degree. C. to about 0.degree. C. in the supplemental
cooling system; circulating the chilled liquid through a chilled
liquid line, wherein each end of the chilled liquid line is in
fluid communication with the supplemental cooling system; chilling
the process feed gas in a heat exchanger as the process feed gas
passes through a portion of a process feed gas line in the heat
exchanger next to a portion of the chilled liquid line in the heat
exchanger; and sending the chilled process feed gas to a
liquefaction unit.
9. The method of claim 8, wherein the process feed gas line and the
chilled liquid line are positioned in sufficient proximity to each
other in the heat exchanger to affect heat transfer between the
process feed gas when it passes through the process feed gas line
and the chilled liquid when it passes through the chilled liquid
line.
10. The method of claim 8, wherein the liquid is chilled using
steam produced by one or more heat recovery generators.
11. The method of claim 10, wherein the one or more heat recovery
generators recover waste heat from a gas turbine engine.
12. The method of claim 8, wherein the process feed gas is chilled
to a temperature of about 12.degree. C. to about 15.degree. C.
13. The method of claim 8, further comprising chilling inlet air in
a gas turbine engine as the inlet air passes through an inlet air
passage in the gas turbine engine next to a portion of the chilled
liquid line in the gas turbine engine.
14. The method of claim 13, wherein the inlet air passage and the
chilled liquid line are position in sufficient proximity to each
other in the gas turbine engine to affect heat transfer between the
inlet air when it passes through the inlet air passage and the
chilled liquid when it passes through the chilled liquid line.
15. A method for chilling a process feed gas using a supplemental
cooling system, which comprises: chilling a liquid to a temperature
of about 8.degree. C. to about 0.degree. C.; sending the chilled
liquid to a process vessel; and chilling the process feed gas in a
heat exchanger positioned within the process vessel as the process
feed gas passes through a portion of a process feed gas line in the
heat exchanger next to a portion of a chilled liquid line in the
heat exchanger.
16. The method of claim 15, wherein the process feed gas is chilled
to a temperature of about 12.degree. C. to about 15.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/763,290 which is incorporated herein by
reference, and claims the priority from PCT Patent Application
Serial No. PCT/US14/43183, filed on Jun. 19, 2014, which claims
priority from U.S. Provisional Patent Application Ser. No.
61/837,162, filed on Jun. 19, 2013, which are incorporated herein
by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
[0002] Not applicable.
FIELD OF THE DISCLOSURE
[0003] The present disclosure generally relates to systems and
methods for natural gas liquefaction capacity augmentation. More
particularly, the present disclosure relates to natural gas
liquefaction capacity augmentation using supplemental cooling
systems and methods to improve the efficiency of a liquefaction
cycle for producing liquefied natural gas (LNG).
BACKGROUND
[0004] Process feed gas in an LNG plant generally goes through a
series of pre-treatment stages to remove acid gas, mercury and
moisture and avoid freezing or corrosion problems in the cryogenic
section. A generic single mixed refrigerant (SMR) liquefaction
cycle may be used to cool and liquefy process feed gas such as, for
example, natural gas. The process feed gas typically passes through
a heat exchanger with the SMR for cooling the process feed gas that
is used for producing LNG. The SMR is cooled using a primary
cooling system comprising water at a temperature that is around
25.degree. C. The primary cooling system may include one or more
heat exchangers for cooling the SMR with the cooling water before
it passes through the heat exchanger with the process feed gas. The
SMR liquefaction cycle may include one or more compressors for
circulating the SMR through the one or more heat exchangers and a
separator. The compressors are typically driven by a gas turbine
engine that produces waste heat in the form of a hot combusted
gas.
[0005] A generic SMR liquefaction cycle requires about 40 MW to
produce 1 million tons per annum (MTPA) of LNG. If the process feed
gas was cooler, then the amount of LNG produced may be increased or
the same amount of LNG may be produced with less energy
consumption. In addition, the cooling water used in the primary
cooling system and the waste heat from the gas turbine are not
recycled or used in any supplemental manner to improve the
efficiency of a liquefaction cycle for producing LNG.
SUMMARY OF THE DISCLOSURE
[0006] The present disclosure overcomes one or more deficiencies in
the prior art by providing systems and methods for natural gas
liquefaction capacity augmentation using supplemental cooling
systems and methods to improve the efficiency of a liquefaction
cycle for producing LNG.
[0007] In one embodiment, the present disclosure includes a
supplemental cooling system for chilling a process feed gas, which
comprises: i) a liquid chiller ejector system; ii) a steam input
line in fluid communication with the liquid chiller ejector system;
and iii) a chilled liquid line wherein each end of the chilled
liquid line is in fluid communication with the liquid chiller
ejector system.
[0008] In another embodiment, the present disclosure includes a
method for chilling a process feed gas using a supplemental cooling
system, which comprises: i) chilling a liquid to a temperature of
about 8.degree. C. to about 0.degree. C. in the supplemental
cooling system; ii) circulating the chilled liquid through a
chilled liquid line, wherein each end of the chilled liquid line is
in fluid communication with the supplemental cooling system; iii)
chilling the process feed gas in a heat exchanger as the process
feed gas passes through a portion of a process feed gas line in the
heat exchanger next to a portion of the chilled liquid line in the
heat exchanger; and (iv) sending the chilled process feed gas to a
liquefaction unit.
[0009] In yet another embodiment, the present disclosure includes a
method for a method for chilling a process feed gas using a
supplemental cooling system, which comprises: i) chilling a liquid
to a temperature of about 8.degree. C. to about 0.degree. C.; ii)
sending the chilled liquid to a process vessel; and iii) chilling
the process feed gas in a heat exchanger positioned within the
process vessel as the process feed gas passes through a portion of
a process feed gas line in the heat exchanger to a portion of a
chilled liquid line in the heat exchanger.
[0010] Additional aspects, advantages and embodiments of the
disclosure will become apparent to those skilled in the art from
the following description of the various embodiments and related
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The present disclosure is described below with references to
the accompanying drawings in which like elements are referenced
with like reference numerals, and in which:
[0012] FIG. 1 is a schematic diagram illustrating one embodiment of
a supplemental cooling system used in a liquefaction cycle
according to the present disclosure.
[0013] FIG. 2 is a graph illustrating the power output of a gas
turbine engine used in the supplemental cooling system of FIG. 1 at
various inlet air temperatures.
[0014] FIG. 3 is a schematic diagram illustrating another
embodiment of a supplemental cooling system used in another
liquefaction cycle according to the present disclosure.
[0015] FIG. 4 is a schematic diagram illustrating the supplemental
cooling system in FIG. 3 used in another liquefaction cycle
according to the present disclosure.
[0016] FIG. 5 is a schematic diagram illustrating the supplemental
cooling system in FIG. 3 used in another liquefaction cycle
according to the present disclosure.
[0017] FIG. 6 is a schematic diagram illustrating another
embodiment of a supplemental cooling system used in another
liquefaction cycle according to the present disclosure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The subject matter of the present disclosure is described
with specificity, however, the description itself is not intended
to limit the scope of the disclosure. The subject matter thus,
might also be embodied in other ways, to include different steps or
combinations of steps similar to the ones described herein, in
conjunction with other present or future technologies. Moreover,
although the term "step" may be used herein to describe different
elements of methods employed, the term should not be interpreted as
implying any particular order among or between various steps herein
disclosed unless otherwise expressly limited by the description to
a particular order. While the present disclosure may be applied in
the oil and gas industry, it is not limited thereto and may also be
applied in other industries to achieve similar results.
[0019] The following description refers to FIGS. 1-6, which
includes systems and methods for natural gas liquefaction capacity
augmentation using supplemental cooling systems to improve the
efficiency of a liquefaction cycle for producing LNG. In FIGS. 1-6,
various embodiments of a supplemental cooling system are
illustrated in different exemplary liquefaction cycles. The
supplemental cooling system embodiments may be characterized as
either a chilled water loop system illustrated in FIGS. 1-5 or a
direct chilled water system illustrated in FIG. 6. Although chilled
water is the primary or preferred fluid component in each
supplemental cooling system, other fluids may be used instead. Each
system may be easily extended to liquefaction cycles other than
those illustrated and may use one or more conventional heat
exchangers to affect heat transfer between a process feed gas and
the supplemental cooling system. The pressures and temperatures
described below are exemplary and only for purposes of
illustration.
[0020] Referring now to FIG. 1, a schematic diagram illustrates one
embodiment of a supplemental cooling system 100 used in a generic
SMR liquefaction cycle according to the present disclosure. The
supplemental cooling system 100 uses steam 102 produced by one or
more conventional heat recovery steam generators 104 to produce
water chilled to a temperature of about 8.degree. C. to about
0.degree. C. A pressure for the steam 102 as low as 3 barg can be
used to drive the supplemental cooling system 100, although it
becomes incrementally more efficient at higher pressures. Each heat
recovery steam generator 104 is driven by boiler feed water 106 and
hot combusted gas 108 from a conventional gas turbine engine 110. A
steam condensate 101 leaves the supplemental cooling system 100 and
may be used to produce the boiler feed water 106.
[0021] The SMR liquefaction cycle includes the SMR 112, which is
used to cool process feed gas 114 to a temperature of about
-160.degree. C. as each passes through a conventional primary heat
exchanger 116. The SMR 112 is circulated in a closed loop at a
temperature of about 12.degree. C. The SMR 112 is cooled to
12.degree. C. using a primary cooling system and the supplemental
cooling system 100. The primary cooling system comprises water 118
at a temperature above about 25.degree. C., The primary cooling
system may include one or more conventional secondary heat
exchangers 120 for cooling the SMR 112 with the water 118 before it
passes through the primary heat exchanger 116 with the process feed
gas 114. The SMR liquefaction cycle also includes a conventional
separator 122 for separating the SMR 112 into a SMR gas 124 and SMR
liquid 126. The SMR gas 124 leaves the separator 122 and enters a
compressor 128. The SMR liquid 126 leaves the separator 122 and is
merged with the SMR 112 leaving the compressor 128 because the
compressor 128 will not accept the SMR liquid 126. Thus, the
separator 122 is needed to separate the SMR liquid 126 from the SMR
112. A pump 130 may be used to merge the SMR liquid 126 with the
SMR 112. Another compressor 132 may be used to raise the pressure
enough to maintain circulation of the SMR 112. The compressors 128,
132 are driven by the gas turbine engine 110 that produces waste
heat in the form of the hot combusted gas 108.
[0022] The supplemental cooling system 100 produces one or more
chilled water streams at a temperature of about 8.degree. C. to
about 0.degree. C. Here, there are three (3) chilled water streams
140, 142 and 143. Stream 140 is used to chill the process feed gas
114 to a temperature of about 12.degree. C. as each passes through
a conventional supplemental heat exchanger 146. In this manner, the
process feed gas 114 is pre-cooled to a temperature of about
12.degree. C. by the stream 140 using the supplemental heat
exchanger 146 before it enters the primary heat exchanger 116 where
it is further cooled and liquefied to a temperature of about
-160.degree. C. by the SMR 112 using the primary heat exchanger
116. Alternatively, stream 140 may be used to chill the process
feed gas 114 as each passes through the primary heat exchanger 116.
In other words, stream 140 may pass directly through the primary
heat exchanger 116 thus, eliminating the need for the supplemental
heat exchanger 146. Stream 142 is used to chill the SMR 112 as each
passes through the secondary heat exchangers 120. Stream 142 is
thus, split into two streams, one for each secondary heat
exchanger. Alternatively, an additional chilled water stream may be
produced by the supplemental cooling system 100 to chill the SMR
112 as each passes through one of the secondary heat exchangers
120. Stream 144 is used to chill inlet air 146 from about
30.degree. C. to 40.degree. C. (ambient) to about 12.degree. C. as
each passes through the gas turbine engine 110 using techniques and
equipment well known in the art. Each stream 140, 142, and 144 is
returned to the supplemental cooling system 100 at a temperature of
about 25.degree. C. to 32.degree. C. where it is chilled back down
to a temperature of about 8.degree. C. to about 0.degree. C. using
steam 102 produced by one or more conventional heat recovery steam
generators 104. Various designs and equipment are commercially
available to use in the supplemental cooling system 100 to produce
chilled water through steam driven ejectors. For example, a
standard steam ejector, flash drum and condenser may be used in the
supplemental cooling system 100 as described in reference to FIGS.
3-5.
[0023] A generic SMR liquefaction cycle requires about 40 MW to
produce 1 MTPA of LNG. With the supplemental cooling system 100,
the power requirement for producing 1 MTPA LNG may be reduced to
about 32 MW, which is a 20% power requirement reduction. Using the
same gas turbine engine 110 and 40 MW power requirement thus, may
be expected to produce 1.4 MTPA LNG, which is a 40% increase in LNG
production. In FIG. 2, a graph illustrates the anticipated power
output of a gas turbine engine (e.g. General Electric
aero-derivative LM6000) used in the supplemental cooling system 100
of FIG. 1 at various inlet air temperatures. As can be seen by FIG.
2, lowering the inlet air temperature may increase the power output
from about 32 MW at 30.degree. C. (ambient) to about 45 MW at
12.degree. C. (chilled inlet air).
[0024] Referring now to FIG. 3, a schematic diagram illustrates
another embodiment of a supplemental cooling system 300 used in
another liquefaction cycle according to the present disclosure. A
primary cooling system includes a refrigeration aftercooler 310, a
refrigeration intercooler 312 and a conventional multi-stream heat
exchanger 302 (for compactness and high efficiency) that are used
with the supplemental cooling system 300 to cool the process feed
gas 314 to a temperature of about 12.degree. C. as each passes
through the multi-stream heat exchanger 302. Otherwise, the process
feed gas 314 would only be cooled to about 30.degree. C. to
32.degree. C. if only the refrigeration aftercooler 310 and the
refrigeration intercooler 312 were used. The multi-stream heat
exchanger 302 is a plate-fin type heat exchanger, however, may be a
wound-coil type heat exchanger. The supplemental cooling system 300
comprises a steam ejector 304, a flash drum 306 and a condenser
308. The flash drum 306 produces a chilled water stream 316 at a
temperature of about 8.degree. C. to about 0.degree. C. The chilled
water stream 316 is used with the refrigeration aftercooler 310 and
the refrigeration intercooler 312 to chill the process feed gas 314
to a temperature of about 12.degree. C. as each passes through the
multi-stream heat exchanger 302. The chilled water stream 316
inside the multi-stream heat exchanger 302 absorbs heat from the
process feed gas 314, the refrigeration aftercooler 310, and the
refrigeration intercooler 312, and becomes partially vaporized
before recirculating back to the flash drum 306 as a two-phase
vapor and liquid stream 318. A resulting vapor stream 320
comprising water vapor inside the flash drum 306 is continuously
removed by the steam ejector 304. The steam ejector 304 uses steam
322 from one or more conventional heat recovery steam generators
(not shown) to discharge another vapor stream 324 from the steam
ejector 304. The another vapor stream 324 is sent to the condenser
308 where it is totally condensed. A portion of the condensate 326
may be recirculated back to the flash drum 306 and another portion
of the condensate 328 may be sent to one or more conventional heat
recovery steam generators (not shown) for steam generation from gas
turbine waste heat.
[0025] Referring now to FIG. 4, a schematic diagram illustrates the
supplemental cooling system 300 in FIG. 3 used in another
liquefaction cycle according to the present disclosure. The
supplemental cooling system 300 comprises a steam ejector 304, a
flash drum 306 and a condenser 308. The flash drum 306 produces a
chilled water stream 316 at a temperature of about 8.degree. C. to
about 0.degree. C. The chilled water stream 316 is used to chill
the process feed gas 314 to a temperature of about 15.degree. C. as
each passes through a knock back condenser 402, which may also be
referred to as a reflux condenser or dephlegmator. The chilled
water stream 316 inside the knock back condenser 402 absorbs heat
from the process feed gas 314 and becomes partially vaporized after
leaving the knock back condenser 402 before recirculating back to
the flash drum 306 as a two-phase vapor and liquid stream 318 at
about 32.degree. C. A resulting vapor stream 320 comprising water
vapor inside the flash drum 306 is continuously removed by the
steam ejector 304. The steam ejector 304 uses steam 322 from one or
more conventional heat recovery steam generators (not shown) to
discharge another vapor stream 324 from the steam ejector 304. The
another vapor stream 324 is sent to the condenser 308 where it is
totally condensed. A portion of the condensate 326 may be
recirculated back to the flash drum 306 and another portion of the
condensate 328 may be sent to one or more conventional heat
recovery steam generators (not shown) for steam generation from gas
turbine waste heat. The process feed gas 314 leaves an acid gas
absorber 404 at about 45.degree. C. and is sent to a separator 406.
The process feed gas 314 leaves the separator 406 and is sent to
the knock-back condenser 402. An amine solvent 405 also leaves the
separator 406. In the knock back condenser 402, a water-rich liquid
phase stream 408 is formed and returns back to the separator 406.
The process feed gas 314 leaving the knock-back condenser 402 has a
significantly lower moisture content and is nearly free of amine.
It is also possible to use a conventional shell-and-tube type heat
exchanger or other forms of heat exchangers, such as plate-fin heat
exchanger, to replace the knock-back condenser with slightly lower
separation efficiency.
[0026] As demonstrated by the placement of the supplemental cooling
system 300 illustrated in FIG. 4, the process feed gas 314 is
pre-cooled downstream from the acid gas absorber 404 before
entering a dehydration unit. The process feed gas 314 may also be
pre-cooled downstream from a dehydration or mercury removal unit
(not shown) before entering a liquefaction unit (not shown) using
the same supplemental cooling system 300. One of the advantages of
pre-cooling a process feed gas before entering a dehydration unit
is that, as the process feed gas temperature is reduced, the
moisture content is also reduced thus, unloading the dehydration
unit and minimizing amine loss from the acid gas absorber. This can
result in reduced capital cost and operating cost.
[0027] Referring now to FIG. 5, a schematic diagram illustrates the
supplemental cooling system 300 in FIG. 3 used in another
liquefaction cycle according to the present disclosure. The
supplemental cooling system 300 comprises a steam ejector 304, a
flash drum 306 and a condenser 308. The flash drum 306 produces a
chilled water stream 316 at a temperature of about 8.degree. C. to
about 0.degree. C. The chilled water stream 316 is used to chill
inlet air 502 at an ambient temperature flowing through a gas
turbine engine 504 to a temperature of about 12.degree. C. as each
passes through the gas turbine engine 504. The inlet air 502 acts
as the primary cooling system for the gas turbine engine 504. The
chilled water stream 316 inside the gas turbine engine 504 absorbs
heat from the inlet air 502 and becomes partially vaporized before
recirculating back to the flash drum 306 as a two-phase vapor and
liquid stream 318. A resulting vapor stream 320 comprising water
vapor inside the flash drum 306 is continuously removed by the
steam ejector 304, The steam ejector 304 uses steam 322 from one or
more conventional heat recovery steam generators (not shown) to
discharge another vapor stream 324 from the steam ejector 304. The
another vapor stream 324 is sent to the condenser 308 where it is
totally condensed. A portion of the condensate 326 may be
recirculated back to the flash drum 306 and another portion of the
condensate 328 may be sent to one or more conventional heat
recovery steam generators (not shown) for steam generation using
the waste heat (exhaust air) 506 from the gas turbine engine 504.
Depending on the temperature of the chilled water stream 316, a
multi-stage steam ejector design may be employed.
[0028] Referring now to FIG. 6, a schematic diagram illustrates
another embodiment of a supplemental cooling system 600 used in
another liquefaction cycle according to the present disclosure. The
primary cooling system includes a refrigeration aftercooler 602, a
refrigeration intercooler 604 and a multi-stream heat exchanger 608
that are used with the supplemental cooling system 600 to cool the
process feed gas 606 to a temperature of about 12.degree. C. as
each passes through the multi-stream heat exchanger 608. Otherwise,
the process feed gas 606 would only be cooled to about 30.degree.
C. to 32.degree. C. if only the refrigeration aftercooler 602 and
the refrigeration intercooler 604 were used. The multi-stream heat
exchanger 608 is a plate-fin type heat exchanger, however, may be a
wound-coil type heat exchanger. The supplemental cooling system 600
comprises a process vessel 610 and a steam ejector 612. A chilled
water stream 614 is sent to the process vessel 610 at a temperature
of about 8.degree. C. to about 0.degree. C. The chilled water in
the process vessel 610 is used with the refrigeration aftercooler
602 and the refrigeration intercooler 604 to chill the process feed
gas 606 in the multi-stream heat exchanger 608 to a temperature of
about 12.degree. C. The chilled water in the process vessel 610
absorbs heat from the multi-stream heat exchanger 608 and other
heat sources (e.g. the refrigeration aftercooler 602, refrigeration
intercooler 604, process feed gas 606), which is continuously
vaporized at a constant pressure. Thus, there is preferably a
continuous supply of the chilled water stream 614 to maintain
chilled water in the process vessel 610. The vaporization of the
chilled water is at a reduced pressure such that the water
temperature is maintained. The generated vapor is continuously
removed by the steam ejector 612 to maintain the reduced pressure
in the process vessel 610. In this way, the heat exchange between
the chilled water and the heat sources takes advantage of the
constant temperature of latent heat during water vaporization.
Therefore, the overall heat exchanger surface requirement will be
smaller, thus saving capital cost. The steam ejector 612 uses steam
616 from one or more conventional heat recovery steam generators
(not shown) to discharge a vapor stream 618 from the steam ejector
304. This embodiment may also be referred to as using
"core-in-kettle" technology for compactness and high heat exchanger
efficiency. Depending on the temperature of the chilled water
stream 614, a multi-stage steam ejector design may be employed. The
process vessel 610 may be positioned horizontally or
vertically.
[0029] While the present disclosure has been described in
connection with presently preferred embodiments, it will be
understood by those skilled in the art that it is not intended to
limit the disclosure to those embodiments. It is therefore,
contemplated that various alternative embodiments and modifications
may be made to the disclosed embodiments without departing from the
spirit and scope of the disclosure defined by the appended claims
and equivalents thereof
* * * * *