U.S. patent application number 15/839458 was filed with the patent office on 2018-08-02 for boil-off gas recovery system.
This patent application is currently assigned to Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). The applicant listed for this patent is Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.). Invention is credited to Kenji NAGURA, Katsuhiro SEYAMA, Satoshi TEZUKA.
Application Number | 20180216878 15/839458 |
Document ID | / |
Family ID | 60293859 |
Filed Date | 2018-08-02 |
United States Patent
Application |
20180216878 |
Kind Code |
A1 |
TEZUKA; Satoshi ; et
al. |
August 2, 2018 |
BOIL-OFF GAS RECOVERY SYSTEM
Abstract
A boil-off gas recovery system 1 includes a tank 2 storing
liquefied gas, an oil supply type compressor 3b for compressing
boil-off gas generated by partial evaporation of the liquefied gas
in the tank 2, and a reliquefying system 9 for liquefying the
boil-off gas compressed by the oil supply type compressor 3b and
returning the liquefied gas that has been liquefied to the tank 2.
The reliquefying system 9 includes a heat exchanger for oil
constituent condensation 11 for cooling down the boil-off gas to a
temperature equal to or lower than a condensation temperature of an
oil constituent contained in the boil-off gas, a separator 14 for
separating the oil constituent condensed by the heat exchanger for
oil constituent condensation 11 from the boil-off gas, and a
reliquefying portion for liquefying the boil-off gas from which the
oil constituent is separated.
Inventors: |
TEZUKA; Satoshi;
(Takasago-shi, JP) ; SEYAMA; Katsuhiro;
(Takasago-shi, JP) ; NAGURA; Kenji; (Takasago-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) |
Hyogo |
|
JP |
|
|
Assignee: |
Kabushiki Kaisha Kobe Seiko Sho
(Kobe Steel, Ltd.)
Hyogo
JP
|
Family ID: |
60293859 |
Appl. No.: |
15/839458 |
Filed: |
December 12, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25J 1/023 20130101;
F25J 1/0025 20130101; F25J 1/0279 20130101; F25J 1/004 20130101;
F25J 1/0297 20130101; F25J 2220/02 20130101; F25J 1/005 20130101;
F25J 1/0202 20130101 |
International
Class: |
F25J 1/00 20060101
F25J001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 2017 |
JP |
2017-014519 |
Claims
1. A boil-off gas recovery system comprising: a tank storing
liquefied gas; an oil supply type compressor for compressing
boil-off gas generated by partial evaporation of the liquefied gas
in the tank; and a reliquefying system for liquefying the boil-off
gas compressed by the oil supply type compressor and returning the
liquefied gas that has been liquefied to the tank, wherein the
reliquefying system includes a heat exchanger for oil constituent
condensation for cooling down the boil-off gas to a temperature
equal to or lower than a condensation temperature of an oil
constituent contained in the boil-off gas, a separator for
separating the oil constituent condensed by the heat exchanger for
oil constituent condensation from the boil-off gas, and a
reliquefying portion for liquefying the boil-off gas from which the
oil constituent is separated.
2. The boil-off gas recovery system according to claim 1, wherein
the reliquefying portion includes a heat exchanger for gas
liquefaction for cooling down the boil-off gas, from which the oil
constituent has been separated by the separator, to a liquefiable
temperature, an expansion valve for liquefying the boil-off gas by
reducing a pressure of the boil-off gas that has been cooled down
by the heat exchanger for gas liquefaction, and a gas-liquid
separator for separating the boil-off gas, which has been liquefied
at least in part by the expansion valve, into a liquid component
and a gas component.
3. The boil-off gas recovery system according to claim 2, wherein
the heat exchanger for oil constituent condensation exchanges heat
between the boil-off gas sent from the tank to the oil supply type
compressor and the boil-off gas that has been compressed by the oil
supply type compressor.
4. The boil-off gas recovery system according to claim 2, wherein:
the reliquefying system includes a refrigerating system of a
refrigerator; the heat exchanger for oil constituent condensation
is an evaporator arranged at a circulation passage through which a
cooling medium circulates in the refrigerating system of the
refrigerator; and the evaporator evaporates the cooling medium in
the refrigerating system and cools down the boil-off gas to the
temperature equal to or lower than the condensation temperature by
exchanging heat between the cooling medium and the boil-off gas
that has been compressed by the oil supply type compressor.
5. The boil-off gas recovery system according to claim 3, wherein
the reliquefying system includes a temperature control means for
adjusting a temperature of the boil-off gas after being cooled down
by the heat exchanger for oil constituent condensation, but before
the oil constituent is separated from the boil-off gas by the
separator.
6. The boil-off gas recovery system according to claim 5, wherein
the temperature control means increases the temperature of the
boil-off gas after being cooled down by the heat exchanger for oil
constituent condensation by merging the boil-off gas before being
cooled down by the heat exchanger for oil constituent condensation
to the boil-off gas after being cooled down by the heat exchanger
for oil constituent condensation.
7. The boil-off gas recovery system according to claim 6, wherein
the temperature control means includes a bypass pipe in which a
bypass passage is formed for merging the boil-off gas before being
cooled down by the heat exchanger for oil constituent condensation
to the boil-off gas after being cooled down by the heat exchanger
for oil constituent condensation, a valve arranged at the bypass
pipe for adjusting an opening of the bypass passage, and an opening
control portion for controlling the opening of the bypass
passage.
8. The boil-off gas recovery system according to claim 1, wherein
the reliquefying system includes an oil filter for removing the oil
constituent contained in the boil-off gas before being cooled down
by the heat exchanger for oil constituent condensation.
9. The boil-off gas recovery system according to claim 4, wherein
the reliquefying system includes a temperature control means for
adjusting a temperature of the boil-off gas after being cooled down
by the heat exchanger for oil constituent condensation, but before
the oil constituent is separated from the boil-off gas by the
separator.
Description
BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to a boil-off gas recovery
system for recovering boil-off gas generated in a tank storing
liquefied gas.
Description of the Related Art
[0002] In a liquefied natural gas carrying vessel, boil-off gas is
generated in a tank storing the liquefied natural gas. Such
boil-off gas is effectively utilized as fuel for an engine, a steam
boiler, and a generator in the vessel, and/or returned to the tank
after being reliquefied. As a technique for reliquefying the
boil-off gas generated in the tank and returning it to the tank, a
boil-off gas recovery system described in JP-2015-158263 A has been
known.
[0003] In the boil-off gas recovery system described in
JP-2015-158263 A, the boil-off gas generated in the tank is
compressed by an oil supply type compressor to reliquefy a part of
the boil-off gas, and the reliquefied boil-off gas is returned to
the tank. In this process, the boil-off gas compressed by the oil
supply type compressor contains an oil constituent derived from
lubricating oil in the oil supply type compressor, thus the oil
constituent may be mixed into the tank together with the boil-off
gas. For this reason, the boil-off gas recovery system in
JP-2015-158263 A includes a filter for removing the oil constituent
contained in the boil-off gas.
[0004] However, although the boil-off gas recovery system of
JP-2015-158263 A can capture the oil constituent in a liquid state
with the filter, it fails to capture the oil constituent in a gas
state with the filter. Thus, the oil constituent contained in the
boil-off gas cannot be sufficiently removed by this system. As a
result, the boil-off gas recovery system of JP-2015-158263 A has
such a problem that the oil constituent is mixed into the tank.
SUMMARY OF THE INVENTION
[0005] The present invention has been implemented in view of the
problem described above, and an object of the present invention is
to provide a boil-off gas recovery system in which an oil
constituent is hardly mixed into a tank during recovery of boil-off
gas compressed by an oil supply type compressor.
[0006] A boil-off gas recovery system according to the present
invention includes a tank storing liquefied gas, an oil supply type
compressor for compressing boil-off gas generated by partial
evaporation of the liquefied gas in the tank, and a reliquefying
system for liquefying the boil-off gas compressed by the oil supply
type compressor and returning the liquefied gas that has been
liquefied to the tank. The reliquefying system includes a heat
exchanger for oil constituent condensation for cooling down the
boil-off gas to a temperature equal to or lower than a condensation
temperature of an oil constituent contained in the boil-off gas, a
separator for separating the oil constituent condensed by the heat
exchanger for oil constituent condensation from the boil-off gas,
and a reliquefying portion for liquefying the boil-off gas from
which the oil constituent is separated.
[0007] In this configuration, the reliquefying system includes the
heat exchanger for oil constituent condensation for cooling down
the boil-off gas to the temperature equal to or lower than the
condensation temperature of the oil constituent contained in the
boil-off gas, thus the oil constituent contained in the boil-off
gas is condensed by the heat exchanger for oil constituent
condensation. Further, the reliquefying system includes the
separator for separating the oil constituent condensed by the heat
exchanger for oil constituent condensation from the boil-off gas,
thus the oil constituent condensed by the heat exchanger for oil
constituent condensation is captured by the separator. In this
manner, the oil constituent is sufficiently removed from the
boil-off gas, thus the oil constituent is hardly mixed into the
tank in the above-mentioned boil-off gas recovery system.
[0008] In the above-mentioned configuration, the reliquefying
portion may include a heat exchanger for gas liquefaction for
cooling down the boil-off gas, from which the oil constituent has
been separated by the separator, to a liquefiable temperature, an
expansion valve for liquefying the boil-off gas by expanding the
boil-off gas cooled down by the heat exchanger for gas
liquefaction, a gas-liquid separator for separating the boil-off
gas, which has been liquefied at least in part by the expansion
valve, into a liquid component and a gas component.
[0009] In this configuration, the boil-off gas has been already
cooled down to the temperature equal to or lower than the
condensation temperature of the oil constituent by the heat
exchanger for oil constituent condensation before it is cooled down
by the heat exchanger for gas liquefaction. This can reduce a cold
amount required for liquefaction performed by the heat exchanger
for gas liquefaction. As a result, the heat exchanger for gas
liquefaction can be downsized.
[0010] In the above-mentioned configuration, the heat exchanger for
oil constituent condensation may exchange heat between the boil-off
gas sent from the tank to the oil supply type compressor and the
boil-off gas that has been compressed by the oil supply type
compressor.
[0011] In this configuration, the heat exchanger for oil
constituent condensation cools down the boil-off gas that has been
compressed by the oil supply type compressor by utilizing the
boil-off gas sent from the tank to the oil supply type compressor,
thus a separate cooling medium is not necessary for cooling the
boil-off gas that has been compressed by the oil supply type
compressor. As a result, the above-mentioned boil-off gas recovery
system can be downsized.
[0012] In the above-mentioned configuration, the reliquefying
system may include a refrigerating system of a refrigerator. The
heat exchanger for oil constituent condensation may be an
evaporator arranged at a circulation passage through which a
cooling medium circulates in the refrigerating system of the
refrigerator, and the evaporator may evaporate the cooling medium
in the refrigerating system and cool down the boil-off gas to the
temperature equal to or lower than the condensation temperature by
exchanging heat between the cooling medium and the boil-off gas
that has been compressed by the oil supply type compressor.
[0013] In this configuration, the oil constituent contained in the
boil-off gas can be efficiently condensed by the refrigerator. This
is because the condensation temperature of the oil constituent
contained in the boil-off gas is close to the cooling temperature
of the refrigerator, which prevents the oil constituent from being
solidified, but not being condensed.
[0014] In the above-mentioned configuration, the reliquefying
system may include a temperature control means for adjusting a
temperature of the boil-off gas after being cooled down by the heat
exchanger for oil constituent condensation, but before the oil
constituent is separated from the boil-off gas by the
separator.
[0015] This configuration makes it easy to adjust the temperature
of the boil-off gas cooled down by the heat exchanger for oil
constituent condensation to a suitable temperature, for example,
the temperature equal to or lower than the condensation
temperature.
[0016] In the above-mentioned configuration, the temperature
control means preferably increases the temperature of the boil-off
gas after being cooled down by the heat exchanger for oil
constituent condensation by merging the boil-off gas before being
cooled down by the heat exchanger for oil constituent condensation
to the boil-off gas after being cooled down by the heat exchanger
for oil constituent condensation.
[0017] When the temperature of the boil-off gas cooled down by the
heat exchanger for oil constituent condensation is reduced to a
freezing point or lower of the oil constituent, the oil constituent
may be solidified to clog a pipe. However, according to the
above-mentioned configuration, the temperature control means
increases the temperature of the boil-off gas after being cooled
down by the heat exchanger for oil constituent condensation by
utilizing the boil-off gas before being cooled down by the heat
exchanger for oil constituent condensation, thereby preventing the
clogging of the pipe caused by solidification of the oil
constituent.
[0018] In the above-mentioned configuration, the temperature
control means may include a bypass pipe in which a bypass passage
is formed for merging the boil-off gas before being cooled by the
heat exchanger for oil constituent condensation to the boil-off gas
after being cooled by the heat exchanger for oil constituent
condensation, a valve arranged on the bypass pipe for adjusting an
opening of the bypass passage, and an opening control portion for
controlling the opening of the bypass passage.
[0019] In this configuration, the temperature control means can be
achieved by a simply configuration that includes the bypass pipe,
the valve, and the opening control portion.
[0020] In the above-mentioned configuration, the reliquefying
system may include an oil filter for removing the oil constituent
contained in the boil-off gas before being cooled down by the heat
exchanger for oil constituent condensation.
[0021] In this configuration, the oil constituent in a liquid state
contained in the boil-off gas is removed by the oil filter, thereby
enabling to reduce a risk that a heat transfer is impaired by the
oil constituent in a liquid state in the heat exchanger for oil
constituent condensation. As a result, the heat exchanger for oil
constituent condensation can be downsized.
[0022] According to the present invention, the oil constituent is
hardly mixed into the tank when the boil-off gas compressed by the
oil supply type compressor is reliquefied.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a schematic block diagram illustrating a boil-off
gas recovery system according to a first embodiment.
[0024] FIG. 2 is a schematic block diagram illustrating a
reliquefying system of the boil-off gas recovery system according
to the first embodiment.
[0025] FIG. 3 is a longitudinal section view of a first separator
of the boil-off gas recovery system according to the first
embodiment.
[0026] FIG. 4 is a schematic block diagram illustrating a
reliquefying system of a boil-off gas recovery system according to
a second embodiment.
[0027] FIG. 5 is a schematic block diagram illustrating a
refrigerating system of a refrigerator using an evaporator that is
applied to a heat exchanger for oil constituent condensation of the
boil-off gas recovery system according to the second
embodiment.
[0028] FIG. 6 is a schematic block diagram illustrating a heat
exchanger for oil constituent condensation of a boil-off gas
recovery system according to a third embodiment.
[0029] FIG. 7 is a schematic block diagram illustrating a
refrigerating system of a refrigerator using an evaporator that is
applied to a heat exchanger for oil constituent condensation of a
boil-off gas recovery system according to a fourth embodiment.
[0030] FIG. 8 is a schematic block diagram illustrating a boil-off
gas recovery system according to a fifth embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] Hereinafter, embodiments of the present invention will be
described with reference to the drawings. Note that, for
convenience of explanation, the drawings referred to hereinafter
show only principal constituent elements, necessary for describing
the boil-off gas recovery system according to the embodiments of
the present invention, in a simplified manner. Thus, the boil-off
gas recovery system according to the embodiments of the present
invention may include any constituent elements that are not
illustrated in the drawings referred to in the present
specification.
[0032] FIG. 1 is a schematic block diagram illustrating a boil-off
gas recovery system 1 according to a first embodiment. FIG. 2 is a
schematic block diagram illustrating a reliquefying system 9 of the
boil-off gas recovery system 1 according to the first embodiment.
The boil-off gas recovery system 1 is installed in a vessel that
carries liquefied gas such as liquefied natural gas. The boil-off
gas recovery system 1 includes a tank 2, a compressor 3, a first
pipe 4, a second pipe 5, an engine 6, a gas combustion apparatus 7,
a generator 8, and a reliquefying system 9.
[0033] The tank 2 stores liquefied natural gas at about
-160.degree. C. The tank 2 may store liquefied petroleum gas
instead of the liquefied natural gas.
[0034] The compressor 3 with five compression stages includes
non-oil supply type compressors 3a requiring no lubricating oil and
oil supply type compressors 3b requiring lubricating oil. The
non-oil supply type compressors 3a are arranged at a first and
second stages. The oil supply type compressors 3b are arranged at a
third, fourth and fifth stages. Note that the compression stages of
the compressors 3 are not limited to five stages and may include
any number of stages as long as the oil supply type compressor 3b
is included.
[0035] The first pipe 4 connects the tank 2 and the compressors 3
via the reliquefying system 9. The first pipe 4 transfers the
boil-off gas generated by evaporation of the liquefied natural gas
stored in the tank 2 from the tank 2 to the compressors 3.
[0036] The second pipe 5 connects the compressors 3 and the engine
6. The second pipe 5 is branched on its way to connect the
compressors 3, the gas combustion apparatus 7, and the generator
8.
[0037] The engine 6 is supplied with the boil-off gas compressed by
the compressors 3 via the second pipe 5. In this configuration, the
vessel can combust the boil-off gas in the engine 6 to generate a
driving force.
[0038] The gas combustion apparatus 7 is an apparatus that safely
treats the excess boil-off gas by combustion when the production of
the boil-off gas exceeds an amount necessary as the fuel for the
engine 6 and the generator 8. The gas combustion apparatus 7 is
supplied with the boil-off gas compressed by the compressors 3 via
the second pipe 5.
[0039] The generator 8 is supplied with the boil-off gas compressed
by the compressors 3 via the second pipe 5. In this configuration,
the generator 8 generates power required for driving various
apparatuses of the vessel using the supplied boil-off gas as the
fuel.
[0040] The reliquefying system 9 will be described with reference
to FIGS. 1 and 2. The reliquefying system 9 includes a third pipe
10, an oil filter 40, a heat exchanger for oil constituent
condensation 11, a temperature control means 12, a fourth pipe 13,
a first separator 14, a fifth pipe 15, a heat exchanger for gas
liquefaction 16, a sixth pipe 17, an expansion valve 18, a
gas-liquid separator 19, a seventh pipe 20, and an eighth pipe 21.
A reliquefying portion is constituted by the heat exchanger for gas
liquefaction 16, the expansion valve 18, and the gas-liquid
separator 19.
[0041] The third pipe 10 connects a point between the oil supply
type compressor 3b at the fourth stage and the oil supply type
compressor 3b at the fifth stage to the heat exchanger for oil
constituent condensation 11. The third pipe 10 transfers the
boil-off gas compressed by the compressors 3 from the first stage
to the fourth stage to the heat exchanger for oil constituent
condensation 11. Note that the third pipe 10 is not limited to the
one branched from the point between the compressor 3b at the fourth
stage and the compressor 3b at the fifth stage, and it may be
branched at any downstream location of the oil supply type
compressor 3b. The boil-off gas compressed by the compressors 3
from the first stage to the fourth stage is cooled down to a
temperature of, for example, 20.degree. C. to 45.degree. C., by a
gas cooler (not illustrated). The third pipe 10 is provided with a
first control valve 22. The first control valve 22 can adjust an
opening of the passage of the third pipe 10. The first control
valve 22 adjusts flow rates of the boil-off gas compressed by the
compressors 3 flowing into the second pipe 5 and the third pipe 10
between the second pipe 5 and the third pipe 10. The third pipe 10
is provided with an oil filter 40. The oil filter 40 removes the
oil constituent in a liquid state contained in the boil-off gas
compressed by the compressors 3.
[0042] The heat exchanger for oil constituent condensation 11 cools
down the boil-off gas compressed by the compressors 3 to a
condensation temperature (e.g., 0.degree. C.) of the oil
constituent contained in the boil-off gas. The heat exchanger for
oil constituent condensation 11 may cool down the boil-off gas to
the condensation temperature (e.g., 0.degree. C.) of the oil
constituent or lower. The cooling temperature of the boil-off gas
by the heat exchanger for oil constituent condensation 11 is
appropriately set according to the lubricating oil used in the oil
supply type compressors 3b. The heat exchanger for oil constituent
condensation 11 includes a low temperature side passage 11a through
which the boil-off gas sent from the tank 2 to the compressors 3
passes and a high temperature side passage 11b through which the
boil-off gas compressed by the compressors 3 passes. The heat
exchanger for oil constituent condensation 11 exchanges heat
between the boil-off gas sent from the tank 2 to the compressors 3
and the boil-off gas compressed by the compressors 3. In this
process, the oil constituent contained in the boil-off gas is
condensed. The boil-off gas passing through the low temperature
side passage 11a is heated, for example, from -50.degree. C. to
20.degree. C. The low temperature side passage 11a is connected to
the first pipe 4. An inlet of the high temperature side passage 11b
is connected to the third pipe 10. An outlet of the high
temperature side passage 11b is connected to the fourth pipe
13.
[0043] The temperature control means 12 adjusts a temperature of
the boil-off gas that has been cooled down by passing through the
high temperature side passage 11b of the heat exchanger for oil
constituent condensation 11 to a set temperature. The set
temperature may be set, for example, to be equal to or lower than
the condensation temperature (e.g., 0.degree. C.) of the oil
constituent contained in the boil-off gas, and higher than a
solidification temperature (e.g., -25.degree. C.) of the oil
constituent. The temperature control means 12 includes a bypass
pipe 12a connecting the third pipe 10 and the fourth pipe 13, a
second control valve 12b arranged on the bypass pipe 12a, a
temperature sensor 12c arranged on the fourth pipe 13, and a
control portion 12d controlling the second control valve 12b. The
temperature sensor 12c and the control portion 12d constitute an
opening control portion.
[0044] The bypass pipe 12a in which a bypass passage is formed
merges the boil-off gas before being cooled down by the heat
exchanger for oil constituent condensation 11 to the boil-off gas
after being cooled by the heat exchanger for oil constituent
condensation 11. The second control valve 12b can adjust an opening
of the bypass passage. The second control valve 12b adjusts a flow
rate of the boil-off gas compressed by the compressors 3 flowing
into the bypass pipe 12a. The temperature sensor 12c detect a
temperature of the boil-off gas flowing through the fourth pipe 13
and sends a signal corresponding to the temperature to the control
portion 12d. The control portion 12d sends a signal for controlling
the opening of the bypass passage based on the signal from the
temperature sensor 12c to the second control valve 12b. For
example, when the control portion 12d determines that the
temperature of the boil-off gas that has been cooled down by the
heat exchanger for oil constituent condensation 11 becomes lower
than the set temperature based on the signal from the temperature
sensor 12c, the control portion 12d sends an operation command for
opening the bypass passage to the second control valve 12b. The
second control valve 12b opens the bypass passage upon receipt of
the operation command. In this manner, the boil-off gas before
being cooled down by the heat exchanger for oil constituent
condensation 11 flows through the bypass passage and merges to the
boil-off gas after being cooled down by the heat exchanger for oil
constituent condensation 11. As a result, the temperature of the
boil-off gas after being cooled by the heat exchanger for oil
constituent condensation 11 increases, thereby preventing the
clogging of the fourth pipe 13 caused by the solidification of the
oil constituent.
[0045] Conversely, when the control portion 12d determines that the
temperature of the boil-off gas that has been cooled down by the
heat exchanger for oil constituent condensation 11 becomes higher
than the set temperature (e.g., 0.degree. C.) based on the signal
from the temperature sensor 12c, the control portion 12d sends an
operation command for closing the bypass passage to the second
control valve 12b. The second control valve 12b closes the bypass
passage upon receipt of the operation command. In this manner, the
boil-off gas before being cooled down by the heat exchanger for oil
constituent condensation 11 is prevented from flowing through the
bypass passage and the whole amount of such boil-off gas is cooled
down by the heat exchanger for oil constituent condensation 11,
thus the temperature of the boil-off gas after being cooled down by
the heat exchanger for oil constituent condensation 11 decreases.
In this manner, the temperature control means 12 adjusts the
temperature of the boil-off gas after being cooled down by the heat
exchanger for oil constituent condensation 11 to the set
temperature (e.g., 0.degree. C.).
[0046] The fourth pipe 13 connects the heat exchanger for oil
constituent condensation 11 and the first separator 14. The fourth
pipe 13 transfers the boil-off gas cooled down to the set
temperature (e.g., 0.degree. C.) by the heat exchanger for oil
constituent condensation 11 to the first separator 14.
[0047] FIG. 3 is a longitudinal section view of the first separator
14 of the exemplary boil-off gas recovery system 1. The first
separator 14 includes a capturing portion 23 for capturing the oil
constituent and a level sensor 24 for detecting a capture amount of
the oil constituent.
[0048] The capturing portion 23 includes a main body portion 25 of
a cylindrical shape with both ends closed, a small-diameter portion
26 of a cylindrical shape with a diameter smaller than the main
body portion 25, a gas inlet pipe 27 for allowing the boil-off gas
to flow into the small-diameter portion 26, and a gas outlet pipe
28 for flowing out the boil-off gas to an outside. The
small-diameter portion 26 is arranged coaxially with the main body
portion 25 in the main body portion 25 and installed on a lower
surface of an upper end portion 25a of the main body portion 25. An
outer surface of the small-diameter portion 26 is constituted by a
mesh. Thus, the boil-off gas and the oil constituent condensed by
the heat exchanger for oil constituent condensation 11 can pass
through the mesh. The gas inlet pipe 27 is installed on an upper
surface of the upper end portion 25a of the main body portion 25.
The gas inlet pipe 27 is connected to the fourth pipe 13. The gas
inlet pipe 27 forms an inlet side passage 27a through which the
boil-off gas passes. The inlet side passage 27a communicates with
an inside of the small-diameter portion 26. The gas outlet pipe 28
is arranged on a side surface of the main body portion 25. The gas
outlet pipe 28 is connected to the fifth pipe 15. In this
configuration, the boil-off gas having passed through the mesh has
a specific gravity smaller than that of the air, thus it passes
through the inside of the main body portion 25 and flows out to the
fifth pipe 15 via the gas outlet pipe 28. On the other hand, the
oil constituent in a liquid state having passed through the mesh
has a specific gravity larger than that of the air, thus it is
accumulated on a bottom 25b of the main body portion 25. In this
manner, the capturing portion 23 separates the oil constituent
condensed by the heat exchanger for oil constituent condensation 11
from the boil-off gas.
[0049] The level sensor 24 determines whether a liquid level of the
oil constituent accumulated on the bottom 25b of the main body
portion 25 exceeds a predetermined value. When the level sensor 24
determines that the liquid level of the oil constituent accumulated
on the bottom 25b of the main body portion 25 exceeds the
predetermined value, the level sensor 24 can sound an alarm to
notify a worker that the first separator 14 requires a maintenance
inspection. Note that the first separator 14 is not limited as long
as it can separate the oil constituent condensed by the heat
exchanger for oil constituent condensation 11 from the boil-off
gas. The first separator 14 may be, for example, an activated
carbon filter.
[0050] With reference to FIG. 2, the fifth pipe 15 connects the gas
outlet pipe 28 of the first separator 14 and the heat exchanger for
gas liquefaction 16. The fifth pipe 15 transfers the boil-off gas
from which the oil constituent is separated by the first separator
14 to the heat exchanger for gas liquefaction 16.
[0051] The heat exchanger for gas liquefaction 16 cools down the
boil-off gas from which the oil constituent is separated by the
first separator 14 to a liquefiable temperature (e.g., -100.degree.
C.) using the expansion valve 18. The heat exchanger for gas
liquefaction 16 includes a low temperature side passage 16a through
which the boil-off gas sent from the tank 2 to the compressors 3
passes and a high temperature side passage 16b through which the
boil-off gas from which the oil constituent is separated by the
first separator 14 passes. The heat exchanger for gas liquefaction
16 exchanges heat between the boil-off gas sent from the tank 2 to
the compressors 3 and the boil-off gas from which the oil
constituent is separated by the first separator 14. In this
process, the boil-off gas passing through the low temperature side
passage 16a is heated, for example, from -160.degree. C. to
-50.degree. C. The low temperature side passage 16a is connected to
the first pipe 4. An inlet of the high temperature side passage 16b
is connected to the fifth pipe 15. An outlet of the high
temperature side passage 16b is connected to the sixth pipe 17.
[0052] The sixth pipe 17 connects the heat exchanger for gas
liquefaction 16 and the gas-liquid separator 19. The sixth pipe 17
transfers the boil-off gas cooled down by the heat exchanger for
gas liquefaction 16 to the gas-liquid separator 19.
[0053] The expansion valve 18 is arranged on the sixth pipe 17. The
expansion valve 18 expands the boil-off gas cooled down by the heat
exchanger for gas liquefaction 16 to reduce its pressure. In this
process, a boiling point of the boil-off gas decreases and at least
a part of the boil-off gas is liquefied. As a result, the boil-off
gas is turned into a gas-liquid two phase state.
[0054] The gas-liquid separator 19 separates the boil-off gas,
which is turned into the gas-liquid two phase state by the
expansion valve 18, into a liquid component and a gas component.
The gas-liquid separator 19 is connected to the seventh pipe 20 and
the eighth pipe 21.
[0055] The seventh pipe 20 connects the gas-liquid separator 19 and
the tank 2. The seventh pipe 20 transfers the liquid component of
the boil-off gas separated by the gas-liquid separator 19 to the
tank 2. In this manner, the boil-off gas generated in the tank 2 is
returned to the tank 2 as the liquid component.
[0056] The eighth pipe 21 connects the gas-liquid separator 19 and
the first pipe 4. The eighth pipe 21 further connects the
gas-liquid separator 19 and the gas combustion apparatus 7. The
eighth pipe 21 transfers the gas component of the boil-off gas
separated by the gas-liquid separator 19 to the first pipe 4 and
the gas combustion apparatus 7. The eighth pipe 21 is provided with
a third control valve 29 and a fourth control valve 30. The third
control valve 29 and the fourth control valve 30 can adjust
openings of passages of the boil-off gas. This configuration
enables to adjust flow rates of the boil-off gas flowing into the
first pipe 4 and the gas combustion apparatus 7.
[0057] According to the boil-off gas recovery system 1 of the first
embodiment, the boil-off gas is compressed by the oil supply type
compressors 3b, thus the boil-off gas contains the oil constituent
of the lubricating oil from the oil supply type compressors 3b.
[0058] However, the oil constituent contained in the boil-off gas
is condensed by being cooled down to the set temperature (e.g.,
0.degree. C.) by the heat exchanger for oil constituent
condensation 11 and separated from the boil-off gas by the first
separator 14. Thus, the oil constituent is hardly mixed into the
tank 2 in the boil-off gas recovery system 1.
[0059] FIG. 4 is a schematic block diagram illustrating an
exemplary reliquefying system 38 of a boil-off gas recovery system
according to a second embodiment. FIG. 5 is a schematic block
diagram illustrating a refrigerating system 32 of a refrigerator
using an evaporator 33a that is applied to a heat exchanger for oil
constituent condensation 33 of the boil-off gas recovery system
according to the second embodiment. The boil-off gas recovery
system of the second embodiment is different from the heat
exchanger for oil constituent condensation 11 of the first
embodiment in that the evaporator 33a in the refrigerating system
32 of the refrigerator is used as the heat exchanger for oil
constituent condensation 33 for cooling down the boil-off gas
compressed by the compressors 3 to the set temperature (e.g.,
0.degree. C.). In other respects, the boil-off gas recovery system
of the second embodiment has the same configurations as that of the
first embodiment. The same configurations as used in the first
embodiment are designated by the same reference signs as used in
the first embodiment and description thereof is omitted.
[0060] The reliquefying system 38 includes the refrigerating system
32 of the refrigerator. The heat exchanger for oil constituent
condensation 33 is the evaporator 33a that is arranged on a
circulation passage 34, through which a cooling medium is
circulated, in the refrigerating system 32 of the refrigerator.
[0061] The refrigerating system 32 of the refrigerator includes a
compressor 35 for compressing the cooling medium flowing through
the circulation passage 34, a condenser 36 for exchanging heat
between the cooling medium and an exhaust heat-treated medium such
as outside air and cooling water, an expansion valve 37 for
expanding the cooling medium liquefied by the condenser 36, and the
evaporator 33a for exchanging heat between the liquefied cooling
medium expanded by the expansion valve 37 and the boil-off gas
compressed by the compressors 3.
[0062] The evaporator 33a evaporates the liquefied cooling medium
by exchanging heat between the liquefied cooling medium expanded by
the expansion valve 37 and the boil-off gas compressed by the
compressors 3. In this process, the boil-off gas is deprived of
heat by the cooling medium and thus cooled down to the set
temperature (e.g., 0.degree. C.) to condense the oil constituent
contained in the boil-off gas. A cooling temperature of the
boil-off gas in the evaporator 33a is adjusted to the set
temperature (e.g., 0.degree. C.) by adjusting a rotation speed of a
pump for circulating the cooling medium (not illustrated) and a
rotation speed of the compressor 35, by employing the temperature
control means 12 similar to the one used in the first embodiment,
or the like.
[0063] In the boil-off gas cooled down to the set temperature
(e.g., 0.degree. C.) by the evaporator 33a, the condensed oil
constituent is separated from the boil-off gas by the first
separator 14 in the same manner as in the first embodiment.
[0064] FIG. 6 is a schematic block diagram illustrating a heat
exchanger for oil constituent condensation 39 of a boil-off gas
recovery system according to a third embodiment. In the boil-off
gas recovery system according to the third embodiment, the heat
exchanger for oil constituent condensation 39 for cooling down the
boil-off gas compressed by the compressors 3 to the set temperature
(e.g., 0.degree. C.) is different from the heat exchanger for oil
constituent condensation 11 of the first embodiment. In other
configurations, the boil-off gas recovery system according to the
third embodiment has the same configurations as that of the first
embodiment. The same configurations as used in the first embodiment
are designated by the same reference signs as used in the first
embodiment and description thereof is omitted. In the heat
exchanger for oil constituent condensation 11 of the first
embodiment, the boil-off gas transferred from the tank 2 to the
compressors 3 is used as the cooling medium for cooling down the
boil-off gas compressed by the compressors 3. On the other hand, in
the heat exchanger for oil constituent condensation 39 of the third
embodiment, the cooing water is used as a medium for cooling down
the boil-off gas compressed by the compressors 3. Thus, the
boil-off gas recovery system of the third embodiment is configured
in a very simple manner.
[0065] FIG. 7 is a schematic block diagram illustrating a
refrigerating system 42 of a refrigerator using an evaporator 41a,
which is applied to a heat exchanger for oil constituent
condensation 41 of a boil-off gas recovery system according to a
fourth embodiment. In the boil-off gas recovery system according to
the fourth embodiment, the heat exchanger for oil constituent
condensation 41 for cooling down the boil-off gas compressed by the
compressors 3 to the set temperature (e.g., 0.degree. C.) is
different from the heat exchanger for oil constituent condensation
11 of the first embodiment. In other configurations, the boil-off
gas recovery system according to the fourth embodiment has the same
configurations as that of the first embodiment. The same
configurations as used in the first embodiment are designated by
the same reference signs as used in the first embodiment and
description thereof is omitted. The heat exchanger for oil
constituent condensation 41 of the boil-off gas recovery system
according to the fourth embodiment is applied with the evaporator
41a of the refrigerating system 42, which is a modification of the
refrigerating system 32 of the second embodiment (see FIG. 5).
[0066] The refrigerating system 42 includes a compressor 43, a gas
cooler 44, a second separator 45, an oil cooler 46, an expansion
valve 47, an evaporator 41a, and a deflation valve 49. The
compressor 43, the gas cooler 44, the second separator 45, the
expansion valve 47, the evaporator 41a, and the deflation valve 49
are arranged in this order on a circulation passage 50 of a cooling
medium.
[0067] The compressor 43 compresses the cooling medium flowing
through the circulation passage 50. The gas cooler 44 cools down
the cooling medium compressed by the compressor 43. The second
separator 45 separates the cooling medium into a liquid component
and a gas component. The liquid component of the cooling medium is
cooled down by the oil cooler 46 and returned to the compressor 43.
The expansion valve 47 expands the gas component of the cooling
medium for liquefaction. The evaporator 41a exchanges heat between
the cooling medium liquefied by the expansion valve 47 and the
boil-off gas compressed by the compressors 3 to evaporates the
liquefied cooling medium and condense the oil constituent contained
in the boil-off gas. The evaporator 41a has the same function as
the evaporator 33a of the second embodiment (see FIG. 5). The
deflation valve 49 deflates the cooling medium evaporated by the
evaporator 41a.
[0068] FIG. 8 is a schematic block diagram illustrating a boil-off
gas recovery system 51 according to a fifth embodiment. The
boil-off gas recovery system 51 according to the fifth embodiment
is different from those of the first and second embodiments in that
oil supply type compressors 52 are arranged at a first and second
stages and that a reliquefying system 55 includes non-oil supply
type compressors 53. In other respects, the boil-off gas recovery
system 51 of the fifth embodiment has the same configurations as
those of the first and second embodiments. The same configurations
as used in the first and second embodiments are designated by the
same reference signs as used in the first and second embodiments
and description thereof is omitted.
[0069] The boil-off gas recovery system 51 according to the fifth
embodiment includes the oil supply type compressors 52 at two
stages instead of the compressors 3 of the first embodiment. The
boil-off gas recovery system 51 according to the fifth embodiment
further includes a gas cooler 54 for cooling down the boil-off gas
compressed by the oil supply type compressors 52, in addition to
the configurations of the first embodiment. The oil supply type
compressor 52 at the first stage is connected to the first pipe 4.
The oil supply type compressor 52 at the second stage is connected
to the third pipe 10.
[0070] A reliquefying system 55 of the fifth embodiment is
constituted by adding the non-oil supply type compressors 53 at
three stages to the reliquefying system 38 of the second embodiment
(see FIG. 5). The non-oil supply type compressors 53 at three
stages are arranged between the first separator 14 and the heat
exchanger for gas liquefaction 16. The non-oil supply type
compressors 53 at three stages are provided to increase efficiency
of reliquefaction of the boil-off gas by the expansion valve
18.
[0071] In the boil-off gas recovery system 51 of the fifth
embodiment, the oil constituent contained in the boil-off gas is
separated by the first separator 14 in the same manner as in the
first embodiment, thus the oil constituent is hardly mixed into the
tank 2.
[0072] The temperature control means 12 of the first embodiment
described above is arranged on the third pipe 10, however, it may
be arranged on the first pipe 4 or on both of the third pipe 10 and
the first pipe 4. Note that constituent elements having the same
functions as the temperature control means 12 of the first
embodiment described above are designated by the same reference
signs as used in the first embodiment described above and
description thereof is simplified. The temperature control means 12
of this modification includes the bypass pipe 12a that connects a
point between the heat exchanger for gas liquefaction 16 and the
heat exchanger for oil constituent condensation 11 of the first
pipe 4, and a downstream side of the heat exchanger for oil
constituent condensation 11 of the first pipe 4, the second control
valve 12b arranged on the bypass pipe 12a, the temperature sensor
12c arranged at a downstream side of the heat exchanger for oil
constituent condensation 11 of the first pipe 4, and the control
portion 12d controlling the second control valve 12b.
[0073] The temperature control means 12 of the modification adjusts
a temperature of the boil-off gas that has been heated by passing
through the low temperature side passage 11a of the heat exchanger
for oil constituent condensation 11 to a set temperature (e.g.,
20.degree. C.). The temperature control means 12 of the
modification adjusts the temperature of the boil-off gas in the
same manner as in the first embodiment described above.
Specifically, when the temperature of the boil-off gas that has
been heated by passing through the low temperature side passage 11a
of the heat exchanger for oil constituent condensation 11 becomes
higher than the set temperature, the temperature control means 12
of the modification opens the second control valve 12b to merge the
boil-off gas before being heated by passing through the low
temperature side passage 11a of the heat exchanger for oil
constituent condensation 11 to the boil-off gas that has been
heated by passing through the low temperature side passage 11a of
the heat exchanger for oil constituent condensation 11. This lowers
the temperature of the boil-off gas that has been heated by passing
through the low temperature side passage 11a of the heat exchanger
for oil constituent condensation 11.
[0074] Conversely, when the temperature of the boil-off gas that
has been heated by passing through the low temperature side passage
11a of the heat exchanger for oil constituent condensation 11
becomes lower than the set temperature, the temperature control
means 12 of the modification closes the second control valve 12b.
In this manner, the temperature control means 12 of the
modification adjusts the temperature of the boil-off gas after been
heated by passing through the low temperature side passage 11a of
the heat exchanger for oil constituent condensation 11 to the set
temperature (e.g., 20.degree. C.).
[0075] The temperature control means 12 of the modification adjusts
in advance the temperature of the boil-off gas after been heated by
passing through the low temperature side passage 11a of the heat
exchanger for oil constituent condensation 11 to the set
temperature (e.g., 20.degree. C.), thereby making constant a
temperature of the boil-off gas that has been compressed by the
compressors 3 and flows into the high temperature side passage 11b
of the heat exchanger for oil constituent condensation 11. In this
manner, the oil constituent contained in the boil-off gas
compressed by the compressors 3 can be effectively condensed by the
heat exchanger for oil constituent condensation 11.
* * * * *