U.S. patent application number 15/579578 was filed with the patent office on 2018-06-14 for ship.
This patent application is currently assigned to DAEWOO SHIPBUILDING & MARINE ENGINEERING CO., LTD.. The applicant listed for this patent is DAEWOO SHIPBUILDING & MARINE ENGINEERING CO., LTD.. Invention is credited to Su Kyung AN, Dong Kyu CHOI, Hyun Min JANG, Joon Chae LEE, Young Sik MOON, Hyun Jun SHIN, Jae Wook SON.
Application Number | 20180162492 15/579578 |
Document ID | / |
Family ID | 57440573 |
Filed Date | 2018-06-14 |
United States Patent
Application |
20180162492 |
Kind Code |
A1 |
AN; Su Kyung ; et
al. |
June 14, 2018 |
SHIP
Abstract
A ship includes: an boil-off gas heat exchanger installed on a
downstream of the storage tank such that compressed boil-off gas
("first fluid") is made to exchange heat and cooled using boil-off
gas discharged from the storage tank as a refrigerant; a compressor
installed on a downstream of the boil-off gas heat exchanger so as
to compress a part of the boil-off gas discharged from the storage
tank; an extra compressor installed on a downstream of the boil-off
gas heat exchanger in parallel with the compressor so as to
compress the other part of the boil-off gas discharged from the
storage tank; a refrigerant heat exchanger for additionally cooling
the first fluid that is cooled by the boil-off gas heat exchanger;
and a refrigerant decompressing device which expands the second
fluid sent to the refrigerant heat exchanger and cooled by the
refrigerant heat exchanger.
Inventors: |
AN; Su Kyung;
(Gwangmyeong-si, KR) ; CHOI; Dong Kyu;
(Seongnam-si, KR) ; MOON; Young Sik;
(Gwangmyeong-si, KR) ; SHIN; Hyun Jun; (Seoul,
KR) ; JANG; Hyun Min; (Seoul, KR) ; SON; Jae
Wook; (Seoul, KR) ; LEE; Joon Chae; (Seoul,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DAEWOO SHIPBUILDING & MARINE ENGINEERING CO., LTD. |
Seoul |
|
KR |
|
|
Assignee: |
DAEWOO SHIPBUILDING & MARINE
ENGINEERING CO., LTD.
Seoul
KR
|
Family ID: |
57440573 |
Appl. No.: |
15/579578 |
Filed: |
April 5, 2016 |
PCT Filed: |
April 5, 2016 |
PCT NO: |
PCT/KR2016/003545 |
371 Date: |
December 4, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02M 21/0287 20130101;
F17C 2221/033 20130101; F25J 1/0294 20130101; F25J 1/0277 20130101;
B63B 25/16 20130101; B63J 2099/003 20130101; B63H 21/38 20130101;
F17C 2265/066 20130101; F25J 1/0249 20130101; Y02T 10/30 20130101;
F25J 1/0288 20130101; F17C 2265/037 20130101; F25J 1/0025 20130101;
F17C 2223/0161 20130101; F25J 1/004 20130101; F17C 2227/0358
20130101; F25J 1/023 20130101; F25J 2290/72 20130101; F17C 9/02
20130101; F17C 2270/0105 20130101; F25J 1/0045 20130101; F17C
2265/03 20130101; F17C 2227/0339 20130101; F25J 1/0037 20130101;
F17C 6/00 20130101; F02M 21/0215 20130101; F25J 1/0202 20130101;
F17C 2223/033 20130101; Y02T 70/50 20130101; F17C 2227/0185
20130101 |
International
Class: |
B63B 25/16 20060101
B63B025/16; F25J 1/00 20060101 F25J001/00; F02M 21/02 20060101
F02M021/02; B63H 21/38 20060101 B63H021/38; F25J 1/02 20060101
F25J001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 2, 2015 |
KR |
10-2015-0078142 |
Sep 25, 2015 |
KR |
10-2015-0136257 |
Dec 10, 2015 |
KR |
10-2015-0176111 |
Claims
1. A ship including a storage tank storing liquefied gas,
comprising: an, boil-off gas heat exchanger installed on a
downstream of the storage tank such that compressed boil-off gas
(hereinafter, referred to as "first fluid") is made to exchange
heat and cooled using boil-off gas, which is discharged from the
storage tank, as a refrigerant; a compressor installed on a
downstream of the boil-off gas heat exchanger so as to compress a
part of the boil-off gas discharged from the storage tank; an extra
compressor installed on a downstream of the boil-off gas heat
exchanger in parallel with the compressor so as to compress the
other part of the boil-off gas discharged from the storage tank; a
refrigerant heat exchanger for additionally cooling the first fluid
that is cooled by the boil-off gas heat exchanger; a refrigerant
decompressing device which expands the second fluid, which is sent
to the refrigerant heat exchanger (hereinafter, referred to as
"second fluid") and cooled by the refrigerant heat exchanger, and
then sends the second fluid back to the refrigerant heat exchanger;
a first decompressing device which expands a part of the first
fluid, which is cooled by the boil-off gas heat exchanger and by
the refrigerant heat exchanger; and a third decompressing device
which expands the remaining part of the first fluid, which is
cooled by the boil-off gas heat exchanger and by the refrigerant
heat exchanger, and sends the expanded remaining part of the first
fluid back to the refrigerant heat exchanger, wherein the
refrigerant heat exchanger heat-exchanges the first fluid to cool
the first fluid, using the second fluid, a fluid expanded by the
refrigerant decompressing device, and a fluid decompressed by the
third decompressing device as a refrigerant; the first fluid is
boil-off gas compressed by the compressor or is a confluent flow of
the boil-off gas compressed by the compressor and the boil-off gas
compressed by the extra compressor; and the second fluid is the
boil-off gas compressed by the extra compressor or a confluent flow
of the boil-off gas compressed by the compressor and the boil-off
gas compressed by the extra compressor.
2. The ship of claim 1, further comprising: a gas-liquid separator
that separates the partially re-liquefied liquefied gas passing
through the boil-off gas heat exchanger, the refrigerant heat
exchanger, and the first decompressing device and the boil-off gas
remaining in a gas phase, in which the liquefied gas separated by
the gas-liquid separator is sent to the storage tank, and the
boil-off gas separated by the gas-liquid separator is sent to the
boil-off gas heat exchanger.
3. The ship of claim 1, wherein the first fluid is branched into
two flows on an upstream of a high pressure engine, and a part of
the first fluid is sent to the boil-off gas heat exchanger to be
cooled and the other part thereof is sent to the high pressure
engine.
4. The ship of claim 1, wherein the fluid passing through the third
decompressing device and the refrigerant heat exchanger is sent to
a low pressure engine.
5. The ship of claim 1, wherein the second fluid which is
compressed by the extra compressor, passes through the refrigerant
heat exchanger and the refrigerant decompressing device, and then
used as the refrigerant in the refrigerant heat exchanger is sent
back to the extra compressor to form a refrigerant cycle of a
closed loop in which the extra compressor, the refrigerant heat
exchanger, the refrigerant decompressing device, and the
refrigerant heat exchanger are connected.
6. The ship of claim 1, wherein the second fluid which is
compressed by the extra compressor, passes through the refrigerant
heat exchanger and the refrigerant decompressing device, and then
used as the refrigerant in the refrigerant heat exchanger is
discharged from the storage tank and then joined with the boil-off
gas passing the boil-off gas heat exchanger.
7. The ship of claim 1, further comprising: a valve which is
installed on a line connecting the boil-off gas compressed by the
compressor with the boil-off gas compressed by the extra
compressor, in which the valve is open and closed to join the
boil-off gas compressed by the compressor with the boil-off gas
compressed by the extra compressor or separate the boil-off gas
compressed by the compressor from the boil-off gas compressed by
the extra compressor.
8. The ship of claim 1, wherein the refrigerant decompressing
device is an expander, and the fluid just before passing through
the refrigerant decompressing device and the fluid just after
passing through the refrigerant decompressing device are a gas
phase.
9. A boil-off gas treatment system for a ship including a storage
tank for storing a liquefied gas, comprising: a first supply line
along which boil-off gas, which is discharged from the storage tank
and partially compressed by a compressor, is sent to a high
pressure engine; a second supply line which is branched from the
first supply line and has an extra compressor provided thereon,
with the extra compressor compressing the other part of the
boil-off gas discharged from the storage tank; a return line which
is branched from the first supply line and has a boil-off gas heat
exchanger, a refrigerant heat exchanger, and a first decompressing
device provided thereon, with the compressed boil-off gas being
re-liquefied by passing through the boil-off gas heat exchanger,
the refrigerant heat exchanger, and the first decompressing device;
a recirculation line which has the refrigerant heat exchanger and a
refrigerant decompressing device provided thereon, with the
boil-off gas, which is cooled by passing through the refrigerant
heat exchanger and a refrigerant decompressing device, being sent
back to the refrigerant heat exchanger to be used as a refrigerant
and then joined with the boil-off gas discharged from the storage
tank; a first additional line which connects between the
recirculation line on a downstream of the refrigerant decompressing
device and the refrigerant heat exchanger and a second supply line
on an upstream of the extra compressor; and a third supply line
which is branched from the return line on the downstream of the
refrigerant heat exchanger, the boil-off gas being sent to the low
pressure engine by passing through a third decompressing device and
the refrigerant heat exchanger; wherein the boil-off gas heat
exchanger heat-exchanges and cools the boil-off gas supplied along
the return line by the boil-off gas discharged from the storage
tank as the refrigerant, and the refrigerant heat exchanger
heat-exchanges and cools the boil-off gas supplied along the return
line by the boil-off gas supplied along the recirculation line, the
fluid passing through the refrigerant decompressing device, and the
fluid supplied along the third supply line as the refrigerant.
10. The boil-off gas treatment system of claim 9, further
comprising: a first valve which is installed on the upstream of the
compressor on the first supply line; a second valve which is
installed on the downstream of the compressor on the first supply
line; a third valve which is installed on, the upstream of the
extra compressor on the second supply line; a fourth valve
installed on the downstream of the extra compressor on the second
supply line; a sixth valve which is provided between the first
supply line and the second supply line on the recirculation line
along which the boil-off gas branched from the first supply line is
sent to the refrigerant heat exchanger; a ninth valve which is
installed on the recirculation line for sending the boil-off gas
from the refrigerant heat exchanger to the first supply line; a
tenth valve which is installed on the first additional line; and a
twelfth valve which is installed on the recirculation line between
the second supply line and the refrigerant heat exchanger.
11. The boil-off gas treatment system of claim 10, wherein the
system is operated while the first valve, the second valve, the
third valve, the fourth valve, the tenth valve, and the twelfth
valve are open and the sixth valve and the ninth valve are closed,
and if the boil-off gas is supplied to the extra compressor, the
third valve is closed to form the refrigerant cycle of the closed
loop in which the boil-off gas circulates the extra compressor, the
fourth valve, the twelfth valve, the refrigerant heat exchanger,
the refrigerant decompressing device, the refrigerant heat
exchanger, and the tenth valve.
12. The boil-off gas treatment system of claim 11, wherein if the
compressor fails, the first valve, the second valve, the tenth
valve, and the twelfth valve are closed and the third valve and the
sixth valve are open to supply the boil-off gas, which is
discharged from the storage tank and then passes through the
boil-off gas heat exchanger, to the high pressure engine via the
third valve, the extra compressor, the fourth valve, and the sixth
valve.
13. The boil-off gas treatment system of claim 10, wherein the
first valve, the second valve, the third valve, the fourth valve,
the sixth valve, the ninth valve, an the twelfth valve are open and
the tenth valve is closed so that the boil-off gas compressed by
the compressor and the boil-off gas compressed by the extra
compressor are joined and operated.
14. The boil-off gas treatment system of claim 13, wherein if the
compressor fails, the first valve, the second valve, the ninth
valve, and the twelfth valve are closed to supply the boil-off gas,
which is discharged from the storage tank and then passes through
the boil-off gas heat exchanger, to the high pressure engine via
the third valve, the extra compressor, the fourth valve, and the
sixth valve.
15. The boil-off gas treatment system of claim 10, wherein the
first valve, the second valve, the third valve, the fourth valve,
the ninth valve, and the twelfth valve are open and the sixth valve
and the tenth valve are closed so that the boil-off gas compressed
by the compressor and the boil-off gas compressed by the extra
compressor are separated and operated.
16. The boil-off gas treatment system of claim 15 wherein if the
compressor fails, the first valve, the second valve, the ninth
valve, and the twelfth valve are closed and the sixth valve is open
to supply the boil-off gas, which is discharged from the storage
tank and then passes through the boil-off gas heat exchanger, to
the high pressure engine via the third valve, the extra compressor,
the fourth valve, and the sixth valve.
17. A method, comprising: 1) branching boil-off gas discharged from
a liquefied gas storage tank into two and compressing one flow of
the branched boil-off gas by a compressor; compressing the other
flow by an extra compressor; 2) sending at least one of the
boil-off gas compressed by the compressor and the boil-off gas
compressed by the extra compressor to a high pressure engine or
re-liquefying the boil-off gas to return the boil-off gas to the
storage tank (hereinafter, referred to as `returning boil-off gas`)
re-circulate the boil-off gas (hereinafter, referred to as
`re-circulated boil-off gas`); 3) heat-exchanging and cooling the
`returning boil-off gas` by the boil-off gas discharged from the
storage tank as a refrigerant and then heat-exchanging the cooled
returning boil-off gas' with the `re-circulated boil-off gas` and
the `decompressed boil-off gas` to be additionally cooled, and 4)
the `recirculation boil-off gas` is cooled and expanded to exchange
heat with the `returning boil-off gas` and `decompressed boil-off
gas`, and the `decompressed boil-off gas` is a fluid decompressed
by branching a part of the `returning boil-off gas` cooled and
additionally cooled in the step 3).
18. The method of claim 17, wherein in the step 3), the `returning
boil-off gas` is cooled by exchanging heat with the boil-off gas
discharged from the storage tank as the refrigerant, and then
additionally cooled by exchanging heat with the `re-circulated
boil-off gas` before being cooled and expanded, the cooled and
expanded `re-circulated boil-off gas`, and the `decompressed
boil-off gas`, and in the step 4), the `re-circulated boil-off gas`
before being cooled and expanded exchanges heat with the cooled and
expanded `re-circulated boil-off gas`, the `returning boil-off
gas`, and the `decompressed boil-off gas` to be cooled and then
expanded.
19. The method of claim 17, wherein the `decompressed boil-off gas`
used as the refrigerant for the heat exchange is sent to the low
pressure engine.
20. The method of claim 17, wherein the downstream line of the
compressor and the downstream line of the extra compressor are
connected to each other to join the boil-off gas compressed by the
compressor with the boil-off gas compressed by the extra
compressor.
Description
TECHNICAL FIELD
[0001] The present invention relates to a ship, and more
particularly, to a ship including a system for re-liquefying
boil-off gas left after being used as fuel of an engine among
boil-off gases generated in a storage tank.
BACKGROUND ART
[0002] In recent years, consumption of liquefied gas such as
liquefied natural gas (LNG) has been rapidly increasing worldwide.
Since a volume of liquefied gas obtained by liquefying gas at a low
temperature is much smaller than that of gas, the liquefied gas has
an advantage of being able to increase storage and transport
efficiency. In addition, the liquefied gas, including liquefied
natural gas, can remove or reduce air pollutants during the
liquefaction process, and therefore may also be considered as
eco-friendly fuel with less emission of air pollutants during
combustion.
[0003] The liquefied natural gas is a colorless transparent liquid
obtained by cooling and liquefying methane-based natural gas to
about -162.degree. C., and has about 1/600 less volume than that of
natural gas. Therefore, to very efficiently transport the natural
gas, the natural gas needs to be liquefied and transported.
[0004] However, since the liquefaction temperature of the natural
gas is a cryogenic temperature of -162.degree. C. at normal
pressure, the liquefied natural gas is sensitive to temperature
change and easily boiled-off. As a result, the storage tank storing
the liquefied natural gas is subjected to a heat insulating
process. However, since external heat is continuously sent to the
storage tank, boil-off gas (BOG) is generated as the liquefied
natural gas is continuously vaporized naturally in the storage tank
during transportation of the liquefied natural gas. This goes the
same for other low-temperature liquefied gases such as ethane.
[0005] The boil-off gas is a kind of loss and is an important
problem in transportation efficiency. In addition, if the boil-off
gas is accumulated in the storage tank, an internal pressure of the
tank may rise excessively, and if the internal pressure of the tank
becomes more severe, the tank is highly likely to be damaged.
Accordingly, various methods for treating the boil-off gas
generated in the storage tank have been studied. Recently, to treat
the boil-off gas, a method for re-liquefying boil-off gas and
returning the re-liquefied boil-off gas to the storage tank, a
method for using boil-off gas as an energy source for fuel
consumption places like an engine of a ship, or the like have been
used.
[0006] As the method for re-liquefying boil-off gas, there are a
method for re-liquefying boil-off gas by heat-exchanging the
boil-off gas with a refrigerant by a refrigeration cycle using a
separate refrigerant, a method for re-liquefying boil-off gas by
the boil-off gas itself as a refrigerant without using a separate
refrigerant, or the like. In particular, the system employing the
latter method is called a partial re-liquefaction System (PRS).
[0007] Generally, on the other hand, as engines which can use
natural gas as fuel among engines used for a ship, there are gas
fuel engines such as a DFDE engine and an ME-GI engine.
[0008] The DFDE engine adopts an Otto cycle which consists of four
strokes and injects natural gas with a relatively low pressure of
approximately 6.5 bars into a combustion air inlet and compresses
the natural gas as the piston lifts up.
[0009] The ME-GI engine adopts a diesel cycle which consists of two
strokes and employs a diesel cycle which directly injects high
pressure natural gas near 300 bars into the combustion chamber
around a top dead point of the piston. Recently, there is a growing
interest in the ME-GI engine, which has better fuel efficiency and
boost efficiency.
DISCLOSURE
Technical Problem
[0010] An object of the present invention is to provide a ship
including a system capable of providing better boil-off gas
re-liquefying performance than the existing partial re-liquefaction
system.
Technical Solution
[0011] A ship including a storage tank storing liquefied gas,
includes: an boil-off gas heat exchanger installed on a downstream
of the storage tank such that compressed boil-off gas (hereinafter,
referred to as "first fluid") is made to exchange heat and cooled
using boil-off gas, which is discharged from the storage tank, as a
refrigerant; a compressor installed on a downstream of the boil-off
gas heat exchanger so as to compress a part of the boil-off gas
discharged from the storage tank; an extra compressor installed on
a downstream of the boil-off gas heat exchanger in parallel with
the compressor so as to compress the other part of the boil-off gas
discharged from the storage tank; a refrigerant heat exchanger for
additionally cooling the first fluid that is cooled by the boil-off
gas heat exchanger; a refrigerant decompressing device which
expands the second fluid, which is sent to the refrigerant heat
exchanger (hereinafter, referred to as "second fluid") and cooled
by the refrigerant heat exchanger, and then sends the second fluid
back to the refrigerant heat exchanger; a first decompressing
device which expands a part of the first fluid, which is cooled by
the boil-off gas heat exchanger and by the refrigerant heat
exchanger; and a third decompressing device which expands the
remaining part of the first fluid, which is cooled by the boil-off
gas heat exchanger and by the refrigerant heat exchanger, and sends
the expanded remaining part of the first fluid back to the
refrigerant heat exchanger, wherein the refrigerant heat exchanger
heat-exchanges the first fluid to cool the first fluid, using the
second fluid, a fluid expanded by the refrigerant decompressing
device, and a fluid decompressed by the third decompressing device
as a refrigerant; the first fluid is boil-off gas compressed by the
compressor or is a confluent flow of the boil-off gas compressed by
the compressor and the boil-off gas compressed by the extra
compressor; and the second fluid is the boil-off gas compressed by
the extra compressor or a confluent flow of the boil-off gas
compressed by the compressor and the boil-off gas compressed by the
extra compressor.
[0012] The ship may further include a gas-liquid separator that
separates the partially re-liquefied liquefied gas passing through
the boil-off gas heat exchanger, the refrigerant heat exchanger,
and the first decompressing device and the boil-off gas remaining
in a gas phase, in which the liquefied gas separated by the
gas-liquid separator may be sent to the storage tank, and the
boil-off gas separated by the gas-liquid separator may be sent to
the boil-off gas heat exchanger.
[0013] The first fluid may be branched into two flows on an
upstream of a high pressure engine, and a part of the first fluid
may be sent to the boil-off gas heat exchanger to be cooled and the
other part thereof may be sent to the high pressure engine.
[0014] The fluid passing through the third decompressing device and
the refrigerant heat exchanger may be sent to a low pressure
engine.
[0015] The second fluid which is compressed by the extra
compressor, passes through the refrigerant heat exchanger and the
refrigerant decompressing device, and then used as the refrigerant
in the refrigerant heat exchanger may be sent back to the extra
compressor to form a refrigerant cycle of a closed loop in which
the extra compressor, the refrigerant heat exchanger, the
refrigerant decompressing device, and the refrigerant heat
exchanger are connected.
[0016] The second fluid which is compressed by the extra
compressor, passes through the refrigerant heat exchanger and the
refrigerant decompressing device, and then used as the refrigerant
in the refrigerant heat exchanger may be discharged from the
storage tank and then joined with the boil-off gas passing the
boil-off gas heat exchanger.
[0017] The ship may further include a valve which is installed on a
line connecting the boil-off gas compressed by the compressor with
the boil-off gas compressed by the extra compressor, in which the
valve may be opened and closed to join the boil-off gas compressed
by the compressor with the boil-off gas compressed by the extra
compressor or separate the boil-off gas compressed by the
compressor from the boil-off gas compressed by the extra
compressor.
[0018] The refrigerant decompressing device may be an expander, and
the fluid just before passing through the refrigerant decompressing
device and the fluid just after passing through the refrigerant
decompressing device may be a gas phase.
[0019] A boil-off gas treatment system for a ship including a
storage tank for storing a liquefied gas, includes: a first supply
line along which boil-off gas, which is discharged from the storage
tank and partially compressed by a compressor, is sent to a high
pressure engine; a second supply line which is branched from the
first supply line and has an extra compressor provided thereon,
with the extra compressor compressing the other part of the
boil-off gas discharged from the storage tank; a return line which
is branched from the first supply line and has a boil-off gas heat
exchanger, a refrigerant heat exchanger, and a first decompressing
device provided thereon, with the compressed boil-off gas being
re-liquefied by passing through the boil-off gas heat exchanger,
the refrigerant heat exchanger, and the first decompressing device;
a recirculation line which has the refrigerant heat exchanger and a
refrigerant decompressing device provided thereon, with the
boil-off gas, which is cooled by passing through the refrigerant
heat exchanger and a refrigerant decompressing device, being sent
back to the refrigerant heat exchanger to be used as a refrigerant
and then joined with the boil-off gas discharged from the storage
tank; a first additional line which connects between the
recirculation line on a downstream of the refrigerant decompressing
device and the refrigerant heat exchanger and a second supply line
on an upstream of the extra compressor; and a third supply line
which is branched from the return line on the downstream of the
boil-off gas heat exchanger, the boil-off gas being sent to the low
pressure engine by passing through a third decompressing device and
the refrigerant heat exchanger; wherein the boil-off gas heat
exchanger heat-exchanges the boil-off gas supplied along the return
line by the boil-off gas discharged from the storage tank as the
refrigerant, the refrigerant heat exchanger heat-exchanges the
boil-off gas supplied along the return line by the boil-off gas
supplied along the recirculation line, the fluid passing through
the refrigerant decompressing device, and the fluid supplied along
the third supply line to be cooled.
[0020] The boil-off gas treatment system for a ship may further
include: a first valve which is installed on the upstream of the
compressor on the first supply line; a second valve which is
installed on the downstream of the compressor on the first supply
line; a third valve which is installed on the upstream of the extra
compressor on the second supply line; a fourth valve installed on
the downstream of the extra compressor on the second supply line; a
sixth valve which is provided between the first supply line and the
second supply line on the recirculation line along which the
boil-off gas branched from the first supply line is sent to the
refrigerant heat exchanger; a ninth valve which is installed on the
recirculation line for sending the boil-off gas from the
refrigerant heat exchanger to the first supply line; a tenth valve
which is installed on the first additional line; and a twelfth
valve which is installed on the recirculation line between the
second supply line and the refrigerant heat exchanger.
[0021] The system may be operated while the first valve, the second
valve, the third valve, the fourth valve, the tenth valve, and the
twelfth valve are open and the sixth valve and the ninth valve are
closed, and if the boil-off gas is supplied to the extra
compressor, the third valve may be closed to form the refrigerant
cycle of the closed loop in which the boil-off gas circulates the
extra compressor, the fourth valve, the twelfth valve, the
refrigerant heat exchanger, the refrigerant decompressing device,
the refrigerant heat exchanger, and the tenth valve.
[0022] If the compressor fails, the first valve, the second valve,
the tenth valve, and the twelfth valve may be closed and the third
valve and the sixth valve may be open to supply the boil-off gas,
which is discharged from the storage tank and then passes through
the boil-off gas heat exchanger, to the high pressure engine via
the third valve, the extra compressor, the fourth valve, and the
sixth valve.
[0023] The first valve, the second valve, the third valve, the
fourth valve, the sixth valve, the ninth valve, an the twelfth
valve may be open and the tenth valve may be closed so that the
boil-off gas compressed by the compressor and the boil-off gas
compressed by the extra compressor may be joined and operated.
[0024] If the compressor fails, the first valve, the second valve,
the ninth valve, and the twelfth valve may be closed to supply the
boil-off gas, which is discharged from the storage tank and then
passes through the boil-off gas heat exchanger, to the high
pressure engine via the third valve, the extra compressor, the
fourth valve, and the sixth valve.
[0025] The first valve, the second valve, the third valve, the
fourth valve, the ninth valve, and the twelfth valve may be open
and the sixth valve and the tenth valve may be closed so that the
boil-off gas compressed by the compressor and the boil-off gas
compressed by the extra compressor may be separated and
operated.
[0026] If the compressor fails, the first valve, the second valve,
the ninth valve, and the twelfth valve may be closed and the sixth
valve may be open to supply the boil-off gas, which is discharged
from the storage tank and then passes through the boil-off gas heat
exchanger, to the high pressure engine via the third valve, the
extra compressor, the fourth valve, and the sixth valve.
[0027] A method includes: 1) branching boil-off gas discharged from
a liquefied gas storage tank into two and compressing one flow of
the branched boil-off gas by a compressor; compressing the other
flow by an extra compressor; 2) sending at least one of the
boil-off gas compressed by the compressor and the boil-off gas
compressed by the extra compressor to a high pressure engine or
re-liquefying the boil-off gas to return the boil-off gas to the
storage tank (hereinafter, referred to as `returning boil-off gas`)
or re-circulate the boil-off gas (hereinafter, referred to as
`re-circulated boil-off gas`), 3) heat-exchanging and cooling the
`returning boil-off gas` by the boil-off gas discharged from the
storage tank as a refrigerant and then heat-exchanging the cooled
returning boil-off gas' with the `re-circulated boil-off gas` and
the `decompressed boil-off gas` to be additionally cooled; and 4)
cooling and expanding the `recirculation boil-off gas` and
heat-exchanging the cooled and expanded recirculation boil-off gas
with the `returning boil-off gas` and the `decompressed boil-off
gas`, wherein the `decompressed boil-off gas` is a fluid
decompressed by branching a part of the `returning boil-off gas`
cooled and additionally cooled in the step 3).
[0028] In the step 3), the `returning boil-off gas` may be cooled
by exchanging heat with the boil-off gas discharged from the
storage tank as the refrigerant, and then may be additionally
cooled by exchanging heat with the `re-circulated boil-off gas`
before being cooled and expanded, the cooled and expanded
`re-circulated boil-off gas`, and the `decompressed boil-off gas`,
and in the step 4), the `recirculation boil-off gas` before being
cooled and expanded may exchange heat with the cooled and expanded
`recirculation boil-off gas`, the `returning boil-off gas`, and the
`decompressed boil-off gas` to be cooled and then expanded.
[0029] The `decompressed boil-off gas` used as the refrigerant for
the heat exchange may be sent to the low pressure engine.
[0030] The downstream line of the compressor and the downstream
line of the extra compressor may be connected to each other to join
the boil-off gas compressed by the compressor with the boil-off gas
compressed by the extra compressor.
Advantageous Effects
[0031] Compared with the existing partial re-liquefaction system
(PRS), the present invention can increase the re-liquefaction
efficiency and the re-liquefaction amount since the boil-off gas is
decompressed after undergoing the additional cooling process by the
refrigerant heat exchanger. In particular, most or all of the
remaining boil-off gas can be re-liquefied without employing the
refrigeration cycle using the separate refrigerant, and therefore
increasing the economical efficiency.
[0032] Further, according to the present invention, it is possible
to flexibly control the refrigerant flow rate and the supply of
cold heat in response to the discharge amount of the boil-off gas,
the engine load depending on the operating speed of the ship, and
the like.
[0033] According to the embodiment of the present invention, it is
possible to contribute to securing the space on the ship and save
the cost of additionally installing the compressor by increasing
the re-liquefaction efficiency and the re-liquefaction amount by
using the extra compressor already provided. In particular, the
refrigerant heat exchanger can use not only the boil-off gas
compressed by the extra compressor but also the boil-off gas
compressed by the compressor as the refrigerant to increase the
flow rate of the boil-off gas used as the refrigerant in the
refrigerant heat exchanger, thereby more increasing the
re-liquefaction efficiency and the re-liquefaction amount.
[0034] According to another embodiment of the present invention,
the decompressed boil-off gas sent to the low pressure engine can
be used as the refrigerant in the refrigerant heat exchanger,
thereby increasing the re-liquefaction efficiency and the
re-liquefaction amount.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIG. 1 is a configuration diagram schematically showing the
existing partial re-liquefaction system.
[0036] FIG. 2 is a configuration diagram schematically showing a
boil-off gas treatment system for a ship according to a first
embodiment of the present invention.
[0037] FIG. 3 is a configuration diagram schematically showing a
boil-off gas treatment system for a ship according to a second
embodiment of the present invention.
[0038] FIG. 4 is a configuration diagram schematically showing a
boil-off gas treatment system for a ship according to a third
embodiment of the present invention.
[0039] FIG. 5 is a configuration diagram schematically showing a
boil-off gas treatment system for a ship according to a fourth
embodiment of the present invention.
[0040] FIG. 6 is a graph schematically illustrating a phase change
of methane depending on temperature and pressure.
BEST MODE
[0041] Hereinafter, configurations and effects of exemplary
embodiments of the present invention will be described with
reference to the accompanying drawings. The present invention can
variously be applied to ships such as a ship equipped with an
engine using natural gas as fuel and a ship including a liquefied
gas storage tank. In addition, the following embodiments may be
changed in various forms, and therefore the technical scope of the
present invention is not limited to the following embodiments.
[0042] Boil-off gas systems of the present invention to be
described below can be applied to offshore structures such as LNG
FPSO and LNG FSRU, in addition to all types of ships and offshore
structures equipped with a storage tank capable of storing a
low-temperature fluid cargo or liquefied gas, i.e., ships such as a
liquefied natural gas carrier, a liquefied ethane gas carrier, and
LNG RV. However, for convenience of explanation, the following
embodiments will describe, by way of example, liquefied natural gas
which is a typical low-temperature fluid cargo.
[0043] Further, a fluid on each line of the present invention may
be in any one of a liquid phase, a gas-liquid mixed state, a gas
phase, and a supercritical fluid state, depending on operating
conditions of a system.
[0044] FIG. 1 is a configuration diagram schematically showing the
existing partial re-liquefaction system.
[0045] Referring to FIG. 1, in the conventional partial
re-liquefaction system, the boil-off gas generated and discharged
from a storage tank storing a fluid cargo is sent along a pipe and
compressed by a boil-off gas compressor 10.
[0046] A storage tank T is provided with a sealing and heat
insulating barrier to be able to store liquefied gas such as
liquefied natural gas at a cryogenic temperature. However, the
sealing and heat insulating barrier may not completely shut off
heat transmitted from the outside. Therefore, the liquefied gas is
continuously evaporated in the storage tank, so an internal
pressure of the storage tank may be increased. Accordingly, to
prevent the pressure of the tank from excessively increasing due to
the boil-off gas and keep the internal pressure of the tank at an
appropriate level, the boil-off gas in the storage tank is
discharged and is then supplied to the boil-off compressor 10.
[0047] When the boil-off gas discharged from the storage tank and
compressed by the boil-off gas compressor 10 is referred to as a
first stream, the first flow of the compressed boil-off gas is
divided into a second flow and a third stream, and the second flow
may be formed to be liquefied and then return to the storage tank
T, and the third flow may be formed to be supplied to gas fuel
consumption places such as a boost engine and a power generation
engine in a ship. In this case, in the boil-off gas compressor 10
can compress the boil-off gas to a supply pressure of the fuel
consumption place, and the second flow may be branched via all or a
part of the boil-off gas compressor if necessary. All of the
boil-off gas compressed as the third flow may also be supplied
according to the amount of fuel required for the fuel consumption
place, and all of the compressed boil-off gas may return to the
storage tank by supplying the whole amount of boil-off gas as the
second stream. An example of the gas fuel consumption places may
include a DF generator, a gas turbine, DFDE, and the like, in
addition to high pressure gas injection engine (e.g., ME-GI engines
developed by MDT Co., etc.) and low-temperature gas injection
engines (e.g., generation X-dual fuel engine (X-DF engine) by
Wartsila Co.).
[0048] At this time, a heat exchanger 20 is provided to liquefy the
second flow of the compressed boil-off gas. The boil-off gas
generated from the storage tank is used as a cold heat supply
source of the compressed boil-off gas. The compressed boil-off gas,
that is, the second stream, whose temperature rises while being
compressed by the boil-off gas compressor while passing through the
heat exchanger 20 is cooled, and the boil-off gas generated from
the storage tank and introduced into the heat exchanger 20 is
heated and then supplied to the boil-off gas compressor 10.
[0049] Since a flow rate of pre-compressed boil-off gas is
compressed is greater than that of the second stream, the second
flow of the compressed boil-off gas may be at least partially
liquefied by receiving cold heat from the boil-off gas before being
compressed. As described above, the heat exchanger exchanges heat
the low-temperature boil-off gas immediately after being discharged
from the storage tank with the high-pressure boil-off gas
compressed by the boil-off gas compressor to liquefy the
high-pressure boil-off gas.
[0050] The boil-off gas of the second flow passing through the heat
exchanger 20 is further cooled while being decompressed by passing
through an expansion means 30 such as an expansion valve or an
expander and is then supplied to a gas-liquid separator 40. The
gas-liquid separator 40 separates the liquefied boil-off gas into
gas and liquid components. The liquid component, that is, the
liquefied natural gas returns to the storage tank, and the gas
component, that is, the boil-off gas is discharged from the storage
tank to be joined with a flow of boil-off gas supplied to the heat
exchanger 20 and the boil-off gas compressor 10 or is then supplied
back to the heat exchanger 20 to be utilized as a cold heat supply
source which heat-exchanges high-pressure boil-off gas compressed
by the boil-off gas compressor 10. Of course, the boil-off gas may
be sent to a gas combustion unit (GCU) or the like to be combusted
or may be sent to a gas consumption place (including a gas engine)
to be consumed. Another expansion means 50 for additionally
decompressing the gas separated by the gas-liquid separator before
being joined with the flow of boil-off gas may be further
provided.
[0051] FIG. 2 is a configuration diagram schematically showing a
boil-off gas treatment system for a ship according to a first
embodiment of the present invention.
[0052] Referring to FIG. 2, the system of the present embodiment
includes a refrigerant circulator 300a which is supplied with
boil-off gas generated from a low temperature fluid cargo stored in
a storage tank and circulates the boil-off gas as a
refrigerant.
[0053] To this end, the system includes a refrigerant supply line
CSLa which supplies boil-off gas from the storage tank to a
refrigerant circulator 300a. The refrigerant supply line is
provided with a valve 400a to shut off the refrigerant supply line
CSLa if a sufficient amount of boil-off gas, which may circulate
the refrigerant circulator, is supplied, such that the refrigerant
circulator 300a is operated as a closed loop.
[0054] Similar to the above-described basic embodiment, even in the
first modified embodiment, the compressor 100a for compressing the
boil-off gas generated from the low-temperature fluid cargo in the
storage tank T is also provided. The boil-off gas generated from
the storage tank is introduced into the compressor 100a along a
boil-off gas supply line BLa.
[0055] The storage tank (T) of the present embodiment may be an
independent type tank in which a load of the fluid cargo is not
directly applied to a heat insulating layer, or a membrane type
tank in which the load of the cargo is directly applied to the heat
insulating layer. The independent type tank can be used as a
pressure vessel which is designed to withstand a pressure of 2 barg
or more.
[0056] Meanwhile, in the present embodiment, only a line for
re-liquefying the boil-off gas is shown. However, the boil-off gas
compressed by the compressor may be supplied as fuel to a fuel
consumption place including a boost engine and a power generation
engine of a ship or an offshore structure. When a ship is anchored,
there is little or no consumption of gas fuel, the whole amount of
boil-off gas may also be supplied to a re-liquefaction line
RLa.
[0057] The compressed boil-off gas is supplied to a boil-off gas
heat exchanger 200a along the boil-off gas re-liquefaction line
RLa. The boil-off gas heat exchanger 200a is provided over the
boil-off gas re-liquefaction line RLa and the boil-off gas supply
line BLa to exchange heat between boil-off gas introduced into the
compressor 100a and the boil-off gas compressed by at least a part
of the compressor. The boil-off gas whose temperature rises during
the compression is cooled through the heat exchange with the
low-temperature boil-off gas which is generated from the storage
tank and is to be introduced into the compressor 100a.
[0058] A downstream of the boil-off gas heat exchanger 200a is
provided with a refrigerant heat exchanger 500a. The boil-off gas,
which is compressed and then heat-exchanged by the boil-off gas
heat exchanger is additionally cooled by the heat exchange with the
boil-off gas which circulates the refrigerant circulator 300a.
[0059] The refrigerant circulator 300a includes a refrigerant
compressor 310a which compresses the boil-off gas supplied from the
storage tank, a cooler 320a which cools the boil-off gas compressed
by the refrigerant compressor, and a refrigerant decompressing
device 330a which decompresses and additionally cools the boil-off
gas cooled by the cooler. The refrigerant decompressing device 330a
may be an expansion valve or an expander which adiabatically
expands and cools the boil-off gas.
[0060] The boil-off gas cooled by the refrigerant decompressing
device 330a is supplied as a refrigerant to the refrigerant heat
exchanger 500a along the refrigerant circulation line CCLa. The
refrigerant heat exchanger 500a cools the boil-off gas by the heat
exchange with the boil-off gas supplied via the boil-off gas heat
exchanger 200a. The boil-off gas of the refrigerant circulation
line CCLa passing through the refrigerant heat exchanger 500a is
circulated to the refrigerant compressor 310a and circulates the
refrigerant circulation line while undergoing the above-described
compression and cooling processes.
[0061] Meanwhile, the boil-off gas of the boil-off gas
re-liquefaction line RLa cooled by the refrigerant heat exchanger
500a is decompressed by a first decompressing device 600a. The
first decompressing device 600a may be an expansion valve, such as
a Joule-Thomson valve, or an expander.
[0062] The decompressed boil-off gas is separated into gas and
liquid by being supplied to a gas-liquid separator 700a on a
downstream of the first decompressing device 600a, and the liquid
separated by the gas-liquid separator 700a, that is, the liquefied
natural gas is supplied to the storage tank T and again stored.
[0063] The gas separated by the gas-liquid separator 700a, that is,
the boil-off gas is additionally decompressed by a second
decompressing device 800a, and is joined with the flow of boil-off
gas to be introduced into the boil-off gas heat exchanger 200a from
the storage tank T or is supplied to the boil-off gas heat
exchanger 200a to be utilized as the cold heat supply source which
heat-exchanges a high-pressure boil-off gas compressed by the
compressor 100a. Of course, the boil-off gas may be sent to a gas
combustion unit (GCU) or the like to be combusted or may be sent to
a fuel consumption place (including a gas engine) to be
consumed.
[0064] FIG. 3 is a configuration diagram schematically showing a
boil-off gas treatment system for a ship according to a second
embodiment of the present invention.
[0065] Referring to FIG. 3, according to the present embodiment, in
a refrigerant circulator 300b, the boil-off gas which is to be
introduced into a refrigerant decompressing device 330b from a
cooler 320b is cooled by exchanging heat with the boil-off gas
decompressed by the refrigerant decompressing device 330b and then
supplied to the refrigerant decompressing device 330b.
[0066] Since the boil-off gas is cooled while being decompressed by
the refrigerant decompressing device 330b, the boil-off gas
downstream of the refrigerant decompressing device has temperature
lower than that of the boil-off gas upstream of the refrigerant
decompressing device. In this regard, according to the present
embodiment, the boil-off gas upstream of the refrigerant
decompressing device is cooled by exchanging heat with the boil-off
gas downstream of the refrigerant decompressing device and then
introduced into the decompressing device. To this end, as
illustrated in FIG. 3, the boil-off gas upstream of the refrigerant
decompressing device 330b may be supplied to the refrigerant heat
exchanger 500b (portion A of FIG. 3). If necessary, a separate heat
exchanging device which may exchange heat between the boil-off
gases upstream and downstream of the refrigerant decompressing
device may be additionally provided.
[0067] As described above, the system of the present embodiments
can re-liquefy and store the boil-off gas generated from the
storage tank fluid cargo, thereby increasing the transportation
rate of the fluid cargo. In particular, even when the consumption
of fuel on the in-ship gas consumption places is small, the gas can
be combusted by the gas combustion unit (GCU) or the like to
prevent the pressure of the storage tank from increasing to reduce
or eliminate the amount of wasted cargo, thereby preventing a waste
of energy.
[0068] In addition, the boil-off gas is circulated as the
refrigerant to be utilized as the cold heat source for
re-liquefaction, thereby effectively re-liquefying the boil-off gas
without configuring the separate refrigerant cycle, and the
separate refrigerant need not be supplied to contribute to securing
the in-ship space and increase the economical efficiency. In
addition, if the refrigerant is insufficient in the refrigerant
cycle, the refrigerant may be replenished from the storage tank to
be smoothly replenished and the refrigerant cycle may be
effectively operated.
[0069] As described above, the boil-off gas may be re-liquefied by
using the cold heat of the boil-off gas itself in multiple steps,
so that the system configuration for treating the in-ship boil-off
gas can be simplified and the cost required to install and operate
the apparatus for complicated boil-off gas treatment can be
saved.
[0070] FIG. 4 is a configuration diagram schematically showing a
boil-off gas treatment system for a ship according to a third
embodiment of the present invention.
[0071] Referring to FIG. 4, the ship of the present embodiment
includes: a boil-off gas heat exchanger 110 which is installed on a
downstream of the storage tank T; a compressor 120 and a first
extra compressor 122 which are installed on a downstream of the
boil-off gas heat exchanger 110 to compress boil-off gas discharged
from the storage tank T; a cooler 130 which lowers temperature of
the boil-off gas compressed by the extra compressor 120; a first
extra cooler 132 which lowers the temperature of the boil-off gas
compressed by the first extra compressor 122; a first valve 191
which is installed on an upstream of the compressor 120; a second
valve 192 which is installed on a downstream of the cooler 130; a
third valve 193 which is installed on an upstream of the first
extra compressor 122; a fourth valve 194 which is installed on a
downstream of the first extra cooler 132; a refrigerant heat
exchanger 140 which additionally cools the boil-off gas cooled by
the boil-off gas heat exchanger 110; a refrigerant decompressing
device 160 which expands the boil-off gas passing through the
refrigerant heat exchanger 140 and then sends the expanded boil-off
gas back to the refrigerant heat exchanger 140; and a first
decompressing device 150 which expands the boil-off gas
additionally cooled by the refrigerant heat exchanger 140.[123]
[0072] The boil-off gas, which is naturally generated from the
storage tank T and then discharged, is supplied to a fuel
consumption source 180 along the first supply line L1. The ship of
the present embodiment may further include an eleventh valve 203
which is installed upstream of the fuel consumption place 180 to
control a flow rate of the boil-off gas sent to the fuel
consumption place 180 and opening/closing thereof.
[0073] The boil-off gas heat exchanger 110 is installed on the
first supply line L1 and recovers cold heat from the boil-off gas
immediately after being discharged from the storage tank T. The
boil-off gas heat exchanger 110 is supplied with the boil-off gas
discharged from the storage tank T and uses the boil-off gas
supplied to the boil-off gas heat exchanger 110 along the return
line L3 as a refrigerant. The fifth valve 195 which controls the
flow rate of the boil-off gas and opening/closing thereof may be
installed on a return line L3.
[0074] The compressor 120 and the first extra compressor 122
compress the boil-off gas passing through the boil-off gas heat
exchanger 110. The compressor 120 is installed on the first supply
line L1 and the first extra compressor 122 is installed on the
second supply line L2. The second supply line L2 is branched from
the first supply line L1 on the upstream of the compressor 120 and
connected to the first supply line L1 on the downstream of the
compressor 120. In addition, the compressor 120 and the first extra
compressor 122 are installed in parallel, and may have the same
performance.
[0075] In general, the ship is additionally provided with the first
extra compressor 122 and the first extra cooler 132 for preparing
for the case where the compressor 120 and the cooler 130 fail.
Typically, the first extra compressor 122 and the first extra
cooler 132 are not used at ordinary times when the compressor 120
or the cooler 130 does not fail.
[0076] That is, typically, at ordinary times when the compressor
120 or the cooler 130 does not fail, the third valve 193 on an
upstream of the first extra compressor 122 and the fourth valve 194
on a downstream of the first extra cooler 132 are closed so that
the boil-off gas is supplied to the fuel consumption place 180 via
the compressor 120 and the cooler 130, and when the compressor 120
or the cooler 130 fails, the third valve 193 on the upstream of the
first extra compressor 122 and the fourth valve 194 on the
downstream of the first extra cooler 132 are open and the first
valve 191 on the upstream of the compressor 120 and the second
valve 192 on a downstream of the cooler 130 are closed so that the
boil-off gas is supplied to the fuel consumption place 180 via the
first extra compressor 122 and the first extra cooler 132.
[0077] The present invention is to increase the re-liquefaction
efficiency and re-liquefaction amount of the boil-off gas by using
the first extra compressor 122 and the first extra cooler 132 which
are not used even if they are installed in the ship, and sends a
part of the boil-off gas compressed by the first extra compressor
122 to the fuel consumption place 180 and uses the other part of
the boil-off gas as a refrigerant which additionally cools the
boil-off gas in the refrigerant heat exchanger 140.
[0078] FIG. 6 is a graph schematically illustrating a phase change
of methane depending on temperature and pressure. Referring to FIG.
6, methane becomes a supercritical fluid state at a temperature of
approximately -80.degree. C. or higher and a pressure of
approximately 55 bars or higher. That is, in the case of methane, a
critical point is approximately -80.degree. C. and 55 bars. The
supercritical fluid state is a third state different from a liquid
phase or a gas phase.
[0079] On the other hand, if the supercritical fluid states has a
temperature lower than the critical point at a pressure equal to or
higher than the critical point, it may also be a state in which a
density is high, unlike a general liquid phase. Here, the state of
the boil-off gas having a pressure equal to or higher than the
critical point and a temperature equal to lower than the critical
point is referred to as a "high-pressure liquid phase".
[0080] The boil-off gas compressed by the compressor 120 or the
first extra compressor 122 may be in a gaseous state or in a
supercritical fluid state depending on how much the boil-off gas is
compressed.
[0081] When the boil-off gas sent to the boil-off gas heat
exchanger 110 through the return line L3 is in a gas phase, the
temperature of the boil-off gas is lowered while the boil-off gas
passes through the boil-off gas heat exchanger 110, and thus the
boil-off gas may be a mixed state of liquid and gas. In the case of
the supercritical fluid state, the temperature of the boil-off gas
is lowered while the boil-off gas passes through the boil-off gas
heat exchanger 110 and thus the boil-off gas may be the
"high-pressure liquid phase".
[0082] The temperature of the boil-off gas cooled by the boil-off
gas heat exchanger 110 is further lowered while the boil-off gas
passes through the refrigerant exchanger 140. When the boil-off gas
passing through the boil-off gas heat exchanger 110 is in the mixed
state of liquid and gas, the temperature of the boil-off gas is
further lowered while the boil-off gas passes through the
refrigerant heat exchanger 140 and thus the boil-off gas becomes
the mixed state in which a ratio of liquid is higher or becomes the
liquid phase and in the case of the "high-pressure liquid phase",
the temperature of the boil-off gas is further lowered while the
boil-off gas passes through the refrigerant heat exchanger 140.
[0083] Further, even when the boil-off gas which passes through the
refrigerant heat exchanger 140 is in the "high-pressure liquid
phase", the pressure of the boil-off gas is lowered while the
boil-off gas passes through the first decompressing device 150, and
thus the boil-off gas becomes low in a liquid phase or the mixed
state of liquid and gas.
[0084] It can be appreciated that even if the pressure of the
boil-off gas is lowered to the same level (P in FIG. 6) by the
first decompressing device 150, the boil-off gas becomes the mixed
state in which the ration of the liquid is higher in the case where
the boil-off gas is decompressed in the higher temperature
(X.fwdarw.X' in FIG. 6) than in the case where the boil-off gas is
decompressed in the lower temperature (Y.fwdarw.Y' in FIG. 6).
Further, it can be appreciated that if the temperature may be
further lowered, the boil-off gas can theoretically be re-liquefied
100% (Z.fwdarw.Z' in FIG. 6). Therefore, if the boil-off gas is
cooled once more by the refrigerant heat exchanger 140 before
passing through the first decompressing device 150, the
re-liquefaction efficiency and the liquefaction amount can be
increased.
[0085] Referring back to FIG. 4, compared with the first and second
embodiments in which the refrigerant circulators 300a and 300b for
additionally cooling the boil-off gas are configured as the closed
loop, the present embodiment is different from the first and second
embodiments in that the refrigerant cycle is configured as the open
loop.
[0086] In the first and second embodiments, the refrigerant
circulators 300a and 300b are configured as the closed loop, and
thus the boil-off gas compressed by the refrigerant compressors
310a and 310b is used only as a refrigerant in the refrigerant heat
exchangers 500a and 500b but may not be sent to the fuel
consumption place or may not undergo the re-liquefaction
process.
[0087] On the other hand, in the present embodiment, the
refrigerant cycle is configured as the open loop, and thus the
boil-off gas compressed by the first extra compressor 122 is joined
with the boil-off gas compressed by the compressor 120, and then a
part of the boil-off gas is sent to the fuel consumption place 180,
the other part thereof is used as the refrigerant in the
refrigerant heat exchanger 140 along the recirculation line L5, and
the remaining part thereof undergoes the re-liquefaction process
along the return line L3.
[0088] The recirculation line L5 is a line which is branched from
the first supply line L1 on the downstream of the compressor 120
and connected to the first supply line L1 on the upstream of the
compressor 120. A sixth valve 196 which controls the flow rate of
the boil-off gas and the opening/closing thereof may be installed
on the recirculation line L5 along which the boil-off gas branched
from the first supply line L1 is sent to the refrigerant heat
exchanger 140.
[0089] Compared with the first and second embodiments in which the
refrigerant cycle is configured as the closed loop, the present
embodiment in which the refrigerant cycle is configured as the open
loop is greatly different from the first and second embodiments in
that the downstream line of the compressor 120 and the downstream
line of the first extra compressor 122 are connected. That is, in
the present embodiment, the second supply line L2 on the downstream
of the first extra compressor 122 is connected to the first supply
line L1 on the downstream of the compressor 120, and thus the
boil-off gas compressed by the first extra compressor 122 is joined
with the boil-off gas compressed by the compressor 120 and then
sent to the refrigerant heat exchanger 140, the fuel consumption
place 180, or the boil-off gas heat exchanger 110. The present
embodiment includes all other modifications in which the downstream
of the compressor 120 and the downstream line of the first extra
compressor 122 are connected.
[0090] Therefore, according to the present embodiment, upon the
increase in the demanded amount of the fuel consumption place 180
such as the increase in the operating speed of the ship, the
boil-off gas compressed by the first extra compressor 122 as well
as the boil-off gas compressed by the compressor 120 as well as the
compressed may be sent to the fuel consumption place 180.
[0091] Generally, however, since the compressor 120 and the first
extra compressor 122 are designed to have a capacity of
approximately 1.2 times the amount required in the fuel consumption
place 180, the case in which the boil-off gas compressed by the
first extra compressor 122 exceeding the capacity of the compressor
120 is sent to the fuel consumption place 180 little occurs.
Rather, since the boil-off gas discharged from the storage tank T
are entirely not consumed in the fuel consumption place 180 and
therefore the boil-off gas to be re-liquefied increases, the case
in which a large amount of refrigerant is required to re-liquefy a
large amount of boil-off gas is more frequent.
[0092] According to the present embodiment, since not only the
boil-off gas compressed by the compressor 120 but also the boil-off
gas compressed by the first extra compressor 122 may be used as the
refrigerant for the heat exchange in the refrigerant heat exchanger
140, the boil-off gas supplied to the refrigerant heat exchanger
140 along the return line L3 after passing through the boil-off gas
heat exchanger 110 may be cooled to a lower temperature by using
more refrigerant and the overall re-liquefaction efficiency and
re-liquefaction amount may be increased. Theoretically, 100%
re-liquefaction is possible.
[0093] Generally, upon determining the capacity of the compressors
120 and 122 provided in the ship, both of the capacity required for
supplying the boil-off gas to the fuel consumption place 180 and
the capacity required for re-liquefying the boil-off gas remaining
by being not completely consumed in the fuel consumption place 180
are considered. According to the present embodiment, since the
re-liquefaction amount may be increased by using the extra
compressor 122, the capacity required for re-liquefaction may be
reduced, and thus small-capacity compressors 120 and 122 can be
provided. Reducing the capacity of the compressor can save both
equipment installation costs and operating costs.
[0094] In the present embodiment, at ordinary times when the
compressor 120 or the cooler 130 does not fail, not only the first
valve 191 and the second valve 192 but also the third valve 193 and
the fourth valve 194 are open so that all of the compressor 120,
the cooler 130, the first extra compressor 122, and the first extra
cooler 132 are operated, and when the compressor 120 or the cooler
130 fails, increasing the re-liquefaction efficiency and the
re-liquefaction amount is abandoned and the first valve 191 and the
second valve 192 are closed so that the system is operated only by
the boil-off gas passing through the first extra compressor 122 and
the first extra compressor 132.
[0095] For convenience of explanation, it is described that the
compressor 120 and the cooler 130 play a major role and the first
extra compressor 122 and the first extra cooler 132 play an
auxiliary role. However, the compressor 120 and the first extra
compressor 122 and the cooler 130 and the first extra cooler 132
play the same role. At least two compressors and coolers which play
the same role are provided in one ship, and therefore when any one
of the two compressors fail, the other unbroken compressor may be
used, which may satisfy a redundancy concept. Next, the above
description is applied.
[0096] Therefore, as in the case in which the compressor 120 or the
cooler 130 fails, even in the case in which the first extra
compressor 122 or the first extra cooler 132 fails, increasing the
re-liquefaction efficiency and the re-liquefaction amount is
abandoned, and the third valve 193 and the fourth valve 194 are
closed so that the system is operated only the boil-off gas passing
through the compressor 120 and the cooler 130.
[0097] On the other hand, when the ship is operated at a high speed
enough that most or all of the boil-off gas discharged from the
storage tank T can be used as fuel for the fuel consumption place
180, there is little or no amount of boil-off gas. Accordingly,
when the ship is operated at a high speed, only one of the
compressor 120 and the first extra compressor 122 may be
operated.
[0098] The compressor 120 and the first extra compressor 122 may
compress the boil-off gas to a pressure required by the fuel
consumption place 180. The fuel consumption place 180 may be an
engine, a generator, or the like which are operated by the boil-off
gas as fuel. For example, if the fuel consumption place 180 is a
boost engine for a ship, the compressor 120 and the first extra
compressor 122 may compress the boil-off gas to a pressure of
approximately 10 to 100 bars.
[0099] In addition, the compressor 120 and the first extra
compressor 122 may also compress the boil-off gas to a pressure of
approximately 150 bars to 400 bars when the fuel consumption place
180 is an ME-GI engine, and when the fuel consumption place 180 is
a DFDE, the boil-off gas may be compressed to a pressure of
approximately 6.5 bars, and when the fuel consumption place 180 is
an X-DF engine, the boil-off gas may be compressed to a pressure of
approximately 16 bars.
[0100] The fuel consumption place 180 may also include various
kinds of engines. For example, when the fuel consumption place 180
includes the X-DF engine and the DFDE, the compressor 120 and the
first extra compressor 122 may compress the boil-off gas to the
pressure required by the X-DF engine, and the decompressing device
is installed on the upstream of the DFDE to lower a part of the
boil-off gas compressed at the pressure required by the X-DF engine
to a pressure required by the DFDE and then supply the compressed
boil-off gas to the DFDE.
[0101] In addition, in order to increase the re-liquefaction
efficiency and the re-liquefaction amount in the boil-off gas heat
exchanger 110 and the refrigerant heat exchanger 140, the
compressor 120 or the first extra compressor 122 compresses the
boil-off gas so that the pressure of the boil-off gas exceeds the
pressure required by the fuel consumption place 180, and the
decompressing device is installed on the upstream of the fuel
consumption place 180 to lower the pressure of the compressed
boil-off gas to exceed the pressure required by the fuel
consumption place 180 to the pressure required by the fuel
consumption place 180 and then supply the compressed boil-off gas
to the fuel consumption place 180.
[0102] Meanwhile, the compressor 120 and the first extra compressor
122 may each be a multi-stage compressor. FIG. 4 illustrates that
one compressor 120 or 122 compresses the boil-off gas to the
pressure required by the fuel consumption place 180, but when the
compressor 120 and the first extra compressor 122 are a multi-stage
compressor, a plurality of compression cylinders may compress the
boil-off gas to the pressure required by the fuel consumption place
180 several times.
[0103] When the compressor 120 and the first extra compressor 122
are a multi-stage compressor, the plurality of compression
cylinders may be provided in the compressor 120 and the first extra
compressor 122 in series and the plurality of coolers may each be
provide on the downstream of the plurality of compression
cylinders.
[0104] The cooler 130 of the present embodiment is installed
downstream of the compressor 120 to cool the boil-off gas which is
compressed by the compressor 120 and has the increased pressure and
temperature. The first extra cooler 132 of the present embodiment
is installed downstream of the first extra compressor 122 to cool
the boil-off gas which is compressed by the first extra compressor
122 and has the increased pressure and temperature. The cooler 130
and the first extra cooler 132 may cool the boil-off gas by
exchanging heat with seawater, fresh water, or air introduced from
the outside.
[0105] The refrigerant heat exchanger 140 of the present embodiment
additionally cools the boil-off gas which is cooled by the boil-off
gas heat exchanger 110 and then supplied to the refrigerant heat
exchanger 140 along the return line L3. The refrigerant
decompressing device 160 of the present embodiment expands the
boil-off gas which passes through the refrigerant heat exchanger
140 and then sends the expanded boil-off gas back to the
refrigerant heat exchanger 140.
[0106] That is, the refrigerant heat exchanger 140 expands the
boil-off gas, which passes through the boil-off gas heat exchanger
110 and then supplied to the refrigerant heat exchanger 140 along
the return line L3, performs heat exchange by the refrigerant to
additionally cool the boil-off gas expanded by the refrigerant
decompressing device 160.
[0107] The refrigerant decompressing device 160 of the present
embodiment may be various means for lowering the pressure of the
fluid, and the state of the fluid just before passing through the
refrigerant decompressing device 160 and the state of the fluid
just after passing through the refrigerant decompressing device 160
may be changed depending on the operation condition of the system.
However, when the refrigerant decompressing device 160 is an
expander, in order to prevent a physical damage of the refrigerant
decompressing device 160, the fluid just before passing through the
refrigerant decompressing device 160 and the fluid just after
passing through the refrigerant decompressing device 160 is
preferably maintained in a gas phase. Next, the above description
is applied.
[0108] By means of the boil-off gas used as the refrigerant for the
heat exchange in the refrigerant heat exchanger 140 after passing
through the refrigerant decompressing device 160, after the
boil-off gas compressed by the compressor 120 is joined with the
boil-off gas compressed by the first extra compressor 122, a part
of the joined boil-off gas is supplied to the refrigerant heat
exchanger 140 along the recirculation line L5 and cooled by
exchanging heat with the boil-off gas, which passes through the
refrigerant decompressing device 160, in the refrigerant heat
exchanger 140 by the refrigerant and then supplied to the
refrigerant decompressing device 160.
[0109] In addition, the boil-off gas supplied from the first supply
line L1 to the refrigerant heat exchanger 140 along the first
supply line L1 is primarily used in the refrigerant heat exchanger
140 and is additionally cooled by the refrigerant decompressing
device 160 and is then sent back to the refrigerant heat exchanger
140, such that the boil-off gas is used as the refrigerant.
[0110] That is, the flow of the boil-off gas compressed by the
compressor 120 supplied to the refrigerant heat exchanger 140 along
the recirculation line L5 after being joined with the boil-off gas
compressed by the first extra compressor 122 and the boil-off gas
which passes through the boil-off gas heat exchanger 110 and is
then supplied to the refrigerant heat exchanger 140 along the
return line L3 exchange heat with each other by means of the
boil-off gas, which passes through the refrigerant decompressing
device 160, as a refrigerant to be cooled.
[0111] The first decompressing device 150 of the present embodiment
is installed on the return line L3 to expand the boil-off gas
cooled by the boil-off gas heat exchanger 110 and the refrigerant
heat exchanger 140. The boil-off gas compressed by the compressor
120 is joined with the boil-off gas compressed by the first extra
compressor 122 and then a part of the boil-off gas is branched into
pass through the boil-off gas heat exchanger 110, the refrigerant
heat exchanger 110 140, and the first decompressing device 150,
such that the boil-off gas is partially or totally
re-liquefied.
[0112] The first decompressing device 150 includes all means which
may expand and cool the boil-off gas, and may be an expansion
valve, such as a Joule-Thomson valve, or an expander.
[0113] The ship of the present embodiment may include the
gas-liquid separator 170 which is installed on the return line L3
on the downstream of the first decompressing device 150 and
separates the gas-liquid mixture discharged from the first
decompressing device 150 into gas and liquid.
[0114] When the ship of the present embodiment does not include the
gas-liquid separator 170, the liquid or the boil-off gas in the
gas-liquid mixed state which passes through the first decompressing
device 150 is immediately sent to the storage tank T.
[0115] When the ship of the present embodiment includes the
gas-liquid separator 170, the boil-off gas which passes through the
first decompressing device 150 is sent to the gas-liquid separator
170 to separate the gas phase and the liquid phase. The liquid
separated by the gas-liquid separator 170 returns to the storage
tank T along the return line L3 and the gas separated by the
gas-liquid separator 170 is supplied to the boil-off gas heat
exchanger 110 along a gas discharge line which extends from the
gas-liquid separator 170 to the first supply line L1 on the
upstream of the boil-off gas heat exchanger 110.
[0116] When the ship of the present embodiment includes the
gas-liquid separator 170, the ship may further include a seventh
valve 197 which controls the flow rate of the liquid separated by
the gas-liquid separator 170 and sent to the storage tank T; an
eighth valve 198 which controls the flow rate of gas separated by
the gas-liquid separator 170 and sent to the boil-off gas heat
exchanger 110.
[0117] The first to eighth valves and the eleventh valve 191, 192,
193, 194, 195, 196, 197, 198, and 203 of the present embodiment may
be manually controlled by allowing a person to directly determine
the operation condition of the system and may be automatically
controlled to be opened or closed depending on a preset value.
[0118] The main flow of the boil-off gas is defined to easily
describe the operation of the device for re-liquefaction of
boil-off gas according to an embodiment of the present invention. A
flow in which the boil-off gas generated from the storage tank T
and the gas discharged from the gas-liquid separator 170 is
supplied to the boil-off gas heat exchanger 110 is defined as a
first flow 100, a flow which is supplied from the boil-off gas heat
exchanger 110 to the compressor 120 and the first extra compressor
122 and then discharged from the compressor 120 or the first extra
compressor 122 and supplied to the fuel consumption place 180 is
defined as a second flow 102, a flow which is branched from the
second flow 102 on the downstream of the compressor 120 and the
first extra compressor 122 and the supplied to the refrigerant heat
exchanger 140 is defined as a third flow 104, a flow which is
branched from the second flow 102 on the downstream of the
compressor 120 and the first extra compressor 122 and supplied to
the boil-off gas heat exchanger 110 is defined as a fourth flow
106, and a flow which is supplied from the boil-off gas heat
exchanger 110 to the refrigerant heat exchanger 140 is defined as a
fifth flow 108. The first flow 100 becomes the second flow while
passing through the boil-off heat exchanger 110 and the fourth flow
106 becomes the fifth flow 108 while passing through the boil-off
heat exchanger 110.
[0119] Hereinafter, an operation of an apparatus for
re-liquefaction of boil-off gas re-according to an embodiment of
the present invention will be described with reference to FIG. 4.
The present embodiment is particularly suitable for the case where
the liquefied gas stored in the storage tank is liquefied natural
gas and the fuel consumption place is X-DF, but is not limited
thereto. The same goes for the fourth embodiment.
[0120] The gaseous boil-off gas generated from the storage tank (T)
storing the liquefied gas in the liquid phase is supplied to the
boil-off gas heat exchanger (110). At this time, the gaseous
boil-off gas generated from the storage tank T meets the gaseous
boil-off gas discharged from the gas-liquid separator 170 after the
predetermined time elapses from the operation of the system to form
the first flow 100. Ultimately, the boil-off gas supplied to the
boil-off gas heat exchanger 110 becomes the first flow 100.
[0121] The boil-off gas heat exchanger 110 serves to recover the
cold heat of the first flow 100 to cool the other boil-off gas.
That is, the boil-off heat exchanger 110 recovers the cold heat of
the first flow 100 and delvers the recovered cold heat to the flow
supplied back to the boil-off heat exchanger 110 in the second flow
102, that is, the fourth flow 106.
[0122] Accordingly, in the boil-off heat exchanger 110, the heat
exchange is generated between the first flow 100 and the fourth
flow 106 so that the first flow 100 is heated and the fourth flow
106 is cooled. The heated first flow 100 becomes the second flow
102 and the cooled fourth flow 106 becomes the fifth flow 108.
[0123] The second flow 102 discharged from the boil-off gas heat
exchanger 110 is supplied to the compressor 120 or the first extra
compressor 122 and is compressed by the compressor 120 or the first
extra compressor 122.
[0124] A part of the second flow 102 in which the boil-off gas
compressed by the compressor 120 and the boil-off gas compressed by
the first extra compressor 122 are joined is the third flow 104 and
supplied to the refrigerant heat exchanger 140 as a refrigerant,
and the other part thereof is the fourth flow 106 and is supplied
to the boil-off gas heat exchanger 110 to be cooled and the
remaining part thereof is supplied to the fuel consumption place
180.
[0125] The third flow 104 supplied to the refrigerant heat
exchanger 140 is discharged from the refrigerant heat exchanger 140
and expanded in the refrigerant decompressing device 160 and then
supplied back to the refrigerant heat exchanger 140. At this time,
the third flow 104 primarily supplied to the refrigerant heat
exchanger 140 is expanded in the refrigerant heat exchanger 140 and
then exchanges heat with the third flow 104 supplied back to the
refrigerant heat exchanger 140 to be cooled. The third flow 104
which passes through the refrigerant decompressing device 160 and
the refrigerant heat exchanger 140 is joined with the second flow
102 that is discharged from the boil-off gas heat exchanger 110 and
supplied to the compressor 120 or the first extra compressor
122.
[0126] The fourth flow 106 cooled by the heat exchange with the
first flow 100 in the boil-off gas heat exchanger 110 becomes the
fifth flow 108 and is supplied to the refrigerant heat exchanger
140. The fifth flow 108 supplied to the refrigerant heat exchanger
140 exchanges heat with the third flow 104 which passes through the
refrigerant decompressing device 160 and is cooled, and then passes
through the first decompressing device 150 and expanded. The fifth
flow 108 which passes through the first decompressing device 150
becomes a gas-liquid mixture state in which gas and liquid are
mixed.
[0127] The fifth flow 108 in the gas-liquid mixture state is
immediately sent to the storage tank T or separated into gas and
liquid while passing through the gas-liquid separator 170. The
liquid separated by the gas-liquid separator 170 is supplied to the
storage tank T and the gas separated by the gas-liquid separator
170 is supplied back to the boil-off gas heat exchanger 110,
thereby repeating the above-mentioned series of processes.
[0128] FIG. 5 is a configuration diagram schematically showing a
boil-off gas treatment system for a ship according to a fourth
embodiment of the present invention.
[0129] The ship of the fourth embodiment shown in FIG. 5 is
different from the ship of the third embodiment shown in FIG. 4 in
that the ship of the fourth embodiment further includes a third
supply line L7 along which a part of the boil-off gas, which passes
through the boil-off gas heat exchanger 110 and then passes through
the boil-off gas heat exchanger 142 along the return line L3, is
branched and is then sent back to the refrigerant heat exchanger
142 to increase the re-liquefaction efficiency and the
re-liquefaction amount in the refrigerant heat exchanger 142,
further includes a ninth valve 201, a first additional line L6, a
tenth valve 202, and a twelfth valve 205, and a system is
configured to modify some lines in which the boil-off gas flows to
operate the refrigerant cycle as the closed loop as in the first
embodiment and the second embodiment and operate the refrigerant
cycle as the open loop as in the third embodiment. Hereinafter the
difference will be mostly described. The detailed description of
the same member as the ship of the foregoing third embodiment will
be omitted.
[0130] In addition, the fuel consumption places 180 and 181 of the
present embodiment are configured to correspond to the fuel
consumption place 180 of the fourth embodiment. However, to
differentiate the fuel consumption place 180 using the
high-pressure boil-off gas as fuel from the fuel consumption place
181 using the low-pressure boil-off gas, the fuel consumption place
using the high-pressure boil-off gas as fuel is referred to as a
high pressure engine 180 and or the fuel demanding unit 180 and the
fuel consumption place using the low-pressure boil-off gas is
referred to a low-pressure engine 181.
[0131] The `high pressure` of the high pressure engine 180 means
that it uses a higher pressure fuel than the low pressure engine
181 and may be an X-DF engine as well as an ME-GI engine, which is
generally classified as a high pressure engine. The low pressure
engine 181 may be a DF engine or a gas turbine and the low pressure
engine 181 may be the X-DF engine if the high pressure engine 180
is an ME-GI engine. Next, the above description is applied.
[0132] Referring to FIG. 5, similar to the third embodiment, the
ship of the present embodiment includes the boil-off gas heat
exchanger 110, the first valve 191, the compressor 120, the cooler
130, the second valve 192, the third valve 193, the extra
compressor 122, the extra cooler 132, the fourth valve 194, the
refrigerant heat exchanger 142, the refrigerant decompressing
device 160, and the first decompressing device 150.
[0133] However, unlike the third embodiment, the ship of the
present embodiment further includes: a third decompressing device
153 which is installed on the third supply line L7 on an upstream
of the refrigerant heat exchanger 142; a first additional line L6
which connects between the recirculation line L5 and the second
supply line L2; a ninth valve 201 which is installed on the
recirculation line L5; a tenth valve 202 which is installed on the
first additional line L6; and a twelfth valve 205 which is
installed on the recirculation line L5 between the second supply
line L2 and the refrigerant heat exchanger 142.
[0134] Unlike the third embodiment which selectively includes the
sixth valve 196, the ship of the present embodiment essentially
includes the sixth valve 196 which is installed on the
recirculation line L5 along which the boil-off gas branched from
the first supply line L1 is sent to the refrigerant heat exchanger
142 to control the flow rate and of the boil-off gas the
opening/closing thereof.
[0135] Similar to the third embodiment, the storage tank T stores
liquefied gas such as liquefied natural gas and liquefied ethane
gas, and discharges the boil-off gas to the outside when the
internal pressure of the storage tank T exceeds a certain pressure
or higher. The boil-off gas discharged from the storage tank (T) is
sent to the boil-off gas heat exchanger 110.
[0136] Similar to the third embodiment, the boil-off gas heat
exchanger 110 of the present embodiment uses the boil-off gas
discharged from the storage tank T as the refrigerant and cools the
boil-off gas supplied to the boil-off gas heat exchanger 110 along
the return line L3. The fifth valve 195 which controls the flow
rate of the boil-off gas and opening/closing thereof may be
installed on a return line L3.
[0137] Similar to the third embodiment, the compressor 120 of the
present embodiment is installed on the first supply line L1 to
compress the boil-off gas discharged from the storage tank T and
similar to the third embodiment, the extra compressor 122 of the
present embodiment is installed in parallel with the compressor 120
on the second supply line L2 to compress the boil-off gas
discharged from the storage tank T. The compressor 120 and the
extra compressor 122 may be a compressor having the same
performance, and each may be a multi-stage compressor.
[0138] Similar to the third embodiment, the ship of the present
embodiment may further include an eleventh valve 203 which is
installed on the upstream of the high-pressure engine 180 to
control a flow rate of the boil-off gas sent to the high pressure
engine 180 and the opening/closing thereof.
[0139] Similar to the third embodiment, the ship of the present
embodiment uses the boil-off gas compressed by the extra compressor
122 as the refrigerant which additionally cools the boil-off gas in
the refrigerant heat exchanger 142, thereby increasing the
re-liquefaction efficiency and the re-liquefaction amount.
[0140] Similar to the third embodiment, the cooler 130 of the
present embodiment is installed downstream of the compressor 120 to
cool the boil-off gas that passes through the compressor 120 and
has the increased pressure and temperature. Similar to the third
embodiment, the extra cooler 132 of the present embodiment is
installed downstream of the extra compressor 122 to cool the
boil-off gas which passes through the extra compressor 122 and has
the increased pressure and temperature.
[0141] Similar to the third embodiment, the refrigerant heat
exchanger 142 of the present embodiment additionally cools the
boil-off gas which is supplied to the boil-off gas heat exchanger
110 along the return line L3 and cooled by the boil-off gas heat
exchanger 110.
[0142] Similar to the third embodiment, according to the present
embodiment, the boil-off gas discharged from the storage tank T is
further cooled not only in the boil-off gas heat exchanger 110 but
also in the refrigerant heat exchanger 142, and may be supplied to
the first decompressing device 150 in the state in which the
temperature is lower, thereby increasing the re-liquefaction
efficiency and the re-liquefaction amount.
[0143] However, the refrigerant heat exchanger 142 of the present
embodiment is different from the third embodiment in that as a
refrigerant for cooling the boil-off gas supplied to the
refrigerant heat exchanger 142 along the return line L3 after
passing through the boil-off gas heat exchanger 110, the boil-off
gas compressed by the compressor 120 or the extra compressor 122
and then supplied to the refrigerant heat exchanger 142 along the
recirculation line L5 and a fluid passing through the refrigerant
decompressing device 160 and then supplied back to the refrigerant
heat exchanger 142, and a fluid supplied to the refrigerant heat
exchanger 142 along the third supply line L7 are also used. The
fluid supplied to the refrigerant heat exchanger 142 along the
third supply line L7 is a flow in which the fluid passing through
the boil-off gas heat exchanger 110 and the refrigerant heat
exchanger 142 along the return line L3 is partially branched.
[0144] The compressor 120 or the extra compressor 122 compresses
the boil-off gas according to the requirements of the high pressure
engine 180 or a higher pressure than the requirements of the high
pressure engine 180. The boil-off gas compressed by the compressor
120 or the extra compressor 122 essentially undergoes the
decompression process to be sent to the low pressure engine 181.
According to the present embodiment, since not only the pressure
but also the temperature is lowered if the compressed boil-off gas
is decompressed, the fluid decompressed to be sent to the low
pressure engine 181 may be used as a refrigerant in the refrigerant
heat exchanger 142 before being sent to the low pressure engine
181.
[0145] According to the ship of the present embodiment, the cold
heat of the fluid sent to the low pressure engine 181 may be used
to cool the boil-off gas which is subjected to the re-liquefaction
process along the return line L3, thereby more increasing the
re-liquefaction efficiency and the re-liquefaction amount.
[0146] The refrigerant decompressing device 160 of the present
embodiment may be various means for lowering the pressure of the
fluid, and the state of the fluid just before passing through the
refrigerant decompressing device 160 and the state of the fluid
just after passing through the refrigerant decompressing device 160
may be changed depending on the operation condition of the system.
However, when the refrigerant decompressing device 160 is an
expander, in order to prevent a physical damage of the refrigerant
decompressing device 160, the fluid just before passing through the
refrigerant decompressing device 160 and the fluid just after
passing through the refrigerant decompressing device 160 is
preferably maintained in a gas phase.
[0147] By means of the boil-off gas used as the refrigerant for the
heat exchange in the refrigerant heat exchanger 142 after passing
through the refrigerant decompressing device 160, after the
boil-off gas compressed by the compressor 120 is joined with the
boil-off gas compressed by the extra compressor 122, a part of the
joined boil-off gas is supplied to the refrigerant heat exchanger
142 along the recirculation line L5 and cooled by exchanging heat
with the boil-off gas, which passes through the refrigerant
decompressing device 160, in the refrigerant heat exchanger 142 by
the refrigerant and then supplied to the refrigerant decompressing
device 160.
[0148] In addition, the boil-off gas supplied from the first supply
line L1 to the refrigerant heat exchanger 142 along the first
supply line L1 is primarily used in the refrigerant heat exchanger
142 and is additionally cooled by the refrigerant decompressing
device 160 and is then sent back to the refrigerant heat exchanger
142, such that the boil-off gas is used as the refrigerant.
[0149] The first decompressing device 150 of the present embodiment
is installed on the return line L3 to expand the boil-off gas
cooled by the boil-off gas heat exchanger 110 and the refrigerant
heat exchanger 142. The boil-off gas compressed by the compressor
120 is joined with the boil-off gas compressed by the extra
compressor 122 and then a part of the boil-off gas is branched into
pass through the boil-off gas heat exchanger 110, the refrigerant
heat exchanger 142, and the first decompressing device 150, such
that the boil-off gas is partially or totally re-liquefied.
[0150] The third decompressing device 153 of the present embodiment
is installed on the third supply line L7 on the upstream of the
refrigerant heat exchanger 142 to decompress the boil-off gas which
is partially branched from the return line L3 and supplied to the
low pressure engine 181. The third decompressing device 153 may
decompress the boil-off gas to the pressure required by the low
pressure engine 181.
[0151] The first decompressing device 150 and the third
decompressing device 153 include all means which may expand and
cool the boil-off gas, and may be an expansion valve, such as a
Joule-Thomson valve, or an expander.
[0152] The ship of the present embodiment may include the
gas-liquid separator 170 which is installed on the return line L3
on the downstream of the first decompressing device 150 and
separates the gas-liquid mixture discharged from the first
decompressing device 150 into gas and liquid.
[0153] When the ship of the present embodiment does not include the
gas-liquid separator 170, the liquid or the boil-off gas in the
gas-liquid mixed state which passes through the first decompressing
device 150 is immediately sent to the storage tank T.
[0154] When the ship of the present embodiment includes the
gas-liquid separator 170, the boil-off gas which passes through the
first decompressing device 150 is sent to the gas-liquid separator
170 to separate the gas phase and the liquid phase. The liquid
separated by the gas-liquid separator 170 returns to the storage
tank T along the return line L3 and the gas separated by the
gas-liquid separator 170 is supplied to the boil-off gas heat
exchanger 110 along a gas discharge line which extends from the
gas-liquid separator 170 to the first supply line L1 on the
upstream of the boil-off gas heat exchanger 110.
[0155] When the ship of the present embodiment includes the
gas-liquid separator 170, the ship may further include a seventh
valve 197 which controls the flow rate of the liquid separated by
the gas-liquid separator 170 and sent to the storage tank T; an
eighth valve 198 which controls the flow rate of gas separated by
the gas-liquid separator 170 and sent to the boil-off gas heat
exchanger 110.
[0156] One side of the first additional line L6 of the present
embodiment is connected to a recirculation line (not shown) which
is expanded by the refrigerant decompressing device 160 and then
sent to the first supply line L1 through the refrigerant heat
exchanger 142 L5 and the other side thereof is connected to the
second supply line L2 between the third valve 193 and the extra
compressor 122.
[0157] The ninth valve 201 of the present embodiment is installed
on the recirculation line L5 between the point where the
recirculation line L5 meets the first supply line L1 on the
upstream of the compressor 120 and the extra compressor 122 and the
point where the recirculation line L5 meets the first additional
line L6, thereby controlling the flow rate of the fluid and the
opening/closing thereof.
[0158] The twelfth valve 205 of the present embodiment is installed
on the recirculation line L5 between the second supply line L2 and
the refrigerant heat exchanger 142 to control the flow rate of the
fluid and the opening and closing thereof.
[0159] In addition, the ship of the present embodiment is different
from the third embodiment in that the second supply line L2 on the
downstream of the extra compressor 122 is connected to the
recirculation line L5 instead of the first supply line L1.
[0160] The first to twelfth valves and the eleventh valve 191, 192,
193, 194, 195, 196, 197, 198, 201, 202, 203, and 205 of the present
embodiment may be manually controlled by allowing a person to
directly determine the operation condition of the system and may be
automatically controlled to be opened or closed depending on a
preset value.
[0161] Unlike the third embodiment, according to the ship of the
present embodiment, the refrigerant cycle may be operated not only
as the open loop but also as the closed loop so as to more flexibly
use the re-liquefaction system according to the operating
conditions of the ship. Hereinafter, a method of operating a
refrigerant cycle as the closed loop and a method of operating a
refrigerant cycle as the open loop by a valve control will be
described.
[0162] To operate the refrigerant cycle of the ship of the present
embodiment as the closed loop, the system is operated while the
first valve 191, the second valve 192, the third valve 193, the
fourth valve 194, the tenth valve 202, and the twelfth valve 205
are open, and the sixth valve 196 and the ninth valve 201 are
closed.
[0163] If the boil-off gas which is discharged from the storage
tank T and then compressed by the extra compressor 122 is supplied
to the recirculation line L5, the third valve 193 is closed to form
the refrigerant cycle of the closed loop in which the boil-off gas
circulates the extra compressor 122, the extra cooler 132, the
fourth valve 194, the twelfth valve 205, the refrigerant heat
exchanger 142, the refrigerant decompressing device 160, the
refrigerant heat exchanger 142, and the tenth valve 202.
[0164] When the refrigerant cycle is configured as the closed loop,
nitrogen gas may be used as the refrigerant circulating the closed
loop. In this case, the ship of the present embodiment may further
include the pipe through which the nitrogen gas is introduced into
the refrigerant cycle of the closed loop.
[0165] When the refrigerant cycle is operated as the closed loop,
only the boil-off gas circulating the closed loop is used as the
refrigerant in the refrigerant heat exchanger 142. The boil-off gas
passing through the compressor 120 is not introduced into the
refrigerant cycle but is supplied to the high-pressure engine 180
or undergoes the re-liquefaction process along the return line L3.
Therefore, a predetermined flow rate of boil-off gas is circulated
as the refrigerant in the refrigerant heat exchanger 142
irrespective of the re-liquefaction amount or the amount of
boil-off gas required by the high pressure engine 180.
[0166] The flow of the boil-off gas in the case where the
refrigerant cycle of the ship of the present embodiment is operated
as the closed loop will be described as follows.
[0167] The boil-off gas discharged from the storage tank T passes
through the boil-off gas heat exchanger 110 and then compressed by
the compressor 120, and a part thereof is cooled by the cooler 130
and then sent to the fuel consumption place 180, and the remaining
part thereof is sent to the boil-off gas heat exchanger 110 along
the return line L3. The boil-off gas sent to the boil-off gas heat
exchanger 110 along the return line L3 exchanges heat with the
boil-off gas discharged from the storage tank T to be cooled and is
then heat-exchanged in the refrigerant heat exchanger 142 to be
additionally cooled.
[0168] The boil-off gas cooled by the boil-off gas heat exchanger
110 and the refrigerant heat exchanger 142 is branched into two
flows so that one flow is continuously supplied to the first
decompressing device 150 along the return line L3 and the other
flow is supplied to the third decompressing device 153 along the
third supply line L7.
[0169] The boil-off gas supplied to the first decompressing device
150 along the return line L3 is expanded by the first decompressing
device 150 to be partially or totally re-liquefied. When the ship
of the present embodiment does not include the gas-liquid separator
170, the partially or totally re-liquefied boil-off gas is directly
sent to the storage tank T and when the ship of the present
embodiment includes the gas-liquid separator 170, the partially or
totally re-liquefied boil-off gas is sent to the gas-liquid
separator 170. The gas separated by the gas-liquid separator 170 is
joined with the boil-off gas discharged from the storage tank T and
sent to the boil-off gas heat exchanger 110. The liquid separated
by the gas-liquid separator 170 is supplied to the storage tank
T.
[0170] The boil-off gas supplied to the third decompressing device
153 along the third supply line L7 is decompressed by the third
decompressing device 153 and then sent to the refrigerant heat
exchanger 142. The fluid decompressed by the third decompressing
device 153 and having the lowered pressure and temperature is used
as, in the refrigerant heat exchanger 142, the refrigerant cooling
the boil-off gas supplied to the refrigerant heat exchanger 142
along the return line L3 and then supplied to the low pressure
engine 181.
[0171] Meanwhile, the boil-off gas circulating the refrigerant
cycle is compressed by the extra compressor 122, cooled by the
extra cooler 132, and then sent to the refrigerant heat exchanger
142 along the recirculation line L5. The boil-off gas which passes
through the extra compressor 122 and the extra cooler 132 and then
sent to the refrigerant heat exchanger 142 is primarily
heat-exchanged in the refrigerant heat exchanger 142 to be cooled
and then sent to the refrigerant decompressing device 160 to be
secondarily expanded and cooled.
[0172] The boil-off gas which passes through the refrigerant
decompressing device 160 is sent back to the refrigerant heat
exchanger 142 to exchange heat with the boil-off gas passing
through the boil-off gas heat exchanger 110 and then supplied to
the refrigerant heat exchanger 142 along the return line L3, the
boil-off gas decompressed by the third decompressing device 153 and
then supplied to the refrigerant heat exchanger 142 along the third
supply line L7, and the boil-off gas compressed by the extra
compressor 122 supplied to the refrigerant heat exchanger 142 along
the recirculation line L5. The boil-off gas which passes through
the refrigerant decompressing device 160 and then used as the
refrigerant in the refrigerant heat exchanger 142 is sent back to
the extra compressor 122, thereby repeating the above-mentioned
series of processes.
[0173] When the compressor 120 or the cooler 130 fails while the
refrigerant cycle of the ship of the present embodiment is operated
as the closed loop, the first valve 191, the second valve 192, and
the tenth valve 202, and the twelfth valve 205 are closed and the
third valve 193 and the sixth valve 196 are open to allow the
boil-off gas which is discharged from the storage tank T and then
passes through the boil-off gas heat exchanger 110 to be supplied
to the high pressure engine 180 via the third valve 193, the extra
compressor 122, the extra cooler 132, the fourth valve 194, and the
sixth valve 196. When it is necessary to use the boil-off gas
compressed by the extra compressor 122 as the refrigerant of the
refrigerant heat exchanger 142, the ninth valve 201 and the twelfth
valve 205 may be open to operate the system.
[0174] To operate the refrigerant cycle of the ship of the present
embodiment as the open loop, the first valve 191, the second valve
192, the third valve 193, the fourth valve 194, the sixth valve
196, the ninth valve 201, and the twelfth valve 205 are open, and
the tenth valve 202 are closed.
[0175] When the refrigerant cycle is operated as the closed loop,
the boil-off gas circulating the refrigerant cycle and the boil-off
gas sent to the high pressure engine 180 or undergoing the
re-liquefaction process along the return line L3 are separated. On
the other hand, when the refrigerant cycle is operated as the open
loop, the boil-off gas compressed by the compressor 120 and the
boil-off gas compressed by the extra compressor 122 are joined to
be used as a refrigerant in the refrigerant heat exchanger 142, to
be sent to the high pressure engine 180, or to undergo the
re-liquefying process along the return line L3.
[0176] Therefore, if the refrigerant cycle is operated as the open
loop, the flow rate of the refrigerant to be sent to the
refrigerant heat exchanger 142 may be flexibly controlled in
consideration of the re-liquefaction amount and the amount of
boil-off gas required by the high pressure engine 180. In
particular, when the amount of boil-off gas required by the high
pressure engine 180 is small, increasing the flow rate of the
refrigerant sent to the refrigerant heat exchanger 142 may increase
the re-liquefaction efficiency and the re-liquefaction amount.
[0177] That is, when the refrigerant cycle is operated as the
closed loop, it is not possible to supply the refrigerant heat
exchanger 142 with the boil-off gas equal to or more than the
capacity of the extra compressor 122. However, when the refrigerant
cycle is operated as the open loop, the boil-off gas having a flow
rate exceeding the capacity of the extra compressor 122 may be
supplied to the refrigerant heat exchanger 142.
[0178] The flow of the boil-off gas in the case where the
refrigerant cycle of the ship of the present embodiment is operated
as the open loop will be described as follows.
[0179] The boil-off gas discharged from the storage tank T is
branched into two flows after passing through the boil-off gas heat
exchanger 110 and a part thereof is sent to the first supply line
L1 and the remaining part thereof is supplied to the second supply
line L2.
[0180] The boil-off gas sent to the first supply line L1 passes
through the first valve 191, the compressor 120, the cooler 130,
and the second valve 192 and then a part thereof passes through the
sixth valve 196 and the twelfth valve 205 and is sent to the
refrigerant heat exchanger 142, and the other part thereof is again
branched into two flows. One flow of the boil-off gases branched
into the two flows is sent to the high pressure engine 180 and the
other thereof is sent to the boil-off gas heat exchanger 110 along
the return line L3.
[0181] The boil-off gas sent to the second supply line L1 passes
through the third valve 193, the extra compressor 122, the extra
cooler 132, and the fourth valve 194 and then a part thereof is
sent to the refrigerant heat exchanger 142 via the twelfth valve
205 and the other part thereof is sent to the first supply line L1
and then branched into two flows. One flow of the boil-off gases
branched into the two flows is sent to the high pressure engine 180
and the other flow thereof is sent to the boil-off gas heat
exchanger 110 along the return line L3.
[0182] For convenience of explanation, the boil-off gas compressed
by the compressor 120 and the boil-off gas compressed by the extra
compressor 122 are separately described. However, each of the
boil-off gas compressed by the compressor 120 and the boil-off gas
compressed by the extra compressor 122 does not flow separately but
is joined to be supplied to the refrigerant heat exchanger 142, the
high pressure engine 180, or the boil-off gas heat exchanger
110.
[0183] That is, the boil-off gas compressed by the compressor 120
and the boil-off gas compressed by the extra compressor 122 are
mixed, which in turn flows in the recirculation line L5 along which
the boil-off gas is sent to the refrigerant heat exchanger 142, the
first supply line L1 along which the boil-off gas is sent to the
high pressure engine 180, and the return line along which the
boil-off gas is sent to the boil-off gas heat exchanger 110.
[0184] The boil-off gas sent to the refrigerant heat exchanger 142
along the recirculation line L5 is primarily heat-exchanged in the
refrigerant heat exchanger 142 to be cooled, and secondarily
expanded by the refrigerant decompressing device 160 to be cooled
and supplied back to the refrigerant heat exchanger 142. The
boil-off gas which passes through the refrigerant decompressing
device 160 and is supplied to the refrigerant heat exchanger 142
exchanges heat with the boil-off gas passing through the boil-off
gas heat exchanger 110 and then supplied to the refrigerant heat
exchanger 142 along the return line L3, the boil-off gas
decompressed by the third decompressing device 153 and then
supplied to the refrigerant heat exchanger 142 along the third
supply line L7, and a confluent flow of the boil-off gas compressed
by the compressor 120 and the boil-off gas compressed by the extra
compressor 122 which are supplied to the refrigerant heat exchanger
142 along the recirculation line L5.
[0185] The boil-off gas used as the refrigerant in the refrigerant
heat exchanger 142 after passing through the refrigerant
decompressing device 160 is sent to the first supply line L1
through the ninth valve 201 to be discharged from the storage tank
T and then joins with the boil-off gas passing through the boil-off
gas heat exchanger 110, thereby repeating the above-mentioned
series of processes.
[0186] Meanwhile, the boil-off gas sent to the heat exchanger 110
along the return line L3 is cooled by the boil-off gas heat
exchanger 110 and then additionally cooled by the refrigerant heat
exchanger 142. The boil-off gas cooled by the boil-off gas heat
exchanger 110 and the refrigerant heat exchanger 142 is branched
into two flows so that one flow is continuously supplied to the
first decompressing device 150 along the return line L3 and the
other flow is supplied to the third decompressing device 153 along
the third supply line L7.
[0187] The boil-off gas supplied to the first decompressing device
150 along the return line L3 is expanded by the first decompressing
device 150 to be partially or totally re-liquefied. When the ship
of the present embodiment does not include the gas-liquid separator
170, the partially or totally re-liquefied boil-off gas is directly
sent to the storage tank T and when the ship of the present
embodiment includes the gas-liquid separator 170, the partially or
totally re-liquefied boil-off gas is sent to the gas-liquid
separator 170. The gas separated by the gas-liquid separator 170 is
joined with the boil-off gas discharged from the storage tank T and
sent to the boil-off gas heat exchanger 110. The liquid separated
by the gas-liquid separator 170 is supplied to the storage tank
T.
[0188] The boil-off gas supplied to the third decompressing device
153 along the third supply line L7 is decompressed by the third
decompressing device 153 and then sent to the refrigerant heat
exchanger 142. The fluid decompressed by the third decompressing
device 153 and having the lowered pressure and temperature is used
as the refrigerant cooling the boil-off gas supplied to the
refrigerant heat exchanger 142 along the return line L3 and then
supplied to the low pressure engine 181.
[0189] When the compressor 120 or the cooler 130 fails while the
refrigerant cycle of the ship of the present embodiment is operated
as the open loop, the first valve 191, the second valve 192, the
ninth valve 201, and the twelfth valve 205 are closed to allow the
boil-off gas which is discharged from the storage tank T and then
passes through the boil-off gas heat exchanger 110 to be supplied
to the high pressure engine 180 via the third valve 193, the extra
compressor 122, the extra cooler 132, the fourth valve 194, the
sixth valve 196. When it is necessary to use the boil-off gas
compressed by the extra compressor 122 as the refrigerant of the
refrigerant heat exchanger 142, the ninth valve 201 and the twelfth
valve 205 may be open to operate the system.
[0190] When the refrigerant cycle of the ship of the present
embodiment is operated as the open loop, the liquefied gas stored
in the storage tank T is liquefied natural gas, the high pressure
engine 180 is the X-DF engine and the low pressure engine 180 is
the DF engine, temperatures and pressures of fluid at each point
will be described as an example.
[0191] The boil-off gas discharged from the storage tank T is
branched into two after passing through the boil-off gas heat
exchanger 110 to be compressed by the compressor or the extra
compressor 122, and the boil-off gas at point A which is a
confluent flow of the boil-off gas compressed by the compressor 120
and the boil-off gas compressed by extra compressor 122 may be
approximately 43.degree. C. and 17 bars.
[0192] The boil-off gas at point B after the boil-off gas of
approximately 43.degree. C. and 17 bars passes through the
refrigerant heat exchanger 142 may be approximately -74.degree. C.
and 17 bars and the boil-off gas at point C after the boil-off gas
of approximately -74.degree. C. and 17 bars passes through the
refrigerant decompressing device 160 may be approximately
-157.degree. C. and 1 bar. The boil-off gas of approximately
-157.degree. C. and 1 bar passes through the refrigerant heat
exchanger 142 once more and then the boil-off gas at point D may be
approximately 4.5.degree. C. and 1 bar.
[0193] On the other hand, the boil-off gas at point E after the
boil-off gas of approximately 43.degree. C. and 17 bars which is
the confluent flow of the boil-off gas compressed by the compressor
120 and the boil-off gas compressed by the extra compressor 122
passes through the boil-off gas heat exchanger 110 along the return
line L3 may be approximately -97.degree. C. and 17 bar
[0194] The boil-off gas at point F after the boil-off gas of
approximately -97.degree. C. and 17 bars passes through the
refrigerant heat exchanger 142 may be approximately -155.degree. C.
and 17 bars and the boil-off gas at point G after the boil-off gas
of approximately -155.degree. C. and 17 bars passes through the
third refrigerant decompressing device 153 may be approximately
-155.degree. C. and 7 bar. The boil-off gas at point H After the
boil-off gas of approximately -155.degree. C. and 7 bars passes
through the refrigerant heat exchanger 142 once more may be
approximately 40.degree. C. and 7 bar.
[0195] The ship of the present embodiment may independently operate
the extra compressor 122 and the compressor 120 while operating the
refrigerant cycle as the open loop so that the boil-off gas
compressed by the extra compressor 122 is used only as the
refrigerant of the refrigerant heat exchanger 142, the boil-off gas
compressed by the compressor 120 is sent to the high pressure
engine 180 or undergoes the re-liquefaction process along the
return line L3 and is not used as the refrigerant of the
refrigerant heat exchanger 142. Hereinafter, the refrigerant cycle
of the open loop in which the extra compressor 122 and the
compressor 120 are operated independently is referred to as an
`independent open loop`.
[0196] To operate the refrigerant cycle of the ship of the present
embodiment as the independent open loop, the first valve 191, the
second valve 192, the third valve 193, the fourth valve 194, the
ninth valve 201, and the twelfth valve 205 are open, and the sixth
valve 196 and the tenth valve 202 are closed. When the refrigerant
cycle is operated as the independent open loop, the system can be
operated more easily than when the open loop is operated.
[0197] The flow of the boil-off gas in the case where the
refrigerant cycle of the ship of the present embodiment is operated
as the independent open loop will be described as follows.
[0198] The boil-off gas discharged from the storage tank T is
branched into two flows after passing through the boil-off gas heat
exchanger 110 and a part thereof is sent to the first supply line
L1 and the remaining part thereof is supplied to the second supply
line L2. The boil-off gas sent to the first supply line L1 passes
through the first valve 191, the compressor 120, the cooler 130,
and the second valve 192 and then a part thereof is sent to the
high pressure engine 180 and the other part thereof is sent to the
boil-off gas heat exchanger 110 along the return line L3. The
boil-off gas sent to the second supply line L2 passes through the
third valve 193, the extra compressor 122, the extra cooler 132,
the fourth valve 194, and the twelfth valve 205 and is then sent to
the refrigerant heat exchanger 142.
[0199] The boil-off gas which is compressed by the extra compressor
122 and then sent to the refrigerant heat exchanger 142 along the
recirculation line L5 exchanges heat with the boil-off gas which is
primarily heat-exchanged in the refrigerant heat exchanger 142 to
be cooled, secondarily expanded by the refrigerant decompressing
device 160 to be cooled, and then supplied back to the refrigerant
heat exchanger 142 to pass through the boil-off gas heat exchanger
110 and then be supplied to the refrigerant heat exchanger 142
along the return line L3, the boil-off gas which is decompressed by
the third decompressing device 153 and then supplied to the
refrigerant heat exchanger 142 along the third supply line L7, and
the boil-off gas compressed by the extra compressor 122 and then
supplied to the refrigerant heat exchanger 142 along the
recirculation line L5.
[0200] The boil-off gas used as the refrigerant in the refrigerant
heat exchanger 142 after passing through the refrigerant
decompressing device 160 is sent to the first supply line L1
through the ninth valve 201 to be discharged from the storage tank
T and then joins with the boil-off gas passing through the boil-off
gas heat exchanger 110, thereby repeating the above-mentioned
series of processes.
[0201] Meanwhile, the boil-off gas which is compressed by the
compressor 120 and then sent to the heat exchanger 110 along the
return line L3 is cooled by the boil-off gas heat exchanger 110 and
then additionally cooled by the refrigerant heat exchanger 142. The
boil-off gas cooled by the boil-off gas heat exchanger 110 and the
refrigerant heat exchanger 142 is branched into two flows so that
one flow is continuously supplied to the first decompressing device
150 along the return line L3 and the other flow is supplied to the
third decompressing device 153 along the third supply line L7.
[0202] The boil-off gas supplied to the first decompressing device
150 along the return line L3 is expanded by the first decompressing
device 150 to be partially or totally re-liquefied. When the ship
of the present embodiment does not include the gas-liquid separator
170, the partially or totally re-liquefied boil-off gas is directly
sent to the storage tank T and when the ship of the present
embodiment includes the gas-liquid separator 170, the partially or
totally re-liquefied boil-off gas is sent to the gas-liquid
separator 170. The gas separated by the gas-liquid separator 170 is
joined with the boil-off gas discharged from the storage tank T and
sent to the boil-off gas heat exchanger 110. The liquid separated
by the gas-liquid separator 170 is supplied to the storage tank
T.
[0203] The boil-off gas supplied to the third decompressing device
153 along the third supply line L7 is decompressed by the third
decompressing device 153 and then sent to the refrigerant heat
exchanger 142. The fluid compressed by the third decompressing
device 153 and having the lowered pressure and temperature is used
as, in the refrigerant heat exchanger, the refrigerant cooling the
boil-off gas supplied to the refrigerant heat exchanger 142 along
the return line L3 and then supplied to the low pressure engine
181.
[0204] When the compressor 120 or the cooler 130 fails while the
refrigerant cycle of the ship of the present embodiment is operated
as the independent closed loop, the first valve 191, the second
valve 192, the ninth valve 201, and the twelfth valve 205 are
closed and the sixth valve 196 is open to allow the boil-off gas
which is discharged from the storage tank T and then passes through
the boil-off gas heat exchanger 110 to be supplied to the high
pressure engine 180 via the third valve 193, the extra compressor
122, the extra cooler 132, the fourth valve 194, and the sixth
valve 196. When it is necessary to use the boil-off gas compressed
by the extra compressor 122 as the refrigerant of the refrigerant
heat exchanger 142, the ninth valve 201 and the twelfth valve 205
may be open to operate the system.
[0205] The present invention is not limited to the above exemplary
embodiments and therefore it is apparent to a person with ordinary
skill in the art to which the present invention pertains that the
exemplary embodiments of the present invention may be variously
modified or changed without departing from the technical subjects
of the present invention.
* * * * *