JP6524485B2 - Boil off gas utilization system - Google Patents

Description

  The present invention relates to a boil-off gas utilization system that uses boil-off gas in an LNG carrier that carries liquefied natural gas (LNG).

  In the LNG carrier, a boil-off gas in which the liquefied natural gas is naturally vaporized is generated in the LNG tank storing the liquefied natural gas. If the boil-off gas is left as it is, the internal pressure of the LNG tank rises, so it is necessary to suppress the increase of the internal pressure of the LNG tank by using or processing the boil-off gas. For example, steam is generated by boil-off gas, the turbine is driven by steam, the propeller is rotated by the turbine, and used as propulsion, or the generator is driven by the turbine, and the propeller is rotated by the electric motor. It is used as a driving force.

  In addition, the boil-off gas is compressed to a high pressure fluid, and the high pressure fluid is injected into the combustion chamber of the diesel engine for combustion to drive a low speed diesel engine, and the low speed diesel engine rotates a propeller for propulsion and It is also tried to do. On the other hand, when the demand for fuel is low, high pressure fluid is also liquefied and returned to the LNG tank.

  In order to make a low pressure fluid such as boil off gas a high pressure fluid, the boil off gas is compressed using a multistage compressor. The multistage compressor includes, for example, a plurality of compressors connected in series as shown in Patent Document 1.

  Generally, the compressor is controlled to keep its discharge pressure constant. For example, using a spillback pipe provided with a spillback valve in a pipe connected from the outlet side to the inlet side of the compressor, the fluid discharged from the outlet side of the compressor when the discharge pressure becomes higher than the reference value It is carried out to keep discharge pressure below a reference value by returning to the inlet side of a compressor by spill back piping (for example, patent documents 2).

Unexamined-Japanese-Patent No. 8-219088 gazette JP, 2011-226418, A

  In ships such as LNG carriers, the demand for fuel for propulsion engines fluctuates affected by weather, ocean currents, waves and maneuvers. For this reason, when boil off gas is compressed and used for a diesel engine of an LNG ship, the pressure of the compressed boil off gas may increase excessively if the compression amount of the boil off gas is not adjusted according to the demand. In addition, there are cases where the fuel for the propulsion engine may be switched from boil-off gas to another fuel such as heavy oil because of operational requirements, and in this case, the demand for boil-off gas is zero. Even in this case, in order to resume the use of the boil off gas in a short time, the compressor may stand by without stopping. In order to cope with such a case, it is conceivable to return the compressed boil-off gas to the upstream side, or liquefy the compressed boil-off gas to return it to the LNG tank.

  In a boil-off gas compressed by an oil-supply compressor using a lubricating oil, the lubricating oil mixes with the boil-off gas. Therefore, when the boil-off gas compressed by the oil-feed compressor is returned to the upstream side, the lubricating oil There is a risk that the liquefied natural gas inside will be contaminated. Therefore, it is conceivable to compress the boil-off gas with an oil-free compressor that does not use lubricating oil. Oil-free compressors use a non-contact seal, such as a labyrinth seal, between the rotating shaft and the fixed part, for example, and use a non-lubricated oil by raising the amount of discharge of the compressor beyond the reverse flow rate of fluid from the gap. Compression is possible.

  By the way, in recent years, in order to increase the output of a low-speed diesel engine, it has been attempted to inject fuel into the combustion chamber after making the pressure as high as 30 MPa or more. However, it is difficult to compress the fluid to a high pressure of 30 MPa or more in an oilless compressor. When using a refueling compressor, the fluid can be compressed to a high pressure of 30 MPa or more. On the other hand, in the oil-filling compressor, as described above, since the lubricating oil is mixed in the boil-off gas, if the compressed boil-off gas is returned to the upstream side, the liquefied natural gas in the LNG tank may be contaminated by the lubricating oil. There is. Even when using an oil-free compressor on the upstream side and using an oil-filling compressor on the downstream side, if the boil-off gas is returned from the downstream side to the upstream side of the oil-filling compressor using spillback piping, no Since a slight backflow occurs in a refueling compressor, lubricating oil may contaminate liquefied natural gas in the LNG tank. In particular, even in a non-oiling type compressor, when the boil-off gas is returned from the downstream side to the upstream side of the compressor using spillback piping, the possibility that the liquefied natural gas in the LNG tank may be contaminated is increased.

  An object of the present invention is to use boil-off gas compressed at high pressure with a refueling compressor and to prevent contamination of liquefied natural gas in an LNG tank with lubricating oil mixed in boil-off gas. It is providing a gas utilization system.

In order to solve the above problems, according to a first aspect of the present invention, there is provided a boil-off gas utilization system for an LNG carrier carrying liquefied natural gas, the LNG carrier comprising:
LNG tank for storing liquefied natural gas,
A propulsion engine that uses, as a fuel, boil-off gas vaporized in the LNG tank;
A multi-stage compressor for compressing the boil-off gas and transferring it to the propulsion engine;
The multistage compressor is
An upstream oilless compressor for compressing the boil-off gas, and a downstream side downstream of the upstream oilless compressor for further compressing the boil-off gas compressed by the upstream oilless compressor A plurality of oilless compressors , including an oilless compressor;
One or more oiling compressors that further compress the boil-off gas compressed by the non-oiling compressor and supply it to the propulsion engine;
A first non-return provided between the plurality of oilless compressors and the oiling compressor, for preventing the backflow of the compressed gas supplied to the oiling compressor to the oilless compressor Equipped with a valve ,
The LNG carrier further comprises
Bleed piping for extracting compressed gas in which boil-off gas is compressed by the upstream oilless compressor from the upstream of the downstream oilless compressor;
A gas processing system for processing compressed gas supplied from the bleed pipe;
The compressed gas compressed by the downstream oilless compressor from the outlet side of the downstream oilless compressor and the first check valve, the inlet side of the downstream oilless compressor A third spillback pipe for returning the pipe connecting between the upstream oilless compressor and the downstream oilless compressor downstream of the bleed point where the bleed pipe branches off; ,
And the like.
At this time, the LNG carrier includes a bleed pipe adjustment valve provided to the bleed pipe,
The compressed gas supplied to the gas processing system by adjusting the degree of opening of the bleed pipe adjusting valve based on the pressure of the boil-off gas before being compressed by the non-oiling compressor vaporized from the LNG tank. It is preferable to adjust the flow rate of
Further, according to a second aspect of the present invention, there is provided a boil-off gas utilization system for an LNG carrier carrying liquefied natural gas, the LNG carrier comprising:
LNG tank for storing liquefied natural gas,
A propulsion engine that uses, as a fuel, boil-off gas vaporized in the LNG tank;
A multi-stage compressor for compressing the boil-off gas and transferring it to the propulsion engine;
The multistage compressor is
One or more oilless compressors that compress the boil-off gas;
One or more oiling compressors that further compress the boil-off gas compressed by the non-oiling compressor and supply it to the propulsion engine;
A first check valve provided between the oilless compressor and the oiling compressor, for preventing the backflow of the compressed gas supplied to the oiling compressor to the oilless compressor; , And
The LNG carrier further comprises
Boiling piping that bleeds compressed gas in which boil-off gas is compressed by at least one upstream oilless compressor among the oilless compressors from upstream of the first check valve;
A gas processing system for processing compressed gas supplied from the bleed pipe;
A bleed pipe adjustment valve provided in the bleed pipe;
The compressed gas supplied to the gas processing system by adjusting the degree of opening of the bleed pipe adjusting valve based on the pressure of the boil-off gas before being compressed by the non-oiling compressor vaporized from the LNG tank. Adjust the flow rate of

The LNG carrier is
A flow control valve for adjusting the flow rate of the boil-off gas supplied to the propulsion engine, between the propulsion engine and the refueling compressor;
First spillback piping for returning the compressed gas compressed by the oil supply compressor from between the outlet of the oil supply compressor and the flow control valve to the upstream side of the oil supply compressor;
A first spillback valve, provided in the first spillback pipe, for adjusting the flow rate of the compressed gas to be returned to the upstream side of the oil type compressor;
Decompression piping which branches from the downstream side of the oil supply compressor, decompresses the boil-off gas to a pressure that can be used by the gas processing system, and supplies the boil off gas to the gas processing system;
A pressure reducing pipe adjusting valve provided in the pressure reducing pipe, for adjusting the flow rate of the boil-off gas flowing from the pressure reducing pipe to the side of the gas processing system;
When the deviation amount of the pressure of the boil off gas from the target pressure before the boil off gas is extracted to the pressure reducing pipe after compression of the boil off gas by the oil supply compressor is equal to or less than a predetermined value, Control is performed to adjust the opening degree of the first spillback valve while maintaining the opening degree, and when the deviation amount exceeds the predetermined value, the opening degrees of the first spillback valve and the pressure reducing pipe adjustment valve A pressure control unit that performs adjustment control;
It is preferable to provide.
The liquefier further includes a liquefaction device for liquefying a part of the boil-off gas compressed by the non-oiling compressor and returning it to the LNG tank from the downstream side of the non-oiling compressor and the upstream side of the first check valve. Is preferred.

It further comprises a first spillback pipe for returning the boil-off gas compressed by the oil supply compressor from the downstream side of the oil supply compressor to the upstream side of the oil supply compressor and further downstream than the first check valve. ,
It is preferable to control the amount of boil-off gas supplied to the propulsion engine by controlling the flow rate of the first spillback pipe.

The LNG carrier is
A second spillback for returning the compressed gas compressed by the upstream oilless compressor from between the outlet of the upstream oilless compressor and the bleed pipe to the upstream side of the upstream oilless compressor Equipped with piping
It is preferable to control the amount of compressed gas supplied to the gas processing system by controlling the flow rate of the second spillback pipe.

The LNG carrier is
The system further comprises a pressure reducing pipe that reduces the pressure of the boil-off gas from the downstream side of the oil supply compressor to a pressure that can be used by the gas processing system and supplies the pressure to the bleed pipe
The bleed pipe preferably includes a second check valve for preventing the backflow of the boil-off gas from the pressure reducing pipe side to the oilless compressor side on the upstream side of the connection portion with the pressure reducing pipe. .

  According to the present invention, the oiling type is provided between the oil-free compressor which compresses the boil-off gas and the oil-feeding compressor which further compresses the boil-off gas compressed by the oil-free compressor and supplies it to the propulsion engine. Since the first check valve is provided to prevent backflow of the compressed gas supplied to the compressor side to the non-oiling type compressor side, there is no boil-off gas mixed with lubricating oil passing through the oil type compressor. It does not return to the refueling compressor side. Therefore, it is possible to prevent the lubricating oil from contaminating the upstream side of the first check valve.

It is a block diagram of the boil off gas utilization system of the LNG carrier concerning the embodiment of the present invention.

Hereinafter, a boil-off gas utilization system for an LNG carrier according to an embodiment of the present invention will be described based on FIG.
The boil-off gas utilization system of the LNG carrier according to the present embodiment is used to use the boil-off gas vaporized in the LNG tank 1 for storing liquefied natural gas in the propulsion engine 2 in the LNG carrier carrying liquefied natural gas. .
In the present embodiment, the multistage compressor 100 that compresses the boil-off gas and transports it from the LNG tank 1 to the propulsion engine 2 includes the non-oiling compressors C1, C2, C3, C4, the oiling compressor C5, 1) A check valve CV1, a liquefier 40 and the like are provided.

The LNG tank 1 stores liquefied natural gas which is a cargo transported by the LNG carrier. Here, natural gas is hydrocarbon gas, which is a fossil fuel produced naturally, or a gas produced from a crude oil refining plant, and includes carbon compounds such as methane, ethane, propane and the like. Liquefied natural gas is obtained by cooling and liquefying natural gas. Although a spherical tank is shown in FIG. 1, the present embodiment is not limited to this, and a membrane tank may be used.
In the present specification, “boil-off gas” is natural gas vaporized in the LNG tank 1, compressed and liquefied natural gas vaporized in the LNG tank 1, and compressed into a supercritical fluid. Including the

  For the oil-free compressors C1 to C4 and the oil-feed compressor C5, for example, a reciprocating compressor may be used, in which a movable portion (plunger or piston) in a compression chamber draws and compresses gas by performing linear alternating motion. it can. The movable parts of the oil-free compressors C1 to C4 and the oil-feeding compressor C5 are interlocked and driven by a crankshaft 19 rotated by the power of a motor M. The boil-off gas is compressed to the fifth power of the compression ratio by being compressed at the same degree of compression ratio in each of the non-oiling compressors C1 to C4 and the oil supply compressor C5. For example, the boil-off gas is compressed to 310 times 3.15 to the power of 5.15 by compressing about 3.15 times in each of the oil-free compressors C1 to C4 and the oil-feeding compressor C5. For example, if the pressure of the boil-off gas at the inlet side of the oilless compressor C1 is 0.1 MPa, the pressure at the outlet side of the oilless compressor C1 is about 0.32 MPa, and the outlet side of the oilless compressor C2 Pressure is about 0.99MPa, pressure on the outlet side of non-lubricated compressor C3 is about 3.13MPa, pressure on the outlet side of nonlubricated compressor C4 is about 9.85MPa, and outlet side of lubricated compressor C5 The pressure of is about 31.0 MPa.

  Buffer tanks (snubbers) (not shown) are provided on the inlet side (suction side) and the outlet side (discharge side) of the non-oiling compressors C1 to C4 and the oiling compressor C5. Further, on the outlet side (discharge side) of the non-oiling compressors C1 to C4 and the oiling compressor C5, a gas cooler (not shown) for cooling boil-off gas whose temperature has risen by being compressed is provided.

  An upper end portion of the LNG tank 1 and an inlet side of the oil-free compressor C1 are connected by a pipe 10. Boil-off gas generated in the LNG tank 1 is sucked by the non-oiling type compressor C 1 and is delivered from the LNG tank 1 through the pipe 10. The pipe 10 passes through the heat exchanger 42 together with a bleed pipe 41 described later, and the boil-off gas passing through the pipe 10 absorbs the heat released from the bleed pipe 41 in the heat exchanger 42. The pipe 10 is provided with a pressure gauge P0. The pressure gauge P0 measures the pressure of the boil-off gas in the pipe 10, and outputs a measurement signal to the pressure control unit PC0.

The outlet side of the oil-free compressor C1 and the inlet side of the oil-free compressor C2 are connected by a pipe 11. The boil-off gas compressed by the oil-free compressor C 1 is sucked by the oil-free compressor C 2 through the pipe 11, further compressed, and discharged to the pipe 12. The pipe 10 and the pipe 11 are connected by a spillback pipe 21. A spill back valve V 1 is provided in the spill back pipe 21, and the boil off gas is returned from the pipe 11 side to the pipe 10 side according to the pressure of the boil off gas in the pipe 11.
The pipe 11 is provided with a pressure gauge P1. The pressure gauge P1 measures the pressure of the boil-off gas in the pipe 11, and outputs a measurement signal to the pressure control unit PC1. The pressure control unit PC1 controls the pressure of the boil-off gas in the pipe 11 by adjusting the opening degree of the spillback valve V1 based on the measurement signal.

The outlet side of the oil-free compressor C2 and the inlet side of the oil-free compressor C3 are connected by a pipe 12. The boil-off gas compressed by the oil-free compressor C 2 is sucked by the oil-free compressor C 3 through the pipe 12, further compressed, and discharged to the pipe 13. The pipe 11 and the pipe 12 are connected by a spill back pipe 22. A spill back valve V2 is provided in the spill back pipe 22, and the boil off gas is returned from the pipe 12 side to the pipe 11 side according to the pressure of the boil off gas in the pipe 12.
The pipe 12 is provided with a pressure gauge P2. The pressure gauge P2 measures the pressure of the boil-off gas in the pipe 12, and outputs a measurement signal to the pressure control unit PC2. The pressure control unit PC2 controls the pressure of the boil-off gas in the pipe 12 by adjusting the opening degree of the spillback valve V2 based on the measurement signal.

The outlet side of the oil-free compressor C3 and the inlet side of the oil-free compressor C4 are connected by a pipe 13. The boil-off gas compressed by the oil-free compressor C 3 is sucked by the oil-free compressor C 4 through the pipe 13, further compressed, and discharged to the pipe 14. The pipe 12 and the pipe 13 are connected by a spillback pipe 23. A spill back valve V3 is provided in the spill back pipe 23. According to the pressure of the boil off gas in the pipe 13, the boil off gas is returned from the pipe 13 side to the pipe 12 side.
The pipe 13 is provided with a pressure gauge P3. The pressure gauge P3 measures the pressure of the boil-off gas in the pipe 13, and outputs a measurement signal to the pressure control unit PC3. The pressure control unit PC3 controls the pressure of the boil-off gas in the pipe 13 by adjusting the opening degree of the spillback valve V3 based on the measurement signal.

The outlet side of the oil-free compressor C4 is connected to one end of the pipe 14, and the other end of the pipe 14 is connected to the upstream side of the check valve CV1. The downstream side of the check valve CV1 is connected to one end of the pipe 15, and the other end of the pipe 15 is connected to the inlet side of the oil type compressor C5. The boil-off gas compressed by the non-oiling compressor C 4 is sucked by the oiling compressor C 5 through the pipes 14 and 15 and the check valve CV 1, further compressed, and discharged to the pipe 16. The pipe 13 and the pipe 14 are connected by a spillback pipe 24. A spill back valve V4 is provided in the spill back pipe 24, and the boil off gas is returned from the pipe 14 side to the pipe 13 side according to the pressure of the boil off gas in the pipe 14.
The pipe 14 is provided with a pressure gauge P4. The pressure gauge P4 measures the pressure of the boil-off gas in the pipe 14, and outputs a measurement signal to the pressure control unit PC4. The pressure control unit PC4 controls the pressure of the boil-off gas in the pipe 14 by adjusting the opening degree of the spillback valve V4 based on the measurement signal.
It should be noted that, instead of providing the spillback pipes 23 and 24 independently in the non-lubrication type compressors C3 and C4, the boil-off gas compressed by the non-lubrication type compressor C4 is not available from the outlet side of the non-lubrication type compressor C4. A spill back pipe may be provided to be returned to the inlet side of the oil type compressor C3.

Further, a liquefying device 40 is connected to the pipe 14. The liquefier 40 includes a bleed pipe 41, a heat exchanger 42, a Joule-Thompson valve (JT valve) 43, a gas-liquid separator 44, and pipes 45, 46.
The bleed pipe 41 is connected to the pipe 14. The bleed pipe 41 passes through the heat exchanger 42 together with the pipe 10, and the boil-off gas passing through the bleed pipe 41 is cooled in the heat exchanger 42 by releasing heat from the bleed pipe 41. The bleed pipe 41 is connected to the gas-liquid separator 44 through the JT valve 43. The boil-off gas passing through the bleed pipe 41 expands at the JT valve 43 while maintaining the pressure difference, and flows into the gas-liquid separator 44.
The JT valve 43 has a porous body through which the boil-off gas passes, and the pressure difference between the boil-off gas at the inlet side and the outlet side of the porous body is maintained. The boil-off gas flows into the gas-liquid separator 44 and is adiabatically expanded to be cooled and a part of the boil-off gas is liquefied. Of the boil-off gas flowing into the gas-liquid separator 44, the gas portion is supplied to the pipe 10 by the pipe 45, and the liquefied portion is returned to the LNG tank 1 by the pipe 46. By returning the liquefied boil-off gas to the LNG tank 1, generation of boil-off gas in the LNG tank 1 can be suppressed.

  In the present embodiment, the boil-off gas compressed by the non-oiling type compressor C4 is extracted from the upstream side of the check valve CV1 upstream of the oiling type compressor C5 by the extraction pipe 41 to the gas-liquid separator 44. In order to flow in and liquefy it and return it to the LNG tank 1, the boil-off gas mixed with the lubricating oil through the oil type compressor C 5 is not returned to the LNG tank 1.

  As shown in FIG. 1, a bleed pipe 31 may be connected to the pipe 12 connecting the outlet side of the non-oiling compressor C2 and the inlet side of the non-oiling compressor C3. In FIG. 1, a check valve CV2 is provided downstream of the bleed pipe 31, a bleed pipe 32 is provided downstream of the check valve CV2, and the bleed pipe 32 is connected to the gas processing system 5. ing. A portion of the boil-off gas compressed by the non-oiling compressor C2 is supplied to the gas processing system 5 through the bleed pipes 31 and 32. For example, the gas processing system 5 is a thermal power generation system that uses excess boil-off gas for power generation. For example, steam generated by the combustion heat of the boil-off gas may be generated, the steam turbine may be rotated by the steam, and the generator may be driven by the steam turbine. Alternatively, the excess boil-off gas may be treated by simply burning it. For example, the heat of combustion may be exhausted into the sea by generating steam with the combustion heat of the boil-off gas, cooling the generated steam with seawater in the condenser, liquefying it, and circulating it.

  When the pressure in the LNG tank 1 rises due to the generation of boil-off gas in the LNG tank 1, it is necessary to suppress the pressure rise in the LNG tank 1 by discharging the boil-off gas from the LNG tank 1. On the other hand, the fuel demand by the propulsion engine 2 is lower than the amount of boil-off gas discharged from the inside of the LNG tank 1 because the fuel demand by the propulsion engine 2 is affected by weather, ocean current, waves and ship maneuvering. There is a case. By supplying boil off gas for the excess demand to the gas processing system 5 through the bleed pipes 31 and 32, pressure increase in the LNG tank 1 can be suppressed.

The bleed pipe 32 is connected to a pipe 35 which leads to the downstream side of the feed compressor C5 as will be described later, and a part of the boil-off gas compressed by the feed compressor C5 is sent to the bleed pipe 32 through the pipe 35. To flow. The check valve CV2 prevents backflow of the boil-off gas from the side of the extraction pipe 32 to the side of the extraction pipe 31 to allow boil-off gas from passing through the oil supply type compressor C5 and mixing with lubricating oil from the side of the extraction pipe 32 It prevents the flow into the bleed pipe 31 side.
The bleed pipe 32 is provided with a pressure gauge P6. The pressure gauge P6 measures the pressure of the boil-off gas in the bleed pipe 32, and outputs a measurement signal to the pressure control unit PC6.

Further, the bleed pipe 32 is provided with a valve V6. The valve V6 is controlled by a valve control unit 37. The valve control unit 37 acquires information on the pressure in the piping 10 from the pressure control unit PC0, and acquires information on the pressure in the bleed piping 32 from the pressure control unit PC6, and the degree of opening of the valve V6 according to the acquired information. The amount of boil off gas supplied to the gas processing system 5 is controlled by adjusting. By adjusting the opening degree of the valve V6 based on the pressure in the pipe 10, it is possible to prevent the pressure in the LNG tank 1 from rising excessively.
In addition, when a part of the boil-off gas compressed by the oil feeding compressor C5 is supplied to the bleed pipe 32 as described later, the pressure in the bleed pipe 32 may be higher than the pressure in the pipe 12. Even in this case, by adjusting the opening degree of the valve V6 based on the pressure in the extraction pipe 32, it is possible to prevent the pressure in the extraction pipe 32 from rising too much.

  When the bleed pipe 31 is connected to the pipe 12, the spillback pipe 23 is the boil-off gas compressed by the non-oiling type compressor C 3 on the inlet side of the non-oiling type compressor C 3 and is the bleed pipe 31 of the pipe 12. It is preferable to return to the downstream side with respect to the connection portion (extraction point) with the If a spillback pipe is provided so as to straddle the bleed point, the amount of boil-off gas flowing toward the bleed pipe 31 fluctuates according to the flow rate of the boil-off gas returned by the spillback pipe, making it difficult to control the flow rate. . Similarly, even when spillback piping is provided to return the boil-off gas compressed by the oil-free compressor C4 from the outlet side of the oil-free compressor C4 to the inlet side of the oil-free compressor C3, oil-free Preferably, the boil-off gas compressed by the compressor C4 is provided downstream of the bleed point.

The outlet side of the feed compressor C5 is connected to one end of the pipe 16, and the other end of the pipe 16 is connected to the upstream side of the check valve CV3. The downstream side of the check valve CV3 is connected to one end of the pipe 17, and the other end of the pipe 17 is connected to the upstream side of the control valve V7. The downstream side of the control valve V7 is connected to one end of the pipe 18, and the other end of the pipe 18 is connected to the propulsion engine 2. The boil-off gas compressed by the feed compressor C5 is supplied to the propulsion engine 2 through the pipes 16, 17 and the check valve CV3.
The piping 15 and the piping 16 are connected by a spillback piping 25. A spill back valve V5 is provided in the spill back pipe 25, and the boil off gas is returned from the pipe 16 side to the pipe 15 side according to the pressure of the boil off gas in the pipe 16.
Further, one end of a pressure reducing pipe 33 is connected to the pipe 16, and the other end of the pressure reducing pipe 33 is connected to one end of the buffer tank 34. The pressure reducing valve 33 is provided in the pressure reducing pipe 33.

  The piping 16 is provided with a pressure gauge P5. The pressure gauge P5 measures the pressure of the boil-off gas in the pipe 16, and outputs a measurement signal to the pressure control unit PC5. The pressure control unit PC5 controls the pressure of the boil-off gas in the pipe 16 by adjusting the opening degree of the spillback valve V5 and a pressure control valve V8 described later based on the measurement signal. That is, by adjusting the opening degree of the spillback valve V5, it is possible to adjust the amount of boil-off gas supplied downstream of the oil type compressor C5. Further, by adjusting the opening degree of the pressure control valve V8, the boil-off gas in the pipe 16 is released to the pressure reducing pipe 33 in response to the rapid fluctuation of the opening degree of the control valve V7 described later, and the impact acting on the pipe 16 Can be relaxed. For example, when the pressure of the boil-off gas in the pipe 16 deviates from the target value, the pressure control unit PC5 turns off the boil-off in the pipe 16 only by the opening degree of the spillback valve V5 if the deviation amount is equal to or less than a predetermined value. By adjusting the pressure of the gas and opening the pressure control valve V8 when the deviation amount exceeds a certain value and the pressure of the boil-off gas in the pipe 16 rises, the pressure of the boil-off gas in the pipe 16 rapidly increases You can prevent that.

  The other end of the buffer tank 34 is connected to one end of the pipe 35, and the other end of the pipe 35 is connected to the bleed pipe 32. When the pressure control valve V8 is opened, part of the boil-off gas compressed by the feed compressor C5 passes through the pressure reducing pipe 33, the pressure control valve V8, the buffer tank 34, the pipe 35, the extraction pipe 32, and the valve V6. It is supplied to the gas treatment system 5. The pressure in the bleed pipe 32 is 1 MPa or less, while the pressure in the pipe 16 is 30 MPa or more. Therefore, the pressure of the boil-off gas is reduced to the pressure in the bleed pipe 32 while passing through the pressure reducing pipe 33, the pressure control valve V8, the buffer tank 34, and the pipe 35. For example, the pressure of the boil-off gas is reduced by using a plurality of valves as the pressure control valve V8, providing an orifice (not shown) in the decompression piping 33 and the piping 35, or the like. In addition, since the boil-off gas is adiabatically expanded by pressure reduction and the temperature is lowered, a heater may be provided to heat the adiabatically expanded boil-off gas. For example, an air heat exchange type heater may be provided on the decompression piping 33 or the piping 35. Further, by providing the buffer tank 34, it is possible to prevent the pressure in the bleed pipe 32 from rising rapidly.

  The propulsion engine 2 burns boil-off gas supplied from the pipe 18 in the combustion chamber to extract power, and causes the main shaft 3 and the propeller 4 to rotate. For the propulsion engine 2, for example, a low-speed diesel engine with a two-stroke cycle can be used. A rotation number meter N is provided on the main shaft 3. The revolution number meter N measures the number of revolutions of the main shaft 3 and outputs a measurement signal to the engine controller ECU. The engine controller ECU adjusts the opening degree of the control valve V7 based on the rotation speed necessary to maintain the propulsive force of the propeller 4 and the measurement signal of the rotation speed meter N. Specifically, the measurement value is higher than the command value so that the rotation speed command value instructed via the console of the LNG carrier matches the measurement value of the rotation speed measured by the rotation speed meter N. If the measured value is lower than the command value, the opening degree of the control valve V7 is lowered.

The pressure of the boil-off gas in the pipe 16 largely fluctuates according to the fluctuation of the opening degree of the control valve V7. For example, when the operation of reducing the rotational speed of the propulsion engine 2 is performed from the console of the LNG carrier, the load (torque) of the propulsion engine 2 is reduced, and the control valve V7 is rapidly closed. Also, when the fuel for the propulsion engine 2 is switched from boil-off gas to another fuel such as heavy oil, the demand for the boil-off gas is zero, and the control valve V7 is rapidly blocked. On the other hand, since the oil feeding compressor C5 is driven by the crankshaft 19 and the crankshaft 19 also drives the oil free compressors C1 to C4, the amount of compression by the oil feeding compressor C5 can not be largely varied.
In the present embodiment, by adjusting the opening degree of the spill back valve V5 and adjusting the opening degree of the pressure control valve V8, fluctuation of the pressure of the boil-off gas in the piping 16 due to fluctuation of the opening degree of the control valve V7. It can reduce the impact of

  The amount of deviation of the pressure of the boil-off gas in the pipe 16 from the target value when the pressure control valve V8 is closed may be smaller than the amount of deviation when the pressure control valve V8 is opened. Thereby, the opening / closing operation of the pressure control valve V8 can be stabilized. For example, the amount of divergence when opening the pressure control valve V8 may be 2.0 MPa, and the amount of divergence when closing the pressure control valve V8 may be 1.5 MPa.

  Further, instead of adjusting the opening degree of the valve V6 based on the pressure in the bleed pipe 32, an accumulator (not shown) may be provided in the bleed pipe 32 to prevent the pressure in the bleed pipe 32 from rising excessively.

  As described above, according to the present embodiment, the check valve CV1 is provided between the oilless compressor C4 and the oiling compressor C5, and the boil-off gas supplied to the oiling compressor C5 is In order to prevent the backflow to the non-oiling compressor C4, the boil-off gas mixed with the lubricating oil after passing through the oil-filled compressor C5 does not return to the non-lubricating compressor C4.

  Therefore, the liquefying device 40 liquefies part of the boil-off gas compressed by the non-oiling compressor C4 and returns it to the LNG tank 1 from the downstream side of the non-oiling compressor C4 and the upstream side of the check valve CV1. Even in the case where it is provided, the boil-off gas mixed with the lubricating oil by passing through the refueling type compressor C5 does not return to the LNG tank 1. Further, among the non-oiling compressors C1 to C4 not using lubricating oil, the downstream side of the non-oiling compressor C4 having the highest discharge pressure and the upstream side of the oiling compressor C5 using lubricating oil In order to return the boil-off gas to the LNG tank 1 from the downstream side of the non-lube type compressor C4 and the upstream side of the check valve CV1, boil-off is prevented while mixing oil is prevented. The gas can be compressed to high pressure and liquefied.

  The spillback pipe 25 is provided to return the boil-off gas compressed by the feed compressor C5 from the downstream side of the feed compressor C5 to the upstream side of the feed compressor C5 and downstream of the check valve CV1. In order to control the flow rate of the back pipe 25, it is possible to control the amount of boil-off gas supplied to the propulsion engine 2 without largely changing the amount of compression by the oil type compressor C5.

  Further, a part of the boil-off gas compressed by the non-oiling compressor C2 is extracted from the upstream of the check valve CV1 by the extraction pipe 31 and the compressed gas supplied from the extraction pipe 31 is used in the gas processing system 5 Thus, the pressure rise in the LNG tank 1 can be suppressed. In addition, the flow rate of the spillback pipe 22 is controlled to return the compressed gas compressed by the non-oiling compressor C2 to the upstream side of the non-oiling compressor C2 from between the outlet of the non-oiling compressor C2 and the bleed pipe 31 Thus, the amount of compressed gas supplied to the gas processing system 5 can be controlled.

Further, the pressure on the downstream side of the check valve CV1 can be controlled by reducing the pressure of the boil-off gas from the downstream side of the feed compressor C5 and controlling the flow rate of the decompression pipe 33 supplied to the gas processing system 5. .
Further, a check valve CV2 is provided on the upstream side of the connection portion of the bleed pipe 32 with the pipe 35 to prevent backflow of the boil-off gas from the pressure reducing pipe 33 to the oilless compressor C2 side. Boil-off gas mixed with lubricating oil after passing through the compressor C5 does not return to the non-oiling compressor C2 side.

  Further, spillback pipes 23 and 24 are provided to the non-oiling compressors C3 and C4, and the boil-off gas compressed by the non-oiling compressors C3 and C4 is extracted from the upstream side of the check valve CV1 through the pipe 12 and the bleed pipe. The pressure of the boil-off gas on the upstream side of the check valve CV1 can be controlled by returning to the downstream side of the connection portion 31 and controlling the flow rate of the spillback piping 23, 24.

Also, instead of separately providing the spillback pipes 21 and 22 in the non-lubrication type compressors C1 and C2, the boil-off gas compressed by the non-lubrication type compressor C2 is not lubricated from the downstream side of the non-lubrication type compressor C2. A spillback pipe may be provided to return to the upstream side of the compressor C1, and pressure control on the upstream side of the check valve CV2 may be performed. Similarly, instead of separately providing the spillback pipes 23 and 24, a spillback pipe is provided for returning from the downstream side of the non-oiling compressor C4 to the upstream side of the non-oiling compressor C3, and Pressure control may be performed.
However, the amount of gas passing through the non-lubrication type compressor C2 and the non-lubrication type compressor C3 differs depending on the flow rate of the piping 31. If the spillback pipe, which is returned to the pipe 12 from the lower upstream of the machine C3, is omitted, the pressure of the pipe 32 tends to fluctuate via the pipe 12 and the check valve CV2, which is disadvantageous.

In the above description, a natural gas carrier mainly composed of carbon compounds such as methane, ethane, propane and the like has been described, but the present invention is not limited thereto, and a carrier of liquefied gas carrying liquefied gas fuel at normal temperature The present invention can be applied to For example, the present invention may be applied to a carrier for liquefied petroleum gas (LPG) which is purified and liquefied by-product gas generated in an oil field, a natural gas field, an oil production facility or the like.
Further, the temperature and pressure in the above description are only an example, and the present invention is not limited to this.

DESCRIPTION OF SYMBOLS 1 LNG tank 2 Propulsion engine 3 Spindle 4 Propeller 5 Gas processing system 10-18, 35, 45, 46 Piping 19 Crankshaft 21-25 Spill back piping 31, 32 and 41 Bleed piping 33 Decompression piping 34 Buffer tank 37 Valve control Part 42 Heat exchanger 43 JT valve 44 Gas-liquid separator 100 Multistage compressor 40 Liquefier C1 to C4 Oilless compressor C5 Feeding type compressor CV1 to CV3 Check valve M Motor N Rotational speed meter P0 to P6 Pressure Total PC0-PC6 Pressure control part V1-V5 Spill back valve V6 valve V7 control valve V8 pressure control valve

Claims (8)

In a boil-off gas utilization system for an LNG carrier carrying liquefied natural gas, the LNG carrier comprises:
LNG tank for storing liquefied natural gas,
A propulsion engine that uses, as a fuel, boil-off gas vaporized in the LNG tank;
A multi-stage compressor for compressing the boil-off gas and transferring it to the propulsion engine;
The multistage compressor is
An upstream oilless compressor for compressing the boil-off gas, and a downstream side downstream of the upstream oilless compressor for further compressing the boil-off gas compressed by the upstream oilless compressor A plurality of oilless compressors , including an oilless compressor;
One or more oiling compressors that further compress the boil-off gas compressed by the non-oiling compressor and supply it to the propulsion engine;
A first non-return provided between the plurality of oilless compressors and the oiling compressor, for preventing the backflow of the compressed gas supplied to the oiling compressor to the oilless compressor Equipped with a valve ,
The LNG carrier further comprises
Bleed piping for extracting compressed gas in which boil-off gas is compressed by the upstream oilless compressor from the upstream of the downstream oilless compressor;
A gas processing system for processing compressed gas supplied from the bleed pipe;
The compressed gas compressed by the downstream oilless compressor from the outlet side of the downstream oilless compressor and the first check valve, the inlet side of the downstream oilless compressor A third spillback pipe for returning the pipe connecting between the upstream oilless compressor and the downstream oilless compressor downstream of the bleed point where the bleed pipe branches off; ,
Boil off gas utilization system of the LNG carrier equipped with. The LNG carrier is provided with a bleed pipe adjustment valve provided in the bleed pipe;
The compressed gas supplied to the gas processing system by adjusting the degree of opening of the bleed pipe adjusting valve based on the pressure of the boil-off gas before being compressed by the non-oiling compressor vaporized from the LNG tank. The boil off gas utilization system of the LNG carrier according to claim 1, wherein the flow rate of the b) is adjusted. In a boil-off gas utilization system for an LNG carrier carrying liquefied natural gas, the LNG carrier comprises:
LNG tank for storing liquefied natural gas,
A propulsion engine that uses, as a fuel, boil-off gas vaporized in the LNG tank;
A multi-stage compressor for compressing the boil-off gas and transferring it to the propulsion engine;
The multistage compressor is
One or more oilless compressors that compress the boil-off gas;
One or more oiling compressors that further compress the boil-off gas compressed by the non-oiling compressor and supply it to the propulsion engine;
A first check valve provided between the oilless compressor and the oiling compressor, for preventing the backflow of the compressed gas supplied to the oiling compressor to the oilless compressor; , And
The LNG carrier further comprises
Boiling piping that bleeds compressed gas in which boil-off gas is compressed by at least one upstream oilless compressor among the oilless compressors from upstream of the first check valve;
A gas processing system for processing compressed gas supplied from the bleed pipe;
A bleed pipe adjustment valve provided in the bleed pipe;
The compressed gas supplied to the gas processing system by adjusting the degree of opening of the bleed pipe adjusting valve based on the pressure of the boil-off gas before being compressed by the non-oiling compressor vaporized from the LNG tank. Boil-off gas utilization system for LNG carriers to adjust the flow rate. The LNG carrier further comprises
A flow control valve for adjusting the flow rate of the boil-off gas supplied to the propulsion engine, between the propulsion engine and the refueling compressor;
First spillback piping for returning the compressed gas compressed by the oil supply compressor from between the outlet of the oil supply compressor and the flow control valve to the upstream side of the oil supply compressor;
A first spillback valve, provided in the first spillback pipe, for adjusting the flow rate of the compressed gas to be returned to the upstream side of the oil type compressor;
Decompression piping which branches from the downstream side of the oil supply compressor, decompresses the boil-off gas to a pressure that can be used by the gas processing system, and supplies the boil off gas to the gas processing system;
A pressure reducing pipe adjusting valve provided in the pressure reducing pipe, for adjusting the flow rate of the boil-off gas flowing from the pressure reducing pipe to the side of the gas processing system;
When the deviation amount of the pressure of the boil off gas from the target pressure before the boil off gas is extracted to the pressure reducing pipe after compression of the boil off gas by the oil supply compressor is equal to or less than a predetermined value, Control is performed to adjust the opening degree of the first spillback valve while maintaining the opening degree, and when the deviation amount exceeds the predetermined value, the opening degrees of the first spillback valve and the pressure reducing pipe adjustment valve A pressure control unit that performs adjustment control;
The boil off gas utilization system of the LNG ship of any one of Claims 1-3 provided with these. The liquefier further includes a liquefaction device for liquefying a part of the boil-off gas compressed by the non-oiling compressor and returning it to the LNG tank from the downstream side of the non-oiling compressor and the upstream side of the first check valve. , LNG ship BOG utilization system according to any one of claims 1-3. It further comprises a first spillback pipe for returning the boil-off gas compressed by the oil supply compressor from the downstream side of the oil supply compressor to the upstream side of the oil supply compressor and further downstream than the first check valve. ,
The boil-off gas utilization system for an LNG carrier according to any one of claims 1 to 3 , wherein the amount of boil-off gas supplied to the propulsion engine is controlled by controlling the flow rate of the first spillback pipe. . The LNG carrier is
A second spillback for returning the compressed gas compressed by the upstream oilless compressor from between the outlet of the upstream oilless compressor and the bleed pipe to the upstream side of the upstream oilless compressor Equipped with piping
The boil-off gas utilization system according to any one of claims 1 to 6 , wherein the supply amount of the compressed gas to the gas processing system is controlled by controlling the flow rate of the second spillback pipe. The LNG carrier is
The pressure reducing pipe is provided from the downstream side of the oil supply type compressor such that the boil-off gas is depressurized to a pressure that can be used by the gas processing system and supplied to the bleed pipe.
The bleed pipe has a second check valve for preventing the backflow of the boil-off gas from the pressure reducing pipe side to the oilless compressor side on the upstream side of the connecting portion with the pressure reducing pipe. The boil off gas utilization system as described in any one of -3 .

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