JP6651689B2 - Fuel gas supply system, ship, and fuel gas supply method - Google Patents

Description

  The present invention relates to a fuel gas supply system that supplies a boil-off gas vaporized from a liquefied gas as a fuel gas to an engine, a ship using the system, and a fuel gas supply method.

  In an LNG carrier, boil-off gas naturally vaporized from liquefied gas stored in a tank is used.

A low pressure fluid, such as boil-off gas, needs to be a high pressure fluid in order to be adapted as engine fuel gas. Therefore, in a fuel gas supply system that supplies boil-off gas as fuel gas for an engine, a compression device, for example, a multi-stage compression device is used to compress fuel gas such as boil-off gas. The compressed fuel gas is sent out to the engine.
On the other hand, the consumption of fuel gas of the engine may change due to load fluctuation or the like. In this case, the boil-off gas is liquefied and returned to the tank in order to effectively collect the excess compressed boil-off gas.

  For example, as a technique for liquefying the compressed boil-off gas and returning it to the tank, after boil-off gas is compressed, a part of the boil-off gas is supplied to the engine, and the remaining boil-off gas is mixed with the low-temperature boil-off gas taken out of the tank and heat. There is known a fuel gas supply system in which a liquefied gas is returned to a tank by liquefaction after heat exchange in an exchanger (Patent Document 1).

JP-A-2005-505941

  In the above fuel gas supply system, when the boil-off gas is liquefied, in addition to the liquefied boil-off gas, there is also a boil-off gas in which the gas is maintained without being liquefied. This boil-off gas is combined with a flow of fresh boil-off gas (hereinafter, also referred to simply as fresh boil-off gas) which has been vaporized and flown from the liquefied gas in the tank to be supplied to the engine after being compressed. At this time, the boil-off gas is not a single kind of component but a mixed gas, and contains a component having a high boiling point and a component having a low boiling point. The component having a low boiling point is likely to remain as a gas in the boil-off gas which is not liquefied and maintains the gas. For this reason, the boil-off gas in which the gas is maintained without being liquefied contains more components having a lower boiling point than the boil-off gas before liquefaction. That is, the composition of the boil-off gas that has been subjected to the liquefaction process but has not been liquefied and has maintained the gas has many components having a lower boiling point than fresh boil-off gas. For this reason, when the boil-off gas, which is not liquefied and maintains the gas, is combined with the fresh boil-off gas, the composition ratio of the boil-off gas supplied to the compression device changes. For example, natural gas may contain several percent of nitrogen, which has a lower boiling point than methane, in addition to methane. In addition, liquefied ethane may contain several percent of methane which has a lower boiling point than ethane. In this case, the boil-off gas circulating between the compression device and the liquefaction device undergoes liquefaction processing repeatedly, so that the content of low-boiling components in the boil-off gas increases with the passage of time. The content of nitrogen contained in the boil-off gas may exceed 10%, and in the case of liquefied ethane, the content of methane contained in the boil-off gas may exceed 50%. Such a change in the composition ratio of the boil-off gas can be achieved by supplying a stable amount (mass) of fuel gas to the engine in a fuel gas supply system including a compression device that determines the amount of boil-off gas to be delivered by controlling the pressure. Becomes difficult.

  When the fuel gas supply system is applied to a ship, the propulsion engine is stopped and the liquefaction device is driven to the maximum to liquefy and collect the boil-off gas when the ship is on standby for cargo handling or waiting for passage through a canal. If this state continues for a long time, a significant change occurs in the composition ratio of the boil-off gas, so that the boil-off gas cannot be effectively used as a fuel gas due to a decrease in calorie as a fuel gas, a change in ignition conditions, a change in combustion, and the like. . Further, in the design of the compression device, it is difficult to cope with a change in flow rate or a change in temperature during the compression of the boil-off gas due to a change in the composition ratio of the boil-off gas. Similarly, a change in the composition ratio of the boil-off gas caused by the liquefaction apparatus at a land base storing natural gas also causes a problem of lowering the liquefaction efficiency. Facilities for removing nitrogen from natural gas (eg, selectively removing nitrogen gas by using a difference in boiling point) are also being studied. However, such equipment is complex and impractical for use on ships. In addition, since the load on the propulsion engine of the ship changes frequently and is not constant, it is difficult to use the above facilities, and the starting of the facilities is not easy, so that the facilities need to be operated and maintained.

  Therefore, the present invention provides a fuel gas supply system and a fuel gas supply system configured such that when a pressurized boil-off gas is supplied to an engine as a fuel gas, the composition ratio of the boil-off gas does not change due to the use of a boil-off gas liquefaction apparatus. It is intended to provide a method and a ship.

One embodiment of the present invention is a fuel gas supply system that supplies a fuel gas to an engine.
The fuel gas supply system includes:
A tank for storing liquefied gas,
A pressurizing mechanism for pressurizing and sending out the boil-off gas vaporized from the liquefied gas, in order to supply the boil-off gas vaporized from the liquefied gas to the engine as a fuel gas,
A liquefier for liquefying a part of the boil-off gas that has been delivered by being pressurized by the pressurizing mechanism and returning the boil-off gas to the tank,
A control device for controlling the amount of boil-off gas flowing to the liquefaction device,
Is provided.
The liquefier includes a recovery pipe for returning a gas-liquid mixed fluid of the liquefied gas liquefied by the liquefier and the boil-off gas that has not been liquefied to the liquid phase of the liquefied gas in the tank.

  It is preferable that a cooling device for cooling the gas-liquid mixed fluid is provided in the recovery pipe.

The fuel gas supply system further includes:
Gas processing control provided in a branch pipe connected to a gas processing device that consumes a part of the boil-off gas pressurized by the pressurizing mechanism, and controlling an amount of boil-off gas flowing through the branch pipe toward the gas processing apparatus. A valve,
A liquefaction control valve for controlling an amount of boil-off gas flowing from the pressurizing mechanism to the liquefaction apparatus.
The control device controls the pressure of the boil-off gas in the tank by controlling the opening degree of one of the gas processing control valve and the liquefaction control valve according to the pressure of the boil-off gas in the tank. Is preferable.

  The control device opens the liquefaction control valve when the sum of the consumption amount of the voice-off gas of the engine and the consumption amount of the boil-off gas of the gas processing device is smaller than the supply amount of the boil-off of the pressurizing mechanism. Is preferably controlled.

  It is preferable that the control device increases the opening speed of the liquefaction control valve continuously or stepwise with the passage of time.

The controller may be configured such that the flow rate of the boil-off gas is 20% of the optimal recovery gas amount, which is the maximum boil-off gas flow rate at which the liquefaction apparatus can liquefy the boil-off gas most from the start of opening of the liquefaction control valve. as the time to reach the more than one minute, the controls the opening of the liquefaction control valve, it is preferable.

  The control device, when opening the liquefaction control valve, from the gas processing control state that controls the opening degree of the gas processing control valve according to the pressure of the boil-off gas in the tank, to the pressure of the boil-off gas in the tank It is preferable to control the liquefaction control valve and the gas processing control valve so as to shift to a liquefaction control state in which the degree of opening of the liquefaction control valve is controlled accordingly.

The control of the opening degree of the gas processing control valve by the control device is performed through a gas processing selector connected to the gas processing control valve,
The control of the opening degree of the liquefaction control valve by the control device is performed through a liquefaction selector connected to the liquefaction control valve,
A gas processing feedback control signal that instructs an opening degree of the gas processing control valve so that the pressure of the boil-off gas in the tank becomes a set gas processing pressure set value,
Irrespective of the pressure of the boil-off gas in the tank, a gas processing sequence control signal indicating the opening degree of the gas processing control valve so that the pressure of the boil-off gas in the tank becomes a predetermined pressure, and the gas To the processing selector,
A liquefaction feedback control signal that instructs an opening degree of the liquefaction control valve so that the pressure of the boil-off gas in the tank becomes a set liquefaction pressure set value,
A liquefaction sequence control signal indicating the opening degree of the liquefaction control valve so that the pressure of the boil-off gas in the tank becomes a predetermined pressure, irrespective of the pressure of the boil-off gas in the tank; To the vessel,
The gas processing selector, among the gas processing feedback control signal and the gas processing sequence control signal, selects the larger control signal of the indication value of the opening and sends the selected control signal to the gas processing control valve,
It is preferable that the liquefaction selector selects a control signal having the smaller instruction value of the opening degree from the liquefaction feedback control signal and the liquefaction sequence control signal, and sends the selected control signal to the liquefaction control valve.

  When the liquefaction control valve is closed, the gas processing pressure set value is lower than the liquefaction pressure set value, and when the liquefaction control valve is open, the gas processing pressure set value is the liquefaction pressure. It is preferable to adjust the gas processing pressure set value and the liquefaction pressure set value so as to be larger than the set values.

  When the liquefaction control valve is closed, the control device controls the opening degree of the gas processing control valve so that the pressure of the boil-off gas in the tank becomes the gas processing pressure set value. Preferably, when the valve is open, the opening of the liquefaction control valve is controlled so that the pressure of the boil-off gas in the tank becomes the liquefaction pressure set value.

Another aspect of the present invention provides
The fuel gas supply system;
And a propulsion engine driven by using fuel pressurized by the pressurizing mechanism.

Still another embodiment of the present invention relates to a fuel gas supply method for supplying a fuel gas to an engine. The fuel gas supply method is as follows:
A step of pressurizing and sending out the boil-off gas vaporized from the liquefied gas by a pressurizing mechanism to supply the vaporized boil-off gas from a tank storing the liquefied gas to the engine as a fuel gas,
A gas-liquid mixed fluid containing a non-liquefied boil-off gas, which is generated by liquefying a part of the boil-off gas delivered under pressure by a liquefaction device, is returned to the liquid phase of the liquefied gas in the tank. And

  It is preferable that the fuel gas supply method further includes a step of cooling the gas-liquid mixed fluid before returning the mixed gas to the tank.

The fuel gas supply method further includes flowing a part of the pressurized boil-off gas toward a gas processing device that consumes the fuel as fuel,
One of the amount of the boil-off gas flowing toward the gas processing device and the amount of the gas-liquid mixed fluid returned to the liquid phase of the liquefied gas in the tank depends on the pressure of the boil-off gas in the tank. It is preferable to control the pressure of the boil-off gas in the tank by controlling.

  When the sum of the consumption amount of the voice-off gas of the engine and the consumption amount of the boil-off gas of the gas processing device is smaller than the supply amount of the boil-off of the pressurizing mechanism, the gas-liquid mixed fluid is liquefied gas in the tank. It is preferable to perform a step of returning to the liquid phase.

  When liquefaction is started by flowing the boil-off gas through the liquefaction apparatus, it is preferable to increase the amount of the boil-off gas flowing through the liquefaction apparatus continuously or stepwise over time.

  When liquefaction is started by flowing the boil-off gas into the liquefaction apparatus, the flow rate of the boil-off gas is 20% of the optimal recovery gas amount, which is the maximum boil-off gas flow rate at which the boil-off gas can be liquefied most by the liquefaction apparatus. It is preferable to control the flow rate of the boil-off gas flowing through the liquefaction apparatus so that the time until the flow rate reaches 1 minute or more.

  When liquefaction is started by flowing the boil-off gas into the liquefaction apparatus, the gas is supplied in accordance with the pressure of the boil-off gas in the tank so that the pressure of the boil-off gas in the tank becomes a target gas processing pressure set value. From the gas processing control state of controlling the amount of boil-off gas flowing to the processing device, the pressure of the boil-off gas in the tank is adjusted to a target liquefaction pressure set value so that the pressure of the boil-off gas in the tank is controlled according to the pressure of the boil-off gas in the tank. It is preferable to control the flow of the boil-off gas so as to shift to a liquefaction control state in which the amount of the boil-off gas flowing to the liquefaction device is controlled.

  According to the fuel gas supply system, the fuel gas supply method, and the marine vessel of the above aspect, when the pressurized boil-off gas is supplied to the engine as the fuel gas, the composition ratio of the boil-off gas does not change, and the pressure is increased to a predetermined pressure. The generated voice off gas can be stably supplied to the engine.

1 is a diagram illustrating an example of a configuration of a fuel gas supply system according to a first embodiment. It is a figure which shows the principal part containing the junction pipe of the conventional liquefaction apparatus. It is a figure which shows an example of the compression characteristic of a boil-off gas which changes with the change of the composition ratio of a boil-off gas. (A), (b) is a figure which shows the example of the time change of the pressure and the opening degree of a control valve in the fuel gas supply system of this embodiment.

  Hereinafter, a fuel gas supply system, a ship, and a fuel gas supply method of the present invention will be described in detail.

  FIG. 1 is a diagram illustrating an example of a configuration of a fuel gas supply system 10 that supplies a boil-off gas of a liquefied gas as a fuel gas to a propulsion engine of a ship according to the present embodiment. Liquefied natural gas is used as the liquefied gas of the fuel gas supply system 10, but is not limited to liquefied natural gas, and a liquefied gas of pure methane or a liquefied gas such as ethane can be used. The boil-off gas includes, in addition to the gas vaporized by natural heat input in the tank, a gas that is intentionally heated to forcibly vaporize LNG. In the present embodiment, a description will be given using a gas vaporized by natural heat input in the tank. When using a gas that has been forcibly vaporized, a forced vaporizer for vaporizing the boil-off gas from the liquefied gas is provided.

The fuel gas supply system 10 is used to supply boil-off gas vaporized in a tank 20 for storing liquefied natural gas to a propulsion engine 40 as fuel gas in an LNG carrier that transports liquefied natural gas. In the present embodiment, one propulsion engine 40 is provided, but a plurality of propulsion engines may be connected to branch pipes branched from the main pipe.
In this specification, the direction in which boil-off gas is supplied from the tank 20 to the propulsion engine 40 is referred to as a downstream direction, the opposite direction is referred to as an upstream direction, and the downstream side from a reference position is referred to as a downstream side. Is referred to as the upstream side from the position.

  In the fuel gas supply system of the present embodiment, as described below, the liquefied gas liquefied from the boil-off gas by the liquefier and the liquefied gas are not liquefied so that the composition ratio of the boil-off gas in the pressurizing mechanism and the liquefier does not change. The mixed fluid of the boil-off gas, which still maintains the gas, is always returned to the liquid phase of the liquefied gas in the tank 20. Therefore, since the composition ratio of the boil-off gas does not change due to the use of the boil-off gas liquefaction apparatus, the voice-off gas pressurized to a predetermined pressure can be stably supplied to the engine.

The fuel gas supply system 10 of the present embodiment mainly includes a tank 20, a pressurizing mechanism 30, a liquefaction device 50, and a control device 60. Specifically, the fuel gas supply system 10 includes a pipe such as a branch pipe, and a control valve and an adjustment valve provided on the pipe. A pressurizing mechanism 30 is provided on a main pipe 31 through which boil-off gas extends from the tank 20 to the propulsion engine 40.
The pressurizing mechanism 30 is a device that pressurizes and sends out the boil-off gas vaporized from the liquefied gas in order to supply a part of the boil-off gas to the propulsion engine 40 as a fuel gas.
The liquefaction device 50 is a device for liquefying a part of the boil-off gas sent out after being pressurized by the pressurizing mechanism 30 and collecting it in the tank 20.
The control device 60 is a device that controls the flow of the boil-off gas of the fuel gas supply system 10, and is a device that adjusts at least the opening of the control valve and the control valve provided in the pressurizing mechanism 30, the liquefaction device 50, and the like. is there.

(Pressure mechanism)
The pressurizing mechanism 30 includes gas compressors (pressurizing devices) 32a to 32e, bypass pipes 33a, 33c, 33e, adjusting valves 34a, 34c, 34e, suction snubbers 35a to 35e, and discharge snubbers 36a to 36e. It mainly includes heat exchangers 37a to 37e.
Each of the suction snubbers 35a to 35e is provided on the upstream side of each of the gas compressors 32a to 32e, temporarily stores the boil-off gas, and is configured so that the boil-off gas is smoothly suctioned to each of the gas compressors 32a to 32e. This is a container with space. Each of the discharge snubbers 36a to 36e is a container provided with a space that is provided downstream of each of the gas compressors 32a to 32e and configured to temporarily store the boil-off gas and smoothly deliver the boil-off gas. Each of the heat exchangers 37a to 37e is provided on the downstream side of each of the discharge snubbers 36a to 36e, and cools the boil-off gas which has become hot when pressurized.

The gas compressors 32a to 32e are multi-stage pressurizing devices connected in series for pressurizing (compressing) and sending out the boil-off gas. The gas compressors 32a to 32e are portions that suck the boil-off gas in the suction snubber and pressurize the gas to a predetermined pressure. The gas compressors 32a to 32e use, for example, a reciprocating compressor that sucks boil-off gas from the suction snubbers 35a to 35e by moving a movable portion (plunger or piston) in the gas compressors 32a to 32e in a linear reciprocating motion and then pressurizes the boil-off gas. be able to. Among the gas compressors 32a to 32e, the gas compressors 32a to 32d use oilless compressors, and the gas compressor 32e that pressurizes boil-off gas to a high pressure uses an oil supply compressor. The movable parts of the gas compressors 32a to 32e are driven in conjunction with each other via a rotating shaft (not shown) that is rotated by the power of a driving source (not shown) whose driving is controlled by the control device 60. In the gas compressors 32a to 32e, the boil-off gas is compressed stepwise at approximately the same compression rate, so that the boil-off gas is compressed to the fifth power of the compression rate. For example, by compressing the three to four times in each of the gas compressors 32 a to 32 e, BOG is compressed in ³ 5-4 ⁵ times. For example, if the pressure of the boil-off gas on the suction side of the gas compressor 32a is 0.1 MPa, the pressure on the discharge (delivery) side of the gas compressor 32a is about 0.33 MPa, and the pressure on the discharge side of the gas compressor 32b is about 1. The pressure on the discharge side of the gas compressor 32c is about 3.64 MPa, and the pressure on the discharge side of the gas compressor 32d is about 12.06 MPa. Then, the pressure on the discharge side of the gas compressor 32e is increased to a set target pressure, for example, 39.9 Mpa.

The bypass pipe 33a connects the suction snubber 35a and the output end of the heat exchanger 37b, bypassing the gas compressors 32a and 32b, that is, the pipe section through which the boil-off gas before pressurization by the gas compressor 32a flows, and the gas compressor. A pipe through which boil-off gas flows, which connects pipes through which boil-off gas flows after pressurization by 32b.
In addition, the bypass pipe 33c connects the suction snubber 35c and the output end of the heat exchanger 37d, bypassing the gas compressors 32c and 32d, that is, the bypass pipe 33c and the pipe portion through which the boil-off gas before pressurization by the gas compressor 32c flows. This pipe connects the pipes through which the boil-off gas flows after being pressurized by the gas compressor 32d, and through which the boil-off gas flows.
The bypass pipe 33e bypasses the gas compressor 32e and connects the suction snubber 35e to the output end of the heat exchanger 37e. That is, the bypass pipe 33e is connected to a pipe portion through which boil-off gas flows before pressurization by the gas compressor 32e and the gas compressor 32e. A pipe through which boil-off gas flows, which connects pipes through which boil-off gas flows after pressurization.

  The bypass pipes 33a, 33c, 33e are provided with adjusting valves 34a, 34c, 34e for adjusting the opening. Each of the bypass pipes 33a, 33c, 33e is provided with a pressure gauge 38a, 38c, 38e for measuring the pressure of the boil-off gas pressurized by the gas compressor 32b, 32d, 32e. The pressure gauges 38a, 38c, 38e need not be provided on the bypass pipes 33a, 33c, 33e as long as the pressure of the boil-off gas at the branch point where the bypass pipes 33a, 33c, 33e branch off from the main pipe 31 can be measured. Absent. Each of the adjusting valves 34a, 34c, 34e is provided so as to be adjusted based on the pressure information measured by the pressure gauges 38a, 38c, 38e. In FIG. 1, the pressure gauges 38a, 38c, 38e and the adjustment valves 34a, 34e are used to indicate that the opening degrees of the adjustment valves 34a, 34c, 34e are controlled based on the pressures measured by the pressure gauges 38a, 38c, 38e. A dotted line connecting 34c and 34e is drawn. Specifically, information on the measured pressure measured by the pressure gauges 38a, 38c, 38e is sent to the control device 60. The control device 60 generates a control signal for feedback control for controlling the amount of boil-off gas flowing through the bypass pipes 33a, 33c, 33e based on the difference between the sent measured pressure and the set pressure, and generates this control signal. It is sent to the adjustment valves 34a, 34c, 33e.

For example, when 1500 kg of boil-off gas is supplied per hour from the upstream side and the gas compressors 32a and 32b or the gas compressors 32c and 32d or the gas compressor 32e pressurizes and sends out 2000 kg of boil-off gas per hour to the downstream side, A boil-off gas of 500 kg per hour is caused to flow (backflow) through the bypass pipe 33a, the bypass pipe 33c or the bypass pipe 33e, and returned to the upstream side of the gas compressors 32a and 32b or the gas compressors 32c and 32d or the gas compressor 32e. In this way, the opening degrees of the adjustment valves 34a, 34c, 34e provided in the bypass pipes 33a, 33c, 33e are controlled so that 500 kg of boil-off gas flows per hour. Thereby, the pressure on the downstream side of the gas compressor 32a, 32b, the gas compressor 32c, 32d, or the gas compressor 32e can be adjusted to a predetermined pressure. By adjusting the pressure to a predetermined value, the boil-off gas flowing from the pressurizing mechanism 30 to the propulsion engine 40 can be adjusted to the fuel gas pressure and the fuel supply amount required by the propulsion engine 40.
In the present embodiment, the bypass pipe 33a is provided so as to bypass the gas compressors 32a and 32b at the same time, and the bypass pipe 33c is provided so as to bypass the gas compressors 32c and 32d at the same time. May be provided.

In the pressurizing mechanism 30 of the present embodiment, a check valve 31a is provided between the fourth-stage gas compressor 32d and the fifth-stage gas compressor 32e. Oil contained in the boil-off gas delivered from the gas compressor 32e, which is a refueling compressor, is supplied to the gas compressor 32d, which is an oilless compressor, and the gas compressors 32b, 32c, which are upstream of the gas compressor, and which flows out of the refueling compressor. A check valve 31a is provided to prevent impurities such as flowing into the gas compressor 32d and contaminating devices such as the gas compressors 32b and 32c upstream thereof.
Further, a check valve may be provided between the first-stage gas compressor 32a and the second-stage gas compressor 32b counted from the upstream side.
Further, a check valve 31b is provided downstream of the bypass pipe 33e so that the boil-off gas once supplied to the engine 40 does not flow backward toward the upstream side.

A branch pipe 39 branches from a branch point where the bypass pipe 33a branches from the main pipe 31 and a junction point where the bypass pipe 33c merges with the main pipe 31, and is connected to the gas processing device 70. The gas processing device 70 is a device that processes boil-off gas, and may be connected to steam utilization equipment or power generation equipment, or may be a device that simply incinerates boil-off gas. As described later, it is preferable that the boil-off gas can be treated even if the composition ratio of the boil-off gas, for example, the ratio of a component having a low boiling point in the boil-off gas changes. For example, when the gas processing device 70 is a four-cycle internal combustion engine used for a generator, the configuration is such that the air-fuel ratio and the ignition timing can be adjusted to respond to changes in the composition ratio of the boil-off gas. Is preferred. Further, it is preferable that the gas processing device 70 has a capacity capable of consuming the entire amount of the boil-off gas generated from the tank 20.
The branch pipe 39 extending to the gas processing device 70 is provided with a check valve 31 c so that the boil-off gas flowing toward the gas processing device 70 does not flow back toward the pressurizing mechanism 30. Further, a gas processing control valve 71 is provided in the branch pipe 39 so as to adjust the amount of boil-off gas to be processed by the gas processing device 70. The opening degree of the gas processing control valve 71 is controlled based on the pressure measured by a pressure gauge 57b provided in the main pipe 31 described later. Since the installation place of the pressure gauge 57b is a part of the main pipe 31 on the upstream side of the pressurizing mechanism 30 connected to the space occupied by the boil-off gas in the tank 20, the measured pressure of the pressure gauge 57a is It is also the pressure of the boil-off gas. The pressure measured by the pressure gauge 57a is sent to the control device 60. The pressure control signal 60 generates a control signal for controlling the opening of the gas processing control valve 71a based on the pressure measured by the pressure gauge 57a (the pressure of the boil-off gas in the tank 20). It is sent to the control valve 71a.

(Propulsion engine)
The propulsion engine 40 is provided on the boat used in the present embodiment. As the propulsion engine 40, for example, a dual fuel engine that can use oil such as heavy oil as fuel while using boil-off gas of liquefied gas as fuel gas is used.
The propulsion engine 40 burns the supplied boil-off gas as fuel gas in a combustion chamber to extract power, and rotates a main shaft (not shown) connected to the propulsion engine 40 and a propeller (not shown) and a propeller of the ship. As the propulsion engine 40, for example, a two-stroke cycle low-speed diesel engine can be used.

The propulsion engine 40 is connected to an engine control unit (hereinafter, referred to as ECU) 62, and its driving is controlled by the ECU 62. The ECU 62 supplies fuel gas to the propulsion engine 40 such that the main shaft rotation speed measured by the tachometer 42 provided to measure the rotation of the main shaft connecting the propulsion engine 40 and the propeller becomes the target rotation speed. The driving of the propulsion engine 40 is controlled by controlling the opening of the pressure control valve 44 provided in the supply line. That is, the ECU 62 determines the load on the propulsion engine 40 such that the main shaft rotation speed of the main shaft connecting the propulsion engine 40 and the propeller for propulsion becomes the target rotation speed, and controls the flow rate of the fuel gas based on the load. It is. The ECU 62 determines the load on the propulsion engine 40 so that the main shaft rotation speed, which changes due to changes in natural conditions such as weather, wind of the sea, and wave height, is maintained at the target rotation speed. The load on the propulsion engine 40 can also be determined according to the operation command value of the propeller speed provided by the instruction. In FIG. 1, a dotted line connecting the rotation system 42 and the pressure control valve 44 is simply drawn to represent the above-described control.
The ECU 62 is configured to set a target pressure on the delivery side of the gas compressor 32e located at the most downstream, based on the determined load, and to send the target pressure to the control device 60. The target pressure is a fuel supply pressure required by the propulsion engine 40 to the fuel gas supply system 30. The pressurization control device 62 controls the amount of boil-off gas delivered by the pressurization mechanism 30 using the target pressure.

(Liquefaction equipment)
The liquefaction apparatus 50 is connected to the pressurizing mechanism 30 through a branch pipe 51 that branches from a branch point of the bypass pipe 33c from the main pipe 31 and between the check valve 31a.
The liquefaction device 50 is a device that returns the boil-off gas that has become unnecessary due to a change in the load of the propulsion engine 40 to the tank 20 as liquefied gas. Part of the boil-off gas is not liquefied and maintains a gas. In the present embodiment, the boil-off gas is pumped together with the liquefied gas into a liquefied gas in the tank 20 in a gas-liquid mixed fluid state. The liquefaction apparatus 50 includes a heat exchanger 53 for cooling the boil-off gas before liquefying the boil-off gas, an expansion valve 54 for expanding and liquefying the cooled boil-off gas, and a gas-liquid mixed fluid created by the expansion valve 54 in the tank 20. It mainly comprises a recovery pipe 56 for returning the liquefied gas inside to the liquid phase, and a cooler 58.
The expansion valve 54 expands and cools the cooled boil-off gas. The expansion valve 54 may be a valve that changes during an isenthalpic process such as a JT (Joule Thomson) valve, but is preferably a valve that changes during an isentropic process such as an expander.
The cooler 58 cools the gas-liquid mixed fluid flowing through the recovery pipe 58 in order to reduce the amount of heat flowing into the tank 20. As described above, since the cooling device 58 that cools the gas-liquid mixed fluid generated by the expansion valve 54 is provided in the recovery pipe 56, the gas-liquid mixed fluid is not added to the liquefied gas in the tank 20 without adding a large amount of heat. It is preferable because it can be recovered.

  The branch pipe 51 extending from the pressurizing mechanism 30 is provided with a liquefaction control valve 55 for controlling the flow rate of the boil-off gas flowing in the liquefaction apparatus 50. In the present embodiment, the liquefaction control valve 55 is provided between the heat exchanger 53 and the expansion valve 54. On the other hand, the main pipe 31 extending from the tank 20 to the pressurizing mechanism 30 has a pressure of the boil-off gas in the tank 20, that is, the boil-off gas before being pressurized by the pressurizing mechanism 30, in other words, the boil-off gas in the tank 20. A pressure gauge 57a for measuring pressure is provided.

  The liquefaction control valve 55 is provided with a selector (liquefaction selector) 57b that sends a control signal to the liquefaction control valve 55. The selector 57b sends a control signal for the opening degree of the liquefaction control valve 55 generated based on the pressure measured by the pressure gauge 57a (hereinafter, this control signal is referred to as a liquefaction feedback control signal) and the control device 60 to the contact 57c. Out of the control signals of the opening degree of the liquefaction control valve 55 generated based on the sequence for the liquefaction processing of the boil-off gas (hereinafter, this control signal is referred to as a liquefaction sequence control signal). This is a low-order selector for selecting a signal. The information on the pressure measured by the pressure gauge 57a is sent to the control device 60, and the control device 60 generates a liquefaction feedback control signal for controlling the opening of the liquefaction control valve 55 based on the pressure measured by the pressure gauge 57a. This liquefaction feedback control signal is sent to the selector 57b. In FIG. 1, the pressure gauge 57a and the selector 57b are connected by a dotted line for easy understanding. The control device 60 generates an opening control signal based on the difference between the pressure measured by the pressure gauge 57a and the liquefaction pressure set value so that the pressure of the pressure gauge 57a becomes a preset liquefaction pressure set value. Is configured. Specifically, when the pressure measured by the pressure gauge 57a is higher than the liquefaction pressure set value, the control device 60 increases the opening of the liquefaction control valve 55 so that the pressure measured by the pressure gauge 57a is larger than the liquefaction pressure set value. When it is low, the liquefaction control valve 55 is configured to generate a liquefaction feedback control signal that reduces the opening degree. Such a liquefaction pressure set value is set in the control device 60. The opening degree of the generated liquefaction feedback control signal is compared with the opening degree of the liquefaction sequence control signal sent from the control device 60 through the contact 57c by the selector 57b. The control signal is selected and sent to the liquefaction control valve 55. In other words, the control device 60 generates a liquefaction feedback control signal based on the pressure measured by the pressure gauge 57a, and also controls the liquefaction control valve 55 according to the sequence for the liquefaction processing of the boil-off gas regardless of the magnitude of the measured pressure. Is configured to generate a liquefaction sequence control signal for controlling the degree of opening through the contact 57c.

Further, the control device 60 controls the opening degree of the gas processing control valve 71a that controls the flow rate of the boil-off gas to the gas processing device 70. The gas processing control valve 71a is connected to a selector (a gas processing selector) 71c. The selector 71c controls the opening degree of the gas processing control valve 71a based on the pressure measured by the pressure gauge 57a (hereinafter, this control signal is referred to as a gas processing feedback control signal). Among the control signals for the opening degree of the gas processing control valve 71a generated based on the sequence for the gas processing of the boil-off gas (hereinafter, this control signal is referred to as a gas processing sequence control signal). This is a high-order selector that selects the larger control signal.
As described above, since information on the pressure measured by the pressure gauge 57a is sent to the control device 60, the control device 60 opens the gas processing control valve 71a based on the pressure measured by the pressure gauge 57a. A gas processing feedback control signal for controlling the degree is generated, and this gas processing feedback control signal is sent to the selector 71c. In FIG. 1, the pressure gauge 57a and the selector 71c are connected by a dotted line for easy understanding. The control device 60 generates an opening control signal based on the difference between the pressure measured by the pressure gauge 57a and the gas processing pressure set value so that the pressure of the pressure gauge 57a becomes a preset gas processing pressure set value. It is configured to be. Specifically, when the pressure measured by the pressure gauge 57a is higher than the gas processing pressure set value, the control device 60 increases the opening of the gas processing control valve 71a, and the pressure measured by the pressure gauge 57a becomes the gas processing pressure setting. If the value is lower than the value, the gas processing control valve 55 is configured to generate a gas processing feedback control signal for decreasing the opening degree. Such a gas processing pressure set value is set in the control device 60. The opening degree of the generated gas processing feedback control signal is compared with the opening degree of the gas processing sequence control signal sent from the control device 60 through the contact 57c by the selector 71c. (Large) control signal is selected and sent to the gas processing control valve 71a. That is, the control device 60 generates a gas processing feedback control signal based on the pressure measured by the pressure gauge 57a, and performs gas processing control according to the sequence for gas processing of boil-off gas regardless of the magnitude of the measured pressure. It is configured to generate a gas processing sequence control signal for controlling the opening degree of the valve 71a through the contact 71b.

  In the liquefaction apparatus 50, the temperature of the gas-liquid mixed fluid generated by the expansion of the boil-off gas by the expansion valve 54 is higher than the temperature of the liquefied gas in the tank 20. When the gas-liquid mixed fluid flows into the liquefied gas, heat temporarily flows into the liquefied gas in the tank 20. Therefore, in order to prevent the vaporization of the liquefied gas in the tank 20 from increasing and the pressure in the tank 20 from temporarily increasing, the speed at which the opening of the liquefaction control valve 55 increases is initially small, and The control device 60 performs control so that the value increases continuously or intermittently with the passage of time. More specifically, the liquefaction control valve is configured to cool the boil-off gas by the heat exchanger 53 and expand the boil-off gas by the expansion valve 54 to reduce the flow rate of the maximum boil-off gas, which is the maximum flow rate of the boil-off gas, which is smaller than the optimal recovery gas amount. Initially, the opening speed of the liquefaction control valve 55 is small so that the liquefaction control valve 55 flows through the liquefaction device 50 when the 55 is opened. Thereafter, the control device 60 increases the opening speed of the liquefaction control valve 55 continuously or intermittently with time so that the boil-off gas flowing in the liquefaction device 50 approaches the optimal recovery gas amount. Thus, the opening of the liquefaction control valve 55 is controlled. Such a control signal is input from the control device 60 to the contact 57c. In this case, when the liquefaction control valve 55 is opened, the control device 60 controls the opening degree of the liquefaction control valve 55 so that the time required to reach the boil-off gas flow rate of 20% of the optimum recovered gas amount is 1 minute or more. Is preferred.

  The liquefied gas in the mixed fluid returned to the liquefied gas in the tank 20 is stored as a liquefied gas in the tank 20. On the other hand, the boil-off gas in the mixed fluid is returned to the liquid phase of the liquefied gas, so that a large amount of the boil-off gas is dissolved in the liquefied gas and floats as a boil-off gas in the gas phase of the tank 20. Therefore, a large amount of boil-off gas is dissolved in the liquefied gas in the tank 20 and is recovered as the liquefied gas.

  FIG. 2 is a diagram showing a configuration of a pipe or the like downstream of the expansion valve 54 of the conventional liquefaction apparatus 50. As shown in FIG. 2, a gas-liquid separator 59 is provided to separate the gas-liquid mixed fluid generated by the expansion valve 54 into a liquefied gas and a boil-off gas, and the liquefied gas is collected in the tank 20 by a collection pipe 156. On the other hand, when the boil-off gas is combined with the flow of the boil-off gas vaporized in the tank 20 flowing through the main pipe 31 through the merge pipe 57, the composition ratio of the boil-off gas changes as described above, Boil-off gas control becomes difficult.

  While the liquefied gas liquefied from the boil-off gas among the boil-off gases is recovered in the tank 20, the unliquefied boil-off gas circulates in the pressurizing mechanism 30 and the liquefaction device 50. The composition ratio of the boil-off gas pressurized by the pressure mechanism 30 changes with time. That is, the boil-off gas that merges with the fresh boil-off gas before pressurization flowing through the main pipe 31 drawn from the tank 20 through the merge pipe 57 is the unliquefied boil-off gas separated from the liquefied gas in the liquefier 50, The ratio of the low boiling point component of the boil-off gas is higher than that of the boil-off gas in the tank 20. For this reason, the composition ratio of the boil-off gas to be pressurized changes with time. That is, the composition ratio of the component having a lower boiling point than the main component of the liquefied gas in the boil-off gas increases. When the liquefied gas in the tank 20 is natural gas, the main component is methane, ethane or the like, but the natural gas contains a small amount of nitrogen having a boiling point lower than that of methane or ethane. On the other hand, the ratio of the nitrogen component in the boil-off gas that has passed through the liquefaction apparatus 50 increases. For example, even when 1% of nitrogen is mixed in the liquefied natural gas, the nitrogen ratio of the boil-off gas that has passed through the liquefaction device 50 is determined by controlling the control state in which the boil-off gas circulates in the pressurizing mechanism 30 and the liquefaction device 50 for a long time. If maintained, it increases to more than 10%. As the ratio of nitrogen increases, the amount of liquefied gas recovered to the tank 20 through the recovery pipe 156 decreases, and the pressure of the boil-off gas by the gas compressors 32a to 32e in the pressurizing mechanism 30 increases as described later. As a result, the amount of boil-off gas flowing through the bypass pipes 33a, 33c gradually increases due to the adjustment of the degree of opening of the adjustment valves 34a, 34c. .

FIG. 3 is a diagram showing an example of the relationship between the pressure and the volume of the boil-off gas received in the compression processing by the gas compressor. Among the boil-off gases of the liquefied gas, the boil-off gas containing only a main component that does not contain a component having a low boiling point rises from the pressure P1 to the pressure P2 according to the path A when compressed from the volume V1 to the volume V2. . On the other hand, the boil-off gas containing a component having a low boiling point rises from the pressure P1 to the pressure P3 (P3> P2) according to the path B even when subjected to the compression treatment with the same volume change. For this reason, the energy consumed by the gas compressor in the same compression processing using the boil-off gas containing a component having a low boiling point is larger than that of the boil-off gas containing no component having a low boiling point.
As described above, by increasing the pressure of the boil-off gas pressurized by the same compression processing, control of the delivery amount (mass) of the boil-off gas by the pressurizing mechanism 30 (by-pass pipes 33a, 33c, 33e by the adjustment valves 34a, 34c, 34e). Pressure-based control of the amount of boil-off gas flowing through).

  Therefore, in the present embodiment, the gas-liquid mixed fluid generated by the liquefaction device 50 is returned to the liquid phase in the tank 20. Therefore, the composition ratio of the boil-off gas does not change, and the voice-off gas pressurized to a predetermined pressure can be stably supplied to the engine.

  By controlling the opening of the gas processing control valve 71a before the liquefaction control valve 55 is opened in the liquefaction apparatus 50, the liquefaction control valve 55 is opened from the gas processing control state in which the pressure of the boil-off gas in the tank 20 is controlled. The behavior of shifting to another control state will be described.

When the load on the propulsion engine 40 is large and the consumption of the boil-off gas is large, the sum of the consumption of the boil-off gas of the propulsion engine 40 and the consumption of the boil-off gas of the gas processing device 70 is the amount of the boil-off gas generated in the tank 20. Beyond. In this case, the propulsion engine 40 uses oil such as heavy oil as a supplementary fuel. In this control state, the control device 60 preferably sets the gas processing pressure set value lower than the liquefied gas pressure set value, and the gas processing pressure set value is, for example, 50 kPa, and the liquefied pressure set value is , For example, 100 kPa. The control device 60 is configured to send a liquefaction sequence control signal having an opening of 0 (completely closed) to the contact 57c and a gas processing control signal having an opening of 0 to the contact 71b.
Therefore, the liquefaction control valve 55 is completely closed by selecting the liquefaction sequence control signal of the opening degree 0 sent to the contact 57c by the selector 57b, and the gas treatment control valve 71a is opened by the selector 71c to the contact 71b. The gas processing sequence control signal of 0 is not selected, and the gas processing feedback control signal generated based on the pressure of the pressure gauge 57a is selected. Therefore, the opening of the gas processing control valve 71a is controlled based on the pressure of the pressure gauge 57a, and is controlled so that the pressure of the pressure gauge 57a (the pressure of the boil-off gas in the tank 20) becomes the gas processing pressure set value. ing. Therefore, in this control state, the pressure of the boil-off gas in the tank 20 is controlled within a predetermined range by operating and controlling the opening of the gas processing control valve 71a in accordance with the pressure of the boil-off gas in the tank 20. It is a gas processing control state.

  Thereafter, when the speed of the boat is reduced to some extent and the load on the propulsion engine 40 is reduced, the sum of the consumption of the boil-off gas of the propulsion engine 40 and the consumption of the boil-off gas of the gas processing device 70 is determined by the pressurizing mechanism 30. The supply amount of the boil-off gas (in the present embodiment, substantially corresponds to the amount of boil-off gas generated). In this case, the consumption of supplementary fuel using oil such as heavy oil is reduced to zero.

  When the consumption of the boil-off gas of the propulsion engine 40 further decreases, the sum of the consumption of the boil-off gas of the propulsion engine 40 and the consumption of the boil-off gas of the gas processing device 70 becomes smaller than the supply of the boil-off gas by the pressurizing mechanism 30. That is, a part of the voice off gas becomes surplus. Along with this, the pressure of the pressure gauge 57a (the pressure of the boil-off gas in the tank 20) increases. However, since the opening of the gas processing control valve 71a is controlled to open in accordance with this increase, the gas processing apparatus The consumption of boil-off gas by 70 increases. That is, the surplus boil-off gas is consumed by the gas processing device 70.

  When the opening of the gas processing control valve 71a exceeds the set threshold value, the control device 60 generates a liquefaction sequence control signal that causes the liquefaction control valve 55 to open so that the boil-off gas flows into the liquefaction device 50. That is, when the sum of the consumption amount of the voice-off gas of the propulsion engine 40 and the consumption amount of the boil-off gas of the gas processing device 70 is smaller than the supply amount of the boil-off of the pressurizing mechanism 30, the liquefaction control valve 55 is opened. I do. In the control state immediately before the liquefaction control valve 55 is opened, the gas processing pressure set value is lower than the liquefaction pressure set value, for example, 50 kPa. The liquefaction pressure set value is, for example, 100 kPa. A gas processing sequence control signal in which the opening degree of the gas processing control valve 71a is 0 is sent to the contact 71b, and the opening degree of the gas processing control valve 71a is determined based on the gas generated based on the pressure measured by the pressure gauge 57a. It is controlled according to the processing feedback control signal. On the other hand, a liquefaction sequence control signal in which the degree of opening of the liquefaction control valve 55 is 0 is sent to the contact 57c, and the degree of opening of the liquefaction control valve 55 is 0 in accordance with the liquefaction sequence control signal. Therefore, in this control state, the liquefaction pressure set value does not function for the liquefaction control valve 55.

FIGS. 4 (a) and 4 (b) show the time changes of the pressure measured by the pressure gauge 57a, the liquefaction pressure set value, and the gas processing pressure set value, and the opening of the liquefaction control valve 55 in the liquefaction feedback control signal and the liquefaction sequence control signal. It is a figure showing an example of a time change of a degree. Time T1 represents the time at which the liquefaction control valve 55 opens.
As shown in FIG. 4A, the measured pressure of the pressure gauge 57a (the pressure of the boil-off gas in the tank 20) substantially matches the set value of the gas processing pressure.
From such a control state, the control device 60 performs the following operations 1 and 2 at time T1. Further, the control device 60 performs the following operation 3. By these operations, the control signal for controlling the opening of the gas processing control valve 71a is changed from the gas processing feedback control signal based on the pressure measured by the pressure gauge 57a to the gas processing sequence control signal sent from the control device 60 to the contact 71b. Then, the control signal for controlling the opening degree of the liquefaction control valve 55 is changed from the liquefaction sequence control signal sent from the control device 60 to the contact 57c to the liquefaction feedback control signal based on the pressure measured by the pressure gauge 57a.

Operation 1:
The controller 60 changes the gas processing pressure set value to be larger and the liquefaction pressure set value to be smaller, and sets the gas processing pressure set value to be larger than the liquefaction pressure set value. In this case, the changed gas processing pressure set value is, for example, 80 kPa, and the changed liquefaction pressure set value is, for example, 50 kPa. Further, the control device 60 sends a gas processing sequence control signal to the contact 71b so that the desired amount of boil-off gas required for consumption by the gas processing device 70 flows, and sets the opening of the liquefied gas control valve 55 to 0. The liquefaction sequence control signal is maintained and sent to the contact 57c.
In the state of the operation 1, the opening degree of the gas processing control valve 71a is changed according to the gas processing feedback control signal generated based on the difference between the pressure measured by the pressure gauge 57a and the gas processing pressure set value having the increased value. Since the difference is increased, the opening degree of the gas processing control valve 71a is reduced. For this reason, as shown in FIG. 4A, the pressure measured by the pressure gauge 57a increases so as to approach the gas processing pressure set value. As described later, at time T1, the liquefaction control valve 55 starts to open, but since the opening speed is small, a sufficient gas-liquid mixed fluid is not collected in the tank 20, so that the measured pressure of the pressure gauge 57a is reduced. It rises so as to approach the gas processing pressure set value.

Operation 2:
At time T1, controller 60 sends a liquefaction sequence control signal that slowly opens liquefaction control valve 55 and has a non-zero opening degree as a control signal to be sent to contact point 57c.
With the liquefaction sequence control signal, the liquefaction control valve 55 starts opening slowly through the selector 57b. In this case, a liquefaction sequence control signal is generated such that the speed of opening of the liquefaction control valve 55 is initially small and gradually increases. Specifically, when the liquefaction control valve 55 is initially opened, cooling of the boil-off gas by the heat exchanger 53 and expansion of the boil-off gas by the expansion valve 54 cause the maximum boil-off gas to liquefy most. The opening speed of the liquefaction control valve 55 is initially small so that a small flow rate flows in the liquefaction device 50. Thereafter, the speed of the opening of the liquefaction control valve 55 is gradually increased so that the boil-off gas flowing in the liquefaction device 50 approaches the optimal recovery gas amount. Such a control signal is input from the control device 60 to the contact 57c. In this case, when the liquefaction control valve 55 starts to open from the opening degree 0, the opening speed of the liquefaction control valve 55 is controlled so that it takes one minute or more to reach the boil-off gas flow rate of 20% of the optimal recovered gas amount. Preferably.

In this state, initially, when the gas-liquid mixed fluid starts to be collected in the tank 20, the pressure measured by the pressure gauge 57a increases until the amount of collection increases, but when the gas processing pressure approaches the gas processing pressure set value (for example, 80 kPa). The gas processing feedback control signal based on the pressure measured by the pressure gauge 57a is sent to the gas processing control valve 71a through the selector 71c, and the pressure increase of the pressure gauge 57a is suppressed.
Further, the degree of opening of the liquefaction control valve 55 is increased by the liquefaction sequence control signal sent to the contact 57c, and the pressure of the pressure gauge 57a starts to decrease as shown in FIG. The opening of the liquefaction sequence control signal gradually increases as shown in FIG. 4B, and crosses the opening of the liquefaction feedback control signal. Degree. Thus, the selector 57b selects the liquefaction feedback control signal based on the pressure measured by the pressure gauge 57a, and the opening of the liquefaction control valve 55 is controlled by the liquefaction feedback control signal. That is, the control signal for controlling the degree of opening of the liquefaction control valve 55 is changed from the liquefaction sequence control signal sent to the contact 57c to the liquefaction feedback control signal based on the pressure measured by the pressure gauge 57a.

  On the other hand, since the pressure measured by the pressure gauge 57a is lower than the gas processing pressure set value, the opening degree of the gas processing feedback control signal becomes smaller. Thus, the opening of the gas processing feedback control signal is lower than the opening of the gas processing sequence control signal sent from the control device 60 to the contact 71b. As a result, the selector 71c selects the gas processing sequence control signal, and the control signal for controlling the opening of the gas processing control valve 71a is sent to the contact 71b from the gas processing feedback control signal based on the measured pressure of the pressure gauge 57a. Is changed to a gas processing sequence control signal. Therefore, the opening of the gas processing control valve 71a can be adjusted by adjusting the opening of the gas processing sequence control signal.

Operation 3:
When the opening degree of the gas processing feedback control signal becomes smaller than the opening degree of the gas processing sequence control signal, a rewriting process for rewriting the value of the gas processing sequence control signal to the gas processing feedback control signal of the control device 60 is performed. On the other hand, when the opening degree of the gas processing sequence control signal is smaller than the opening degree of the gas processing feedback control signal, the rewriting process is not performed. The gas processing feedback control signal is a control signal based on PID control (Proportional-Integral-Differential Controller), and is generated based on the integrated value of the residual difference between the past gas processing feedback control signal and the measured pressure. Therefore, when the load of the propulsion engine 40 fluctuates due to disturbance and the consumption amount of the boil-off gas fluctuates and the pressure measured by the pressure gauge 57a fluctuates rapidly, the PID control of the opening degree by the gas processing control valve 55 is stabilized. In order to be able to do it.

  The liquefaction of the boil-off gas in the liquefaction apparatus 50 and the stoppage of the recovery of the gas-liquid mixed fluid in the tank 20 are performed by setting the liquefaction sequence control signal to the signal of the opening degree 0, and setting the liquefaction pressure set value to the boil-off gas liquefaction and the gas-liquid What is necessary is just to return to the state before the collection of the mixed fluid in the tank 20, and to set the gas processing sequence control signal to the signal of the opening degree 0.

  As described above, the liquefier 50 of the present embodiment is provided with the recovery pipe 56, and the gas-liquid mixed fluid of the liquefied gas liquefied by the liquefier 50 and the boil-off gas not liquefied through the recovery pipe 56 is supplied to the liquefied gas in the tank 20. In the liquid phase. Therefore, as shown in FIG. 2, when the boil-off gas is combined with the flow of the boil-off gas flowing through the main pipe 31 through the merge pipe 57, the boil-off gas is caused by a change in the composition ratio of the boil-off gas caused by the merge. It is possible to avoid difficulties in controlling the pressurization of the boil-off gas in the pressurizing mechanism 30. Therefore, the composition ratio of the boil-off gas does not change, and the voice-off gas pressurized to a predetermined pressure can be stably supplied to the propulsion engine 40.

  The control device 60 controls the opening degree of one of the gas processing control valve 71a and the liquefaction control valve 55 according to the pressure of the boil-off gas in the tank 20, thereby controlling the pressure (pressure) of the boil-off gas in the tank 20. Controlling the pressure of the boil-off gas in the tank 20 within a predetermined range, and preventing the tank 20 from being damaged due to an increase in the pressure of the boil-off gas. ,preferable.

  When the sum of the consumption amount of the voice off gas of the propulsion engine 40 and the consumption amount of the boil off gas of the gas processing device 70 is smaller than the supply amount of the boil off gas of the pressurizing mechanism 30, the control device 60 activates the liquefaction control valve 55. It is preferable to control the boil-off gas to open so as to prevent the boil-off gas in the tank 20 from rising beyond a predetermined range as the boil-off gas in the pressurizing mechanism 30 rises.

The control device 60 decreases the speed of the opening of the liquefaction control valve 55 by increasing the speed of the opening of the liquefaction control valve 55 continuously or stepwise with the passage of time. Then, since the gas-liquid mixed fluid having a higher temperature than the liquefied gas flows into the tank 20, it is possible to suppress a large amount of heat from entering the liquefied gas in the tank 20. When a large amount of heat enters the liquefied gas, the amount of boil-off gas generated sharply increases and the pressure of the boil-off gas in the tank 20 deviates from a predetermined range, causing a safety problem.
The control device 60 determines that the flow rate of the boil-off gas is 20% of the optimal recovery gas amount, which is the maximum boil-off gas flow rate at which the liquefaction device 50 can liquefy the boil-off gas most from the start of opening the liquefaction control valve 55. By controlling the opening degree of the liquefaction control valve 55 and controlling the flow rate of the boil-off gas flowing to the liquefaction device 50 so that the time until the liquefied gas reaches the liquefier 50 is 1 minute or more. This is preferable from the viewpoint of preventing heat from entering.

  When opening the liquefaction control valve 55, the controller 60 changes the gas processing control state in which the opening degree of the gas processing control valve 71a is controlled in accordance with the pressure of the boil-off gas in the tank 20, from the gas processing control state to the pressure of the boil-off gas in the tank 20. Since the liquefaction control valve 55 and the gas processing control valve 71a are controlled so as to shift to the liquefaction control state in which the opening degree of the liquefaction control valve 55 is controlled accordingly, the pressure of the boil-off gas in the tank 20 in the two control states is controlled. Can be suppressed within a predetermined range.

  Further, as described above, the selector 71c outputs the control signal having the larger indication value of the opening degree between the gas processing feedback control signal generated by the control device 60 and the gas processing sequence control signal generated by the control device 60. The selected value is sent to the gas processing control valve 7a. As described above, the selector 57b outputs the indication value of the opening degree between the liquefaction feedback control signal generated by the control device 60 and the liquefaction sequence control signal generated by the control device 60. Since the smaller control signal is selected and sent to the liquefaction control valve 55, the transition from the gas processing control state to the liquefaction control state can be easily performed. The selectors 57b and 71c are provided separately from the control device 60, but may be incorporated in the control device 60. Further, the control device 60 may be configured by a controller that generates a liquefaction sequence control signal and a gas processing sequence control signal, and a controller that generates a liquefaction feedback control signal and a gas processing feedback control signal. In addition, the controller that generates the liquefaction feedback control signal and the gas processing feedback control signal may be configured as separate units of a controller that generates the liquefaction feedback control signal and a controller that generates the gas processing feedback control signal.

  As described above, when the liquefaction control valve 55 is closed, the controller 60 sets the gas processing pressure set value lower than the liquefaction pressure set value, and when the liquefaction control valve is opened, the gas processing pressure set value becomes the liquefaction pressure. The gas processing pressure set value and the liquefaction pressure set value are adjusted so as to be larger than the set values. Thereby, it is possible to easily shift from the gas processing control state in which the pressure of the boil-off gas is controlled to the gas processing pressure set value to the liquefaction control state in which the pressure of the boil-off gas in the tank 20 is controlled to the liquefaction pressure set value.

  Further, as described above, when the liquefaction control valve 55 is closed, the control device 60 adjusts the opening of the gas processing control valve 71a so that the pressure of the boil-off gas in the tank 20 becomes the gas processing pressure set value. When the liquefaction control valve 55 is open, the opening degree of the liquefaction control valve 55 is controlled such that the pressure of the boil-off gas in the tank 20 becomes the liquefaction pressure set value. Accordingly, in any control state, the pressure of the boil-off gas in the tank 20 can be controlled to a desired pressure.

  Such a fuel gas control system 10 performs a fuel gas supply method including the following steps.

(1) A step of pressurizing and sending out the boil-off gas vaporized from the liquefied gas by the pressurizing mechanism 30 to supply the vaporized boil-off gas from the tank 20 storing the liquefied gas to the propulsion engine 40 as a fuel gas.
(2) The gas-liquid mixed fluid containing the unliquefied boil-off gas, which is generated by liquefying a part of the boil-off gas sent out under pressure by the liquefaction device 50, is used as the liquid phase of the liquefied gas in the tank 20. Step back in.

  In this method, it is preferable that the method further includes a step of cooling the gas-liquid mixed fluid with the cooling device 58 before returning to the tank 20.

The fuel gas supply method further includes:
And (3) flowing a part of the pressurized boil-off gas toward the gas processing device 70 that consumes the boil-off gas as fuel.
In this case, one of the amount of the boil-off gas flowing toward the gas processing device 70 and the amount of the gas-liquid mixed fluid returned to the liquid phase of the liquefied gas in the tank 20 is determined by the pressure of the boil-off gas in the tank 20 ( It is preferable to control the pressure of the boil-off gas in the tank 20 by controlling according to the pressure measured by the pressure gauge 57a).

  In the fuel gas supply method, when the sum of the consumption amount of the voice-off gas of the engine 40 and the consumption amount of the boil-off gas of the gas processing device 70 is smaller than the supply amount of the boil-off of the pressurizing mechanism 30, the gas-liquid mixed fluid is stored in the tank. Preferably, a step of returning the liquefied gas in the liquid phase 20 to the liquid phase is performed.

  Further, when liquefaction is started by flowing the boil-off gas through the liquefier 50, it is preferable to increase the amount of the boil-off gas flowing through the liquefier 50 continuously or stepwise over time.

  When liquefaction is started by flowing the boil-off gas into the liquefaction apparatus 50, the flow rate of the boil-off gas is 20% of the optimal recovery gas amount which is the maximum boil-off gas flow rate at which the liquefaction apparatus 50 can liquefy the boil-off gas most. It is preferable to control the flow rate of the boil-off gas flowing through the liquefier 50 so that the time required to reach the flow rate is 1 minute or more.

  When liquefaction is started by flowing the boil-off gas through the liquefaction apparatus 50, the gas processing is performed in accordance with the pressure of the boil-off gas in the tank 20 so that the pressure of the boil-off gas in the tank 20 becomes a target gas processing pressure set value. From the gas processing control state in which the amount of boil-off gas flowing to the device 70 is controlled, the liquefaction is performed in accordance with the pressure of the boil-off gas in the tank 20 so that the pressure of the boil-off gas in the tank 20 becomes a target liquefaction pressure set value. It is preferable to control the flow of the boil-off gas so as to shift to a liquefaction control state in which the amount of the boil-off gas flowing to the device 50 is controlled.

  As described above, the fuel gas supply system, the fuel gas supply method, and the ship according to the present invention have been described in detail. However, the present invention is not limited to the above embodiment, and various improvements and modifications may be made without departing from the gist of the present invention. Of course, you can do it.

Reference Signs List 10 fuel gas supply system 20 tank 30 pressurizing mechanism 31 main pipes 32a to 32e gas compressors 33a, 33c, 33e bypass pipes 34a, 34c, 34e, 55a, 57a adjustment valves 35a to 35e suction snubbers 36a to 36e discharge snubbers 37a to 37e Heat exchangers 38a, 38b, 38c, 38d Check valves 38a, 38c, 38e, 65a, 65b Pressure gauge 39 Branch pipe 40 Propulsion engine 42 Tachometer 44 Flow control valve 50 Liquefier 51 Branch pipe 53 Heat exchanger 54 Expansion valve 55 Liquefaction control valve 56 Recovery pipe 57a Pressure gauge 57b, 71c Selector 57c, 71b Contact point 58 Cooler 60 Controller 62 Engine control unit 70 Gas processing unit 71a Gas processing control valve 156 Recovery pipe

Claims (18)

A fuel gas supply system that supplies fuel gas to an engine,
A tank for storing liquefied gas,
A pressurizing mechanism for pressurizing and sending out the boil-off gas vaporized from the liquefied gas, in order to supply the boil-off gas vaporized from the liquefied gas to the engine as a fuel gas,
A liquefier for liquefying a part of the boil-off gas that has been delivered by being pressurized by the pressurizing mechanism and returning the boil-off gas to the tank,
A control device for controlling the amount of boil-off gas flowing to the liquefaction device,
With
The fuel, wherein the liquefier includes a recovery pipe for returning a gas-liquid mixed fluid of a liquefied gas liquefied by the liquefier and a boil-off gas not liquefied into a liquid phase of the liquefied gas in the tank. Gas supply system.   The fuel gas supply system according to claim 1, wherein a cooling device that cools the gas-liquid mixed fluid is provided in the recovery pipe. The fuel gas supply system further includes:
Gas processing control provided in a branch pipe connected to a gas processing device that consumes a part of the boil-off gas pressurized by the pressurizing mechanism, and controlling an amount of boil-off gas flowing through the branch pipe toward the gas processing apparatus. A valve,
A liquefaction control valve for controlling the amount of boil-off gas flowing from the pressurizing mechanism to the liquefaction apparatus,
The control device controls the pressure of the boil-off gas in the tank by controlling the opening degree of one of the gas processing control valve and the liquefaction control valve according to the pressure of the boil-off gas in the tank. The fuel gas supply system according to claim 1, wherein:   The control device opens the liquefaction control valve when the sum of the consumption amount of the voice off gas of the engine and the consumption amount of the boil off gas of the gas processing device is smaller than the supply amount of the boil off gas of the pressurizing mechanism. The fuel gas supply system according to claim 3, wherein the control is performed as follows.   5. The fuel gas supply system according to claim 3, wherein the control device increases the speed of the degree of opening of the liquefaction control valve continuously or stepwise over time. 6. The controller may be configured such that the flow rate of the boil-off gas is 20% of the optimal recovery gas amount, which is the maximum boil-off gas flow rate at which the liquefaction apparatus can liquefy the boil-off gas most from the start of opening of the liquefaction control valve. The fuel gas supply system according to claim 5, wherein the opening degree of the liquefaction control valve is controlled so that the time until the temperature reaches 1 minute or more.   The control device, when opening the liquefaction control valve, from the gas processing control state that controls the opening degree of the gas processing control valve according to the pressure of the boil-off gas in the tank, to the pressure of the boil-off gas in the tank The fuel gas according to any one of claims 3 to 6, wherein the liquefaction control valve and the gas processing control valve are controlled so as to shift to a liquefaction control state in which the degree of opening of the liquefaction control valve is controlled accordingly. Feeding system. The control of the opening degree of the gas processing control valve by the control device is performed through a gas processing selector connected to the gas processing control valve,
The control of the opening degree of the liquefaction control valve by the control device is performed through a liquefaction selector connected to the liquefaction control valve,
A gas processing feedback control signal that instructs an opening degree of the gas processing control valve so that the pressure of the boil-off gas in the tank becomes a set gas processing pressure set value,
Irrespective of the pressure of the boil-off gas in the tank, a gas processing sequence control signal indicating the opening degree of the gas processing control valve so that the pressure of the boil-off gas in the tank becomes a predetermined pressure, and the gas To the processing selector,
A liquefaction feedback control signal that instructs an opening degree of the liquefaction control valve so that the pressure of the boil-off gas in the tank becomes a set liquefaction pressure set value,
A liquefaction sequence control signal indicating the opening degree of the liquefaction control valve so that the pressure of the boil-off gas in the tank becomes a predetermined pressure, irrespective of the pressure of the boil-off gas in the tank; To the vessel,
The gas processing selector, of the gas processing feedback control signal and the gas processing sequence control signal, selects the larger control signal of the indication value of the opening degree and sends the selected control signal to the gas processing control valve,
8. The liquefaction control device according to claim 3, wherein the liquefaction selector selects a control signal having a smaller indication value of the opening degree from the liquefaction feedback control signal and the liquefaction sequence control signal and sends the control signal to the liquefaction control valve. 9. The fuel gas supply system according to claim 1.   When the liquefaction control valve is closed, the gas processing pressure set value is lower than the liquefaction pressure set value, and when the liquefaction control valve is open, the gas processing pressure set value is the liquefaction pressure. The fuel gas supply system according to claim 8, wherein the gas processing pressure set value and the liquefaction pressure set value are adjusted so as to be larger than a set value.   When the liquefaction control valve is closed, the control device controls the opening degree of the gas processing control valve so that the pressure of the boil-off gas in the tank becomes the gas processing pressure set value. The fuel gas supply system according to claim 9, wherein when the valve is open, the opening of the liquefaction control valve is controlled such that the pressure of the boil-off gas in the tank becomes the liquefaction pressure set value. A fuel gas supply system according to any one of claims 1 to 10,
And a propulsion engine driven by using fuel pressurized by the pressurizing mechanism. A fuel gas supply method for supplying fuel gas to an engine,
A step of pressurizing and sending out the boil-off gas vaporized from the liquefied gas by a pressurizing mechanism to supply the vaporized boil-off gas from a tank storing the liquefied gas to the engine as a fuel gas,
A gas-liquid mixed fluid containing a non-liquefied boil-off gas, which is generated by liquefying a part of the boil-off gas delivered under pressure by a liquefaction device, is returned to the liquid phase of the liquefied gas in the tank. And a fuel gas supply method.   13. The fuel gas supply method according to claim 12, further comprising a step of cooling the gas-liquid mixed fluid before returning the mixed gas to the tank. The fuel gas supply method further includes flowing a part of the pressurized boil-off gas toward a gas processing device that consumes the fuel as fuel,
One of the amount of the boil-off gas flowing toward the gas processing device and the amount of the gas-liquid mixed fluid returned to the liquid phase of the liquefied gas in the tank depends on the pressure of the boil-off gas in the tank. 14. The fuel gas supply method according to claim 12, wherein the control controls the pressure of the boil-off gas in the tank.   When the sum of the consumption amount of the voice-off gas of the engine and the consumption amount of the boil-off gas of the gas processing device is smaller than the supply amount of the boil-off of the pressurizing mechanism, the gas-liquid mixed fluid is liquefied gas in the tank. The method for supplying a fuel gas according to claim 14, wherein the step of returning to the liquid phase is performed.   The fuel gas supply according to claim 14 or 15, wherein when liquefaction is started by flowing the boil-off gas through the liquefaction apparatus, the amount of the boil-off gas flowing through the liquefaction apparatus is increased continuously or stepwise over time. Method.   When liquefaction is started by flowing the boil-off gas into the liquefaction apparatus, the flow rate of the boil-off gas is 20% of the optimal recovery gas amount, which is the maximum boil-off gas flow rate at which the boil-off gas can be liquefied most by the liquefaction apparatus. 17. The fuel gas supply method according to claim 16, wherein a flow rate of the boil-off gas flowing through the liquefaction device is controlled such that a time until the flow rate reaches 1 minute or more. When liquefaction is started by flowing the boil-off gas into the liquefaction apparatus, the gas is supplied in accordance with the pressure of the boil-off gas in the tank so that the pressure of the boil-off gas in the tank becomes a target gas processing pressure set value. From the gas processing control state of controlling the amount of boil-off gas flowing to the processing device, the pressure of the boil-off gas in the tank is adjusted to a target liquefaction pressure set value so that the pressure of the boil-off gas in the tank depends on the pressure of the boil-off gas in the tank. The fuel gas supply method according to any one of claims 14 to 17, wherein the flow of the boil-off gas is controlled so as to shift to a liquefaction control state in which the amount of the boil-off gas supplied to the liquefaction device is controlled.

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