U.S. patent application number 11/184282 was filed with the patent office on 2006-07-20 for operating system of liquefied natural gas ship for sub-cooling and liquefying boil-off gas.
Invention is credited to Hyung-Su An, Hyun-Jin Kim, Nam-Su Kim, Hyun-Ki Park, Jin-Yeol Yun.
Application Number | 20060156758 11/184282 |
Document ID | / |
Family ID | 36636849 |
Filed Date | 2006-07-20 |
United States Patent
Application |
20060156758 |
Kind Code |
A1 |
An; Hyung-Su ; et
al. |
July 20, 2006 |
Operating system of liquefied natural gas ship for sub-cooling and
liquefying boil-off gas
Abstract
An operating system of a liquefied natural gas ship for
performing sub-cooled liquefaction of boil-off gas includes a
boil-off gas compressor, a cryogenic heat exchanger connected to a
refrigerator system, and a first check valve and a first pressure
control valve, installed in a pipe between a liquefied natural gas
phase separator and a gas combustion unit, and a second check valve
and a second pressure control valve, installed in a parallel pipe
connected to the pipe in parallel. The parallel pipe is connected
to a pipe between the boil-off gas compressor and the cryogenic
heat exchanger such that boil-off gas is supplied to an upper vapor
region of the liquefied natural gas phase separator. Thus, pressure
and level of the liquefied natural gas phase separator are stably
controlled. Power consumption is effectively reduced, and
economical efficiency is achieved by stable operating pressure and
level of the liquefied natural gas phase separator.
Inventors: |
An; Hyung-Su; (Geoje-si,
KR) ; Kim; Nam-Su; (Suwon-si, KR) ; Yun;
Jin-Yeol; (Geoje-si, KR) ; Kim; Hyun-Jin;
(Gwangju-si, KR) ; Park; Hyun-Ki; (Geoje-si,
KR) |
Correspondence
Address: |
HOFFMANN & BARON, LLP
6900 JERICHO TURNPIKE
SYOSSET
NY
11791
US
|
Family ID: |
36636849 |
Appl. No.: |
11/184282 |
Filed: |
July 19, 2005 |
Current U.S.
Class: |
62/613 |
Current CPC
Class: |
F25J 2230/60 20130101;
F25J 1/0292 20130101; F25J 1/0025 20130101; B63B 25/16 20130101;
F25J 1/005 20130101; F25J 2245/42 20130101; F25J 2220/62 20130101;
F25J 1/0277 20130101; F25J 1/0072 20130101; F25J 2205/02 20130101;
F25J 1/0208 20130101; F25J 2205/30 20130101; F25J 2245/02 20130101;
F25J 2210/04 20130101; F25J 1/0045 20130101; F25J 1/0245 20130101;
F25J 2230/08 20130101 |
Class at
Publication: |
062/613 |
International
Class: |
F25J 1/00 20060101
F25J001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 18, 2005 |
KR |
10-2005-0004649 |
Jan 18, 2005 |
KR |
10-2005-0004650 |
Claims
1. An operating system of a liquefied natural gas ship for
performing sub-cooled liquefaction of boil-off gas for
re-liquefaction comprising a boil-off gas compressor, a cryogenic
heat exchanger connected to a refrigerator system, and a first
check valve and a first pressure control valve, installed in a pipe
connecting a liquefied natural gas phase separator with a gas
combustion unit, the operating system further comprising: a
parallel pipe connected to the pipe for connecting the liquefied
natural gas phase separator with the first check valve in parallel
and having the same structure as that of the pipe in which the
first check valve and the first pressure control valve are
installed; a second check valve installed in the parallel pipe and
preventing reverse flow of gas generated when pressure of the pipe
is abnormally increased; and a second pressure control valve
installed in the parallel pipe and maintaining a predetermined
pressure of the liquefied natural gas phase separator by adjusting
a quantity of boil-off gas generated by the boil-off gas compressor
such that the liquefied natural gas phase separator, operated
tinder the sub-cooling condition, is stably operated; wherein an
end of the parallel pipe is connected to a pipe between the
boil-off gas compressor and the cryogenic heat exchanger such that
boil-off gas, discharged from the boil-off gas compressor, is
supplied to an upper vapor region of the liquefied natural gas
phase separator for the purpose of blanket during sub-cooling
liquefying operation, so that pressure and level of liquefied
natural gas of the liquefied natural gas phase separator are stably
controlled.
2. An operating system of a liquefied natural gas ship for
performing sub-cooled liquefaction of boil-off gas for
re-liquefaction comprising a boil-off gas compressor, a cryogenic
heat exchanger connected to a refrigerator system, and a first
check valve and a first pressure control valve, installed in a pipe
connecting a liquefied natural gas phase separator with a gas
combustion unit, the operating system further comprising: a
parallel pipe connected to the pipe for connecting the liquefied
natural gas phase separator with the first check valve in parallel
and having the same structure as that of the pipe in which the
first check valve and the first pressure control valve are
installed; a nitrogen generator connected to the parallel pipe and
installed in a machinery space of the liquefied natural gas ship
and to supply nitrogen gas to the liquefied natural gas phase
separator, operated under the sub-cooling condition, for the
purpose of maintaining a predetermined pressure of the liquefied
natural gas phase separator; a second check valve for preventing
reverse flow generated when pressure of the pipe is abnormally
increased; and a second pressure control valve for maintaining a
predetermined pressure of the liquefied natural gas phase separator
by adjusting a quantity of nitrogen gas for the purpose of stable
operation of the liquefied natural gas phase separator operated
under the sub-cooling condition; wherein nitrogen gas is supplied
from the nitrogen generator to a vapor region of the liquefied
natural gas phase separator for the purpose of blanket during the
sub-cooled liquefaction, so that pressure and level of liquefied
natural gas of the liquefied natural gas phase separator are stably
controlled.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an operating system of a
liquefied natural gas ship for sub-cooling and liquefying boil-off
gas, and more particularly, to an operating system of a liquefied
natural gas ship for sub-cooling and liquefying boil-off gas in
which a re-liquefaction system of boil-off gas in a liquefied
natural gas ship is modified into an efficient sub-cooling and
liquefaction structure so that power consumption is reduced,
operation is simply performed, and economic efficiency can be
achieved.
[0003] 2. Description of the Related Art
[0004] Generally, boil-off gas generated from a cargo tank is
re-liquefied into liquefied natural gas using a re-liquefaction
system installed in a compressor and motor room of a liquefied
natural gas ship, and the re-liquefied boil-off gas is returned
back to the cargo tank.
[0005] There are several basic operating systems in the
re-liquefaction system, such as partial liquefaction, saturated
liquefaction, sub-cooled liquefaction, and the like. The sub-cooled
liquefaction is superior to the others in view of power
consumption, simple operation, etc., and the present invention
provides an operating system for sub-cooled liquefaction of
boil-off gas adapted to have a more efficient structure.
SUMMARY OF THE INVENTION
[0006] Therefore, the present invention has been made in view of
the above and/or other problems, and it is an object of the present
invention to provide an operating system of a liquefied natural gas
ship for sub-cooling and liquefying boil-off gas in which a
re-liquefaction system of boil-off gas in a liquefied natural gas
ship is modified into an efficient sub-cooling and liquefaction
structure so that power consumption is reduced, operation is simply
performed, and economical efficiency can be achieved.
[0007] In accordance with the present invention, the above and
other objects can be accomplished by the provision of an operating
system of a liquefied natural gas ship for performing sub-cooled
liquefaction of boil-off gas for re-liquefaction including a
boil-off gas compressor, a cryogenic heat exchanger connected to a
refrigerator system, and a first check valve and a first pressure
control valve, installed in a pipe connecting a liquefied natural
gas phase separator with a gas combustion unit, the operating
system further including: a parallel pipe connected to the pipe for
connecting the liquefied natural gas phase separator with the first
check valve in parallel and having the same structure as that of
the pipe in which the first check valve and the first pressure
control valve are installed; a second check valve installed in the
parallel pipe and preventing reverse flow of gas generated when
pressure of the pipe is abnormally increased; and a second pressure
control valve installed in the parallel pipe and maintaining a
predetermined pressure of the liquefied natural gas phase separator
by adjusting a quantity of boil-off gas generated by the boil-off
gas compressor such that the liquefied natural gas phase separator,
operated under the sub-cooling condition, is stably operated;
wherein an end of the parallel pipe is connected to a pipe between
the boil-off gas compressor and the cryogenic heat exchanger such
that boil-off gas, discharged from the boil-off gas compressor, is
supplied to an upper vapor region of the liquefied natural gas
phase separator for the purpose of blanket during sub-cooling
liquefying operation, so that pressure and level of liquefied
natural gas of the liquefied natural gas phase separator are stably
controlled.
[0008] In accordance with the present invention, the above and
other objects can be accomplished by the provision of an operating
system of a liquefied natural gas ship for performing sub-cooled
liquefaction of boil-off gas for re-liquefaction including a
boil-off gas compressor, a cryogenic heat exchanger connected to a
refrigerator system, and a first check valve and a first pressure
control valve, installed in a pipe connecting a liquefied natural
gas phase separator with a gas combustion unit, the operating
system further including: a parallel pipe connected to the pipe for
connecting the liquefied natural gas phase separator with the first
check valve in parallel and having the same structure as that of
the pipe in which the first check valve and the first pressure
control valve are installed; a nitrogen generator connected to the
parallel pipe and installed in a machinery space of the liquefied
natural gas ship and to supply nitrogen gas to the liquefied
natural gas phase separator, operated under the sub-cooling
condition, for the purpose of maintaining a predetermined pressure
of the liquefied natural gas phase separator; a second check valve
for preventing reverse flow generated when pressure of the pipe is
abnormally increased; and a second pressure control valve for
maintaining a predetermined pressure of the liquefied natural gas
phase separator by adjusting a quantity of nitrogen gas for the
purpose of stable operation of the liquefied natural gas phase
separator operated under the sub-cooling condition; wherein
nitrogen gas is supplied from the nitrogen generator to a vapor
region of the liquefied natural gas phase separator for the purpose
of blanket during the sub-cooled liquefaction, so that pressure and
level of liquefied natural gas of the liquefied natural gas phase
separator are stably controlled.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The object and advantages of the present invention will
become apparent and more readily appreciated from the following
description of an embodiment, taken in conjunction with the
accompanying drawings, in which:
[0010] FIG. 1 is a schematic system diagram illustrating an
operating system for performing sub-cooled liquefaction of boil-off
gas in a liquefied natural gas ship according to a preferred
embodiment of the present invention;
[0011] FIG. 2 is a schematic system diagram illustrating an
operating system for performing sub-cooled liquefaction of boil-off
gas in a liquefied natural gas ship according to another preferred
embodiment of the present invention; and
[0012] FIG. 3 is a table comparing operation according to the
operating system for performing sub-cooled liquefaction of boil-off
gas in a liquefied natural gas ship of the present invention with
operation according to a conventional operation system for
performing saturated liquefaction of boil-off gas in a liquefied
natural gas ship.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] An operating system of a liquefied natural gas ship for
performing sub-cooled liquefaction of boil-off gas for
re-liquefaction according to a first preferred embodiment of the
present invention includes a boil-off gas compressor 10, a
cryogenic heat exchanger 20 connected to a refrigerator system 40
and a check valve 50, and a pressure control valve 60, installed in
a pipe connecting a liquefied natural gas phase separator 30 with a
gas combustion unit 80. The operating system of a liquefied natural
gas ship further includes a parallel pipe connected to a pipe for
connecting the liquefied natural gas phase separator 30 with the
check valve 50 in parallel and has the same structure as that of
the pipe in which the check valve 50 and the pressure control valve
60 are installed. The parallel pipe includes a check valve 50' for
preventing reverse flow of gas generated when pressure of the pipe
is abnormally increased, and a pressure control valve 60' for
maintaining a predetermined pressure of the liquefied natural gas
phase separator 30 by adjusting the quantity of boil-off gas
generated by the boil-off gas compressor 10 such that the liquefied
natural gas phase separator 30, operated under the sub-cooling
condition, is stably operated. An end of the parallel pipe is
connected to a pipe between the boil-off gas compressor 10 and the
cryogenic heat exchanger 20 such that boil-off gas, discharged from
the boil-off gas compressor 10, is supplied to an upper vapor
region of the liquefied natural gas phase separator 30 for the
purpose of blanket during sub-cooling liquefying operation, so that
pressure and level of liquefied natural gas of the liquefied
natural gas phase separator 30 are stably controlled.
[0014] Moreover, an operating system of a liquefied natural gas
ship for performing sub-cooled liquefaction of boil-off gas for
re-liquefaction according to a second preferred embodiment of the
present invention includes a boil-off gas compressor 10, a
cryogenic heat exchanger 20 connected to a refrigerator system 40,
and a check valve 50 and a pressure control valve 60, installed in
a pipe connecting a liquefied natural gas phase separator 30 with a
gas combustion unit 80. The operating system of a liquefied natural
gas ship further includes a parallel pipe connected to a pipe for
connecting the liquefied natural gas phase separator 30 with the
check valve 50 in parallel and has the same structure as that of
the pipe in which the check valve 50 and the pressure control valve
60 are installed. The parallel pipe is connected to a nitrogen
generator 70 installed in a machinery space of the liquefied
natural gas ship and serves to supply nitrogen gas to the liquefied
natural gas phase separator 30, operated under the sub-cooling
condition, for the purpose of maintaining a predetermined pressure
of the liquefied natural gas phase separator 30, and includes a
check valve 50' for preventing reverse flow generated when pressure
of the pipe is abnormally increased and a pressure control valve
60' for maintaining a predetermined pressure of the liquefied
natural gas phase separator 30 by adjusting the quantity of
nitrogen gas for the purpose of stable operation of the liquefied
natural gas phase separator 30 operated under the sub-cooling
condition. Thus, nitrogen gas is supplied from the nitrogen
generator 70 to a vapor region of the liquefied natural gas phase
separator 30 for the purpose of blanket during the sub-cooled
liquefaction, so that pressure and level of liquefied natural gas
of the liquefied natural gas phase separator 30 are stably
controlled.
[0015] Elements of the operating system of a liquefied natural gas
ship for performing sub-cooled liquefaction of boil-off gas for
re-liquefaction according to the first preferred embodiment of the
present invention will be described in detail with reference to
FIG. 1 as follows.
[0016] The boil-off gas compressor 10 compresses boil-off gas
generated by a cargo tank of the liquefied natural gas ship at a
predetermined pressure and supplies the same to the cryogenic heat
exchanger 20 for the purpose of stable re-liquefaction of boil-off
gas.
[0017] The cryogenic heat exchanger 20 performs heat exchange
between the boil-off gas compressed at the predetermined pressure
and cold refrigerant introduced from the refrigerator system 40 to
liquefy the compressed boil-off gas.
[0018] The liquefied natural gas phase separator 30 connected to
the cryogenic heat exchanger 20 serves as a buffer tank for stably
returning liquefied natural gas liquefied by the cryogenic heat
exchanger 20 to the cargo tank. Meanwhile, since a predetermined
pressure and a predetermined level of liquefied natural gas are
maintained, a level control valve 90 for maintaining a
predetermined level of liquefied natural gas is connected to the
liquefied natural gas phase separator 30.
[0019] In order to sub-cool boil-off gas, a specific quantity of
refrigerant having a specific temperature is required. A
refrigerator system 40, serving as a refrigerator system for
producing the required refrigerant, includes compressors, coolers,
and a turbo-expander and is connected to the cryogenic heat
exchanger 20.
[0020] The liquefied natural gas phase separator 30 is connected to
the check valve 50 for preventing reverse flow generated when
pressure of the gas combustion unit 80 is abnormally increased, and
the pressure control valve 60 for maintaining a predetermined
pressure of the liquefied natural gas phase separator 30 by
discharging flash gas generated by the liquefied natural gas phase
separator 30 when flash gas is generated and pressure is increased
due to the abnormal operation of the liquefied natural gas phase
generator 30.
[0021] The gas combustion unit 80 oxidizes the flash gas generated
by the liquefied natural gas phase separator 30 when flash gas is
generated and pressure thereof is increased due to the abnormal
operation of the liquefied natural gas phase separator 30 so as to
maintain the predetermined pressure of the liquefied natural gas
phase separator 30.
[0022] Particularly, the operating system of a liquefied natural
gas ship for performing sub-cooled liquefaction of boil-off gas for
re-liquefaction according to the first preferred embodiment of the
present invention includes the parallel pipe having the same
structure as the structure in which the check valve 50 and the
pressure control valve 60 are installed in the pipe between the
liquefied natural gas phase separator 30 and the check valve 50.
The parallel pipe includes the check valve 50' for preventing
reverse flow generated due to the abnormal pressure increase, and
the pressure control valve 60' for maintaining the predetermined
pressure of the liquefied natural gas phase separator 30 by
adjusting the quantity of boil-off gas generated by the boil-off
gas compressor 10 such that the liquefied natural gas phase
separator 30, operated under the sub-cooling condition, is stably
operated. The end of the parallel pipe is connected to a pipe
between the boil-off gas compressor 10 and the cryogenic heat
exchanger 20 such that boil-off gas, discharged from the boil-off
gas compressor 10, is supplied to the upper vapor region of the
liquefied natural gas phase separator 30 for the purpose of blanket
during sub-cooling liquefying operation, so that pressure and level
of liquefied natural gas of the liquefied natural gas phase
separator 30 are stably controlled.
[0023] The operating system according to the first preferred
embodiment of the present invention supplies boil-off gas
discharged from the boil-off gas compressor 10 to the vapor region
of the liquefied natural gas phase separator 30 for the purpose of
blanket such that pressure and level of the liquefied natural gas
of the liquefied natural gas phase separator 30 are stably
controlled.
[0024] In the operating system according to the first preferred
embodiment of the present invention, boil-off gas of about -100
degrees centigrade, 0.05 bar, g, 5,717 kg/hr, generated from every
cargo tank, is changed into boil-off gas of about -120 degrees
centigrade, 0.05 bar, g, 6,127 kg/hr, is supplied to the boil-off
gas compressor 10, and is supplied to the cryogenic heat exchanger
20 after being compressed into boil-off gas of a predetermined
temperature and a predetermined pressure, i.e. about - (below zero)
27 degrees centigrade, 3.49 bar, g.
[0025] The supplied boil-off gas, as described above, requires a
specific quantity of refrigerant having a specific temperature for
the sub-cooled liquefaction of boil-off gas. The cryogenic heat
exchanger 20 performs heat exchange between boil-off gas compressed
at the predetermined pressure by the refrigerator system 40, which
serves as a refrigerator system for producing the required
refrigerant and includes compressors, coolers, and a
turbo-expander, and cold refrigerant generated from the
refrigerator system 40 to liquefy boil-off gas, and supplies
boil-off gas about -167 degrees centigrade, 3.19 bar, g, 6,127
kg/hr to the liquefied natural gas phase separator 30.
[0026] Meanwhile, the liquefied natural gas phase separator 30 is
connected to the gas combustion unit 80 for oxidizing flash gas
generated from the liquefied natural gas phase separator 30 to
maintain the predetermined pressure of the liquefied natural gas
phase separator 30 when flash gas is generated and pressure is
increased due to the abnormal operation of the liquefied natural
gas phase separator 30. When flash gas is generated and pressure is
increased due to the abnormal operation of the liquefied natural
gas phase separator 30, the liquefied natural gas phase separator
30 discharges flash gas, generated from the liquefied natural gas
phase separator 30 to the gas combustion unit 80 via the check
valve 50 for preventing reverse flow due to the abnormal pressure
increase generated by flash gas and the pressure control valve 60,
which are installed in the pipe connected to the gas combustion
unit 80, so that the gas combustion unit 80 maintains the
predetermined pressure of the liquefied natural gas phase separator
30 by oxidizing flash gas.
[0027] In addition to operations as described above, particularly,
the operating system of a liquefied natural gas ship for performing
sub-cooled liquefaction of boil-off gas for re-liquefaction
according to the first preferred embodiment of the present
invention includes the parallel pipe having the same structure as
the structure in which the check valve 50 and the pressure control
valve 60 are installed in the pipe between the liquefied natural
gas phase separator 30 and the check valve 50. The parallel pipe
includes the check valve 50' for preventing reverse flow generated
due to the abnormal pressure increase, and the pressure control
valve 60' for maintaining the predetermined pressure of the
liquefied natural gas phase separator 30 by adjusting the quantity
of boil-off gas generated by the boil-off gas compressor 10 such
that the liquefied natural gas phase separator 30, operated under
the sub-cooling condition, is stably operated. The end of the
parallel pipe is connected to the pipe between the boil-off gas
compressor 10 and the cryogenic heat exchanger 20 such that
boil-off gas, discharged from the boil-off gas compressor 10, is
supplied to the upper vapor region of the liquefied natural gas
phase separator 30 for the purpose of blanket during sub-cooling
liquefying operation. Thus, pressure and level of liquefied natural
gas of the liquefied natural gas phase separator 30 are stably
controlled.
[0028] The operating system of a liquefied natural gas ship for
performing sub-cooled liquefaction of boil-off gas for
re-liquefaction according to the second preferred embodiment of the
present invention will be described in detail with reference to
FIG. 2 as follows.
[0029] The operating system of a liquefied natural gas ship
according to the second preferred embodiment of the present
invention includes most of elements of the operating system of a
liquefied natural gas ship according to the first preferred
embodiment of the present invention, and particularly, further
includes a parallel pipe connected to a pipe for connecting the
liquefied natural gas phase separator 30 with the check valve 50 in
parallel and has the same structure as that of the pipe in which
the check valve 50 and the pressure control valve 60 are installed.
The parallel pipe is connected to a nitrogen generator 70 installed
in the machinery space of the liquefied natural gas ship and serves
to supply nitrogen gas to the liquefied natural gas phase separator
30, operated under the sub-cooling condition, for the purpose of
maintaining a predetermined pressure of the liquefied natural gas
phase separator 30. The parallel pipe includes the check valve 50'
for preventing reverse flow generated when pressure of the pipe is
abnormally increased and the pressure control valve 60' for
maintaining the predetermined pressure of the liquefied natural gas
phase separator 30 by adjusting the quantity of nitrogen gas for
the purpose of stable operation of the liquefied natural gas phase
separator 30 operated under the sub-cooling condition.
[0030] Operations of the operating system of a liquefied natural
gas ship for performing sub-cooled liquefaction of boil-off gas for
re-liquefaction according to the second preferred embodiment of the
present invention are identical to those of the operating system
according to the first preferred embodiment of the present
invention. The operating system according to the second preferred
embodiment of the present invention includes the parallel pipe
connected to the pipe for connecting the liquefied natural gas
phase separator 30 with the check valve 50 in parallel and has the
same structure as that of the pipe in which the check valve 50 and
the pressure control valve 60 are installed. The parallel pipe is
connected to the nitrogen generator 70 installed in the machinery
space of the liquefied natural gas ship and serves to supply
nitrogen gas to the liquefied natural gas phase separator 30,
operated under the sub-cooling condition, for the purpose of
maintaining a predetermined pressure of the liquefied natural gas
phase separator 30, and includes the check valve 50' for preventing
reverse flow generated when pressure of the pipe is abnormally
increased and a pressure control valve 60' for maintaining the
predetermined pressure of the liquefied natural gas phase separator
30 by adjusting the quantity of nitrogen gas for the purpose of
stable operation of the liquefied natural gas phase separator 30
operated under the sub-cooling condition. According to the
operating system according to the second preferred embodiment of
the present invention, power consumption caused by additional
boil-off gas and pressure loss, generated due to excess generation
of two-phase regions in a liquefied natural gas return line, is
effectively reduced and economical efficiency is achieved due to
simple operation. Moreover, due to the structure different from the
structure of the operation system according to the first preferred
embodiment of the present invention, nitrogen gas is supplied from
the nitrogen generator 70 to the vapor region of the liquefied
natural gas phase separator 30 for the purpose of blanket during
the sub-cooled liquefaction, so that operating pressure and level
of liquefied natural gas of the liquefied natural gas phase
separator 30 are stably controlled.
[0031] Although the preferred embodiment of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
[0032] As described above, a system of re-liquefying boil-off gas
in a liquefied natural gas ship is modified into an efficient
sub-cooled liquefaction system so that power consumption caused by
additional boil-off gas and pressure loss, generated due to excess
generation of two-phase regions in a liquefied natural gas return
line, is effectively reduced. Moreover, due to the structure
different from the structure of the operation system according to
the first preferred embodiment of the present invention, nitrogen
gas is supplied from the nitrogen generator to the vapor region of
the liquefied natural gas phase separator for the purpose of
blanket during the sub-cooled liquefaction, so that operating
pressure and level of liquefied natural gas of the liquefied
natural gas phase separator are stably controlled, and economical
efficiency is achieved due to simple operation.
* * * * *