JP6651688B2 - 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, since the boil-off gas circulating between the compression device and the liquefaction treatment device repeatedly undergoes the liquefaction treatment, the content of the low-boiling component in the boil-off gas increases with the passage of time. In this case, 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 relates to a case in which a boil-off gas is supplied to the engine as a fuel gas under a pressurized boil-off gas including a use condition in which a composition ratio of the boil-off gas changes by use of a boil-off gas liquefaction apparatus. However, an object of the present invention is to provide a fuel gas supply system, a fuel gas supply method, and a ship that can stably supply a voice-off gas pressurized to a predetermined pressure to an engine.

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 that pressurizes and sends out the boil-off gas vaporized from the liquefied gas as fuel in order to supply the boil-off gas vaporized from the liquefied gas as a fuel gas to an engine,
An apparatus for liquefying a part of the boil-off gas pressurized and sent out by the pressurizing mechanism, wherein the collection controls the amount of the liquefied gas to be collected in the tank out of the liquefied gas generated by liquefaction of the boil-off gas. A liquefaction device comprising a control valve;
A gas that is 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 as a fuel, and controls an amount of the boil-off gas flowing through the branch pipe toward the gas processing device. A process control valve;
A control device for adjusting the opening of the recovery control valve and the gas processing control valve.
The control device, by controlling the degree of opening of the gas processing control valve, the total amount of consumption of boil-off gas by the engine and the gas processing device and the amount of liquefied boil-off gas collected in the tank, The control state 1 in which the supply amount of the boil-off gas sent out by the pressurizing mechanism is made to match, and the supply of the boil-off gas to the engine is stopped, and the opening degree of the gas processing control valve is changed to the gas processing in the control state 1. The boil-off flow is switched between a control state 2 in which the opening degree of the recovery control valve is larger than the opening degree of the control valve and an opening degree of the recovery control valve is smaller than the opening degree of the recovery control valve in the control state 1. Is configured.

The liquefaction device is a confluence control valve that controls the amount of boil-off gas that is not liquefied by the liquefaction device and that is vaporized from the liquefied gas and condensed with the boil-off gas before being pressurized by the pressurizing mechanism. With
It is preferable that the control device makes the opening of the merge control valve smaller in the control state 2 than in the control state 1.

The control state 1 includes a static state 1 in which the merge control valve is closed, and a static state 2 in which the merge control valve is open,
It is preferable that the control device performs control for switching from the stationary state 2 to the control state 2.

  Furthermore, the fuel gas supply system includes a determination device that determines whether or not the composition ratio of the boil-off gas pressurized by the pressurizing mechanism has changed. In this case, it is preferable to switch from the control state 1 to the control state 2 when the determination device determines a change in the boil-off gas generation ratio.

  The pressurizing mechanism is a pressurizing device that pressurizes the boil-off gas, and a pipe through which boil-off gas flows before and after pressurization by the pressurizing device, a bypass pipe connected around the pressurizing device, An adjusting valve for controlling an amount of the boil-off gas flowing through the bypass pipe such that a pressure of the boil-off gas after pressurization by the pressurizing device falls within a predetermined range. In this case, it is preferable that the determination device determines the change in the composition ratio of the boil-off gas based on the information on the opening degree of the adjustment valve in the control state 1.

  In this case, it is preferable that the determination device determines that the composition ratio of the boil-off gas has changed when the opening degree changes with the elapsed time and falls outside a predetermined range.

  It is also preferable that the determination device determines a change in the composition ratio of the boil-off gas based on energy consumed per unit time by the pressurizing mechanism in the control state 1 to pressurize the boil-off gas.

  In this case, it is preferable that the determination device determines that the composition ratio of the boil-off gas has changed when the consumed energy changes with the elapsed time and falls outside a predetermined range.

  Further, the liquefaction apparatus includes a pipe connected to the branch pipe connected to the gas processing apparatus so that the boil-off gas that has maintained a gas without being liquefied among the boil-off gas flows toward the gas processing apparatus. Is preferred.

  In this case, a heat exchanger is provided that raises the temperature of the boil-off gas flowing through the pipe connected to the branch pipe of the liquefier by heat exchange with the boil-off gas before liquefaction flowing from the pressurizing mechanism to the liquefier. Is preferable.

Another aspect of the present invention is 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:
Pressurizing and delivering the boil-off gas vaporized from the liquefied gas as fuel to supply the boil-off gas vaporized from the tank storing the liquefied gas to the engine as fuel gas;
Processing a part of the pressurized boil-off gas as a fuel in a gas processing device;
Liquefying a part of the pressurized boil-off gas and collecting it in the tank.
By controlling the amount of boil-off gas flowing to the gas treatment device, the total amount of boil-off gas consumption by the engine and the gas treatment device and the amount of liquefied boil-off gas collected in the tank, The control state 1 in which the supply amount of the gas is made to match, and the supply of the boil-off gas to the engine is stopped, and the consumption amount of the boil-off gas by the gas processing apparatus is reduced by the consumption amount of the boil-off gas by the gas processing apparatus in the control state 1. And the flow of boil-off gas is switched between control states 2 in which the amount of boil-off gas recovered to the tank is smaller than the amount of boil-off gas recovered to the tank in the control state 1.

  In the control state 2, it is preferable that the amount of the boil-off gas, which is maintained without being liquefied among the boil-off gases, being combined with the flow of the boil-off gas flowing out of the tank is smaller than that in the control state 1.

  The control state 1 is a stationary state 1 in which the boil-off gas of the boil-off gas, the gas of which is maintained without being liquefied, is not combined with the flow of the boil-off gas before pressurization vaporized from the liquefied gas, and A stationary state 2 in which the boil-off gas that has maintained the gas without being liquefied is combined with the flow of the boil-off gas before pressurization vaporized from the liquefied gas. In this case, the control state 2 is preferably switched from the static state 2.

  It is preferable to switch from the control state 1 to the control state 2 when the composition ratio of the boil-off gas changes.

  A pressurizing mechanism for pressurizing the boil-off gas is connected between a pressurizing device for pressurizing the boil-off gas and a pipe through which the boil-off gas flows before and after pressurization by the pressurizing device, bypassing the pressurizing device. And a regulating valve for controlling the amount of boil-off gas flowing through the bypass pipe such that the pressure of the boil-off gas after pressurization by the pressurizing device falls within a predetermined range. In this case, it is preferable that the change in the composition ratio of the boil-off gas be determined in the control state 1 based on information on the opening degree of the adjustment valve.

  In this case, it is preferable to determine that the composition ratio of the boil-off gas has changed when the opening degree changes with the lapse of time and falls outside a predetermined range.

  It is also preferable that a change in the composition ratio of the boil-off gas is determined based on energy consumed per unit time consumed by the pressurizing device in the control state 1 to pressurize the boil-off gas.

  In this case, it is preferable to determine that the composition ratio of the boil-off gas has changed when the consumed energy changes with the lapse of time and falls outside a predetermined range.

  According to the fuel gas supply system, the fuel gas supply method, and the marine vessel of the above-described embodiment, when the pressurized boil-off gas is supplied to the engine as the fuel gas, the composition ratio of the boil-off gas changes due to the use of the boil-off gas liquefier. Even when the boil-off gas is supplied under such usage conditions, the voice-off gas pressurized to a predetermined pressure can be stably supplied to the engine.

FIG. 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 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. It is a figure showing an example of the desirable modification of the fuel gas supply system of this embodiment. FIG. 9 is a diagram illustrating an example of a configuration of a fuel gas supply system according to a second embodiment.

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

<First embodiment>
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 first 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, when the composition ratio of the boil-off gas in the pressurizing mechanism and the liquefaction apparatus changes, the boil-off gas in the pressurizing mechanism and the liquefaction apparatus is stored in a tank. In order to replace the boil-off gas vaporized from the liquefied gas with the boil-off gas (fresh boil-off gas before the change in the composition ratio), the boil-off gas having the changed composition ratio is controlled to flow into the gas processing device for consumption. For this reason, even when the boil-off gas is supplied including the use condition in which the composition ratio of the boil-off gas is changed by use of the boil-off gas liquefaction apparatus, the boil-off gas having a constant composition ratio can be pressurized by the pressurizing mechanism. Therefore, the voice off gas pressurized to a predetermined pressure can be supplied to the engine stably.

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 a 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 71a is controlled by a control signal sent from the control device 60 to the contact 71b.

(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 selectively 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 of the boat, and a propeller of the boat. 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 so that the main shaft rotation speed of the main shaft connecting the propulsion engine 40 and the propelling propeller becomes the target rotation speed, and controls the pressure 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 tachometer 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 control device 60 controls the amount of boil-off gas delivered by the pressurizing mechanism 30 using the target pressure.

(Liquefaction equipment)
The liquefaction device 50 is connected to the pressurizing mechanism 30 through a branch pipe 51. The branch pipe 51 is connected to the main pipe 31 between the branch point of the bypass pipe 33c from the main pipe 31 and 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. Some of the boil-off gas is not liquefied and maintains the gas. The liquefier 50 joins the boil-off gas with fresh boil-off gas before pressurization, which is vaporized from the liquefied gas in the tank 20 as needed.

The liquefaction apparatus 50 mainly includes a heat exchanger 53, an expansion valve 54, a gas-liquid separator 56, a gas pipe 57, and a liquefied gas pipe 58.
The heat exchanger 53 cools the boil-off gas before liquefying the boil-off gas.
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 gas-liquid separator 56 separates the cooled boil-off gas from the liquefied gas.
The gas pipe 57 vaporizes the boil-off gas separated from the liquefied gas from the liquefied gas in the tank 20 and joins the boil-off gas with fresh boil-off gas which is taken out of the tank 20 and flows.
The liquefied gas pipe 58 allows the liquefied gas separated by the gas-liquid separator 56 to flow into the tank 20.

  The branch pipe 51 between the heat exchanger 53 and the expansion valve 54 is provided with a control valve 55a for controlling the amount of boil-off gas flowing through the liquefier 50. The gas-liquid separator 56 includes a gas-liquid separator 56. A pressure gauge 56a for measuring the pressure of the boil-off gas in 56 is provided. The opening of the control valve 55a is adjusted based on the measurement result of the pressure gauge 56a. Specifically, the measurement result of the pressure gauge 56a is sent to the control device 60, and the control device 60 generates a control signal for controlling the opening of the control valve 55a based on the measurement result of the pressure gauge 56a. The signal is sent to the control valve 55a.

  The gas pipe 57 is provided with a merge control valve 57a and a pressure gauge 57b for measuring the pressure of the boil-off gas. The opening of the junction control valve 57a is adjusted based on a control signal generated based on the measurement result of the pressure gauge 56b or a control signal sent from the control device 60 to the contact 57d. At this time, a control signal having a low target opening is selected from a control signal indicating the target opening generated based on the measurement result of the pressure gauge 56b and a control signal indicating the target opening sent from the contact 57d. , A selector 57c for sending to the merge control valve 57a is used. In FIG. 1, a dotted line connecting between the pressure gauge 56b and the selector 57c is drawn in order to indicate that the opening of the merge control valve 57a is controlled based on the measurement result of the pressure gauge 56b. Specifically, the measurement result of the pressure gauge 56b is sent to the control device 60, and the control device 60 generates a control signal for the opening degree of the merge control valve 57a based on the sent measurement result, and transmits this control signal to the contact 57d. Send to

  The gas-liquid separator 56 is provided with a liquid level meter 56b for measuring the liquid level of the liquefied gas. The liquefied gas pipe 58 is provided with a recovery control valve 58a, and the amount of liquefied gas flowing through the liquefied gas pipe 58 is controlled by the opening of the recovery control valve 58a. The opening of the recovery control valve 58a is controlled based on the result of measurement of the liquid level by the liquid level meter 56b so that the liquid level falls within a predetermined range.

(Change in composition ratio of boil-off gas and its response)
In such a fuel gas supply system 10, by controlling the opening degree of each of the above-described adjustment valves and control valves, the supply amount of the boil-off gas sent out by the pressurizing mechanism 30, the consumption amount of the propulsion engine 40, Various control states occur between the amount of boil-off gas consumed by the gas treatment device 70 and the amount of liquefied gas generated by the liquefaction device 50 collected in the tank 20. These control states include at least the following control states 1A, 1B, and 2.
(Control state 1A) Boil-off gas supply amount = consumption amount of propulsion engine X1 + consumption amount Y1 of gas processing device, recovery amount Z1 = 0
(Control state 1B) Supply amount of boil-off gas = Consumption amount of propulsion engine X2 (<X1) + Consumption amount of gas processing device Y2 + Recovery amount Z2 (> 0)
(Control state 2) Boil-off gas supply amount = propulsion engine consumption amount X3 (<X2) + gas treatment device consumption amount Y3 (> Y2) + recovery amount Z3 (<Z2), propulsion engine consumption amount X3 = 0.
Including the state of.
In control state 1A, control state 1B, and control state 2, the supply amount of the boil-off gas of the pressurizing mechanism 30, the consumption amount of the propulsion engine 50, the consumption amount of the gas processing device 70, and the recovery amount in the liquefaction tank 20 are all shown. Is the control state (steady state) that is equal to the total amount. The control state 1A and the control state 1B are referred to as control state 1 when generically described.

  In the above control state 1A, the boil-off gas supply amount is equal to the total amount of the boil-off gas consumption amount X1 of the propulsion engine 40 and the total amount of the boil-off gas consumption amount Y1 of the gas processing device 70. , The control valves 55a, 57a, 58a are closed, that is, the control state in which the recovery amount Z1 is set to 0.

In the control state 1B, the supply amount of the boil-off gas is larger than the total amount of the consumption amount X2 of the boil-off gas of the propulsion engine 40 and the consumption amount Y2 of the boil-off gas of the gas processing device 70, and the difference is collected in the tank 20. That is, a control state in which the control valve 55a is opened so that the liquefied gas generated by liquefaction of the boil-off gas is collected in the tank 20. In this control state, in addition to the liquefied gas, boil-off gas not liquefied by the function of the expansion valve 54 flows into the gas-liquid separator 66. At this time, the recovery control valve 58a is opened to direct the liquefied gas to the tank 20. At the same time, the boil-off gas is vaporized from the liquefied gas in the tank 20 and joined to the fresh unpressurized boil-off gas flowing through the main pipe 31 by opening the merge control valve 57a. In this control state 1B, the consumption amount Y2 of the gas processing device 70 is adjusted so that the pressure of the boil-off gas in the tank 20 is located in a predetermined range, that is, the opening degree of the gas processing control valve 71a is adjusted. You.
Thus, in the control state 1B, the supply amount of the boil-off gas of the pressurizing mechanism 30 is larger than the total amount of the consumption amount X2 of the propulsion engine 40 and the consumption amount Y2 of the gas processing device 70, and this difference is stored in the tank 20. By setting the recovery amount Z2 of the liquefied gas to be recovered, a steady state is established.

  In the control state 1B, while the liquefied gas liquefied from the boil-off gas among the boil-off gases is collected in the tank 20, the unliquefied boil-off gas circulates in the pressurizing mechanism 30 and the liquefaction apparatus 50. Is continued for a long time, the composition ratio of the boil-off gas pressurized by the pressurizing mechanism 30 changes with time. That is, the boil-off gas that joins the fresh boil-off gas before pressurization flowing through the main pipe 31 drawn from the tank 20 from the liquefaction device 50 through the merge control valve 57a is not liquefied separated from the liquefied gas by the liquefaction device 50. This is a boil-off gas, and the ratio of components having a low boiling point in 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 liquefier 50 increases to 10% or more when the control state 1B is maintained for a long time. As the ratio of nitrogen increases, the amount of liquefied gas recovered to the tank 20 through the recovery control valve 58a 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. 2 is a diagram illustrating 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 many components having a low boiling point is larger than that of the boil-off gas containing no components 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).

For this reason, in the present embodiment, the boil-off gas in which the ratio of the component having a lower boiling point is higher than the main component circulating through the pressurizing mechanism 30, the liquefaction device 50, and the main pipe 31 is concentrated in the gas treatment device 70. To replace the liquefied gas in the tank 20 with fresh boil-off gas vaporized. Control state 2 performs this replacement. For this reason, the control state 2 is implemented temporarily or intermittently.
Therefore, to achieve the control state 2, the consumption of the boil-off gas of the gas processing device 70 is increased as compared with the control state 1B.

  In control state 2, the consumption amount of boil-off gas X3 = 0 by the propulsion engine 40 after the propulsion engine 40 stops (the supply amount of boil-off gas to the propulsion engine 40 is 0), and the consumption amount Y3 of the gas treatment device 70 ( > Y2) and the recovery amount Z3 of the liquefied gas to the tank 20 coincide with the supply amount of the boil-off gas. At this time, the consumption amount Y3 of the gas processing device 70 is controlled to be larger than the consumption amount Y2 in the control state 1B, and the collection amount Z3 of the liquefied gas to the tank 20 is set to be smaller than the collection amount Z2 in the control state 1B. It is in a controlled state. Specifically, the boil-off gas having a changed composition ratio in the pressurizing mechanism 30 and the liquefaction apparatus 50 is combined with the fresh boil-off gas vaporized from the liquefied gas in the tank 20 flowing through the main pipe 31 through the gas pipe 57. This is a control state in which the gas is consumed by the gas processing device 70. Therefore, the consumption Z3 of the gas processing device 70 is larger than the consumption Z2 of the gas processing device 70 in the control state 1B. Therefore, the control device 60 realizes the control state 2 by increasing the opening of the gas processing control valve 71a as compared with the control state 1. At this time, as the amount of boil-off gas consumed by the gas processing device 70 increases, the opening of the control valve 55a is reduced to reduce the amount of boil-off gas flowing to the liquefaction device 50.

  The liquefaction apparatus 50 is provided with the merging control valve 57a for controlling the amount of the boil-off gas, which is maintained without being liquefied among the boil-off gases, and is combined with the flow of the boil-off gas flowing out of the tank 20, so that the control state 2 is realized. can do.

At this time, the opening degree of the merge control valve 57a in the control state 2 is made smaller than that in the control state 1 (for example, the control state 1B) in the same manner as the opening degree of the recovery control valve 58a, so that the gas-liquid separator 56 This is preferable in that the ratio between the liquefied gas and the boil-off gas inside can be kept at an appropriate level, and stable gas-liquid separation can be realized.
As described above, the control device 60 is configured to switch the flow of the boil-off gas between the control state 1 and the control state 2.
The control state 1 controls the opening degree of the gas processing control valve 71a, so that the total amount of the consumption amount of the boil-off gas by the propulsion engine 40 and the gas processing device 70 and the collection amount of the liquefied boil-off gas in the tank 20 are obtained. This is a control state in which the supply amount of the boil-off gas sent out by the pressurizing mechanism 30 is matched. In the control state 2, the supply of the boil-off gas to the propulsion engine 40 is stopped, the opening of the gas processing control valve 71a is made larger than the opening of the gas processing control valve 71a in the control state 1, and the recovery control valve is set. This is a control state in which the opening degree of the collection control valve 58a is smaller than the opening degree of the collection control valve 58a in the control state 1. Therefore, when it is determined that the composition ratio of the boil-off gas has changed, the boil-off gas in the pressurizing mechanism 30 and the liquefier 50 can be intensively consumed by the gas processing device 70. Therefore, even when the use condition of changing the composition ratio of the boil-off gas by the use of the boil-off gas liquefaction device is included, the voice-off gas pressurized to a predetermined pressure is stabilized at the start of the reuse of the boil-off gas of the propulsion engine 40. And supplied to the propulsion engine 40.

  In this case, as described above, the control state 1 includes the control state 1A in which the merge control valve 57a is closed (static state 1) and the control state 1B in which the merge control valve 57a is open (static state 2). . In order to realize the control state 2, the control device 60 preferably performs control for switching from the control state 1B (statically set state 2) to the control state 2. In the control state 1B, in the boil-off gas joining the main pipe 31 from the liquefaction apparatus 50, the ratio of the component having a low boiling point increases with time. For this reason, by shifting from the control state 1B to the control state 2, the boil-off gas in the pressurizing mechanism 30 and the liquefaction device 50 in which the ratio of the component having a low boiling point has increased can be consumed by the gas processing device 70. Thereby, the boil-off gas in the pressurizing mechanism 30 and the liquefier 50 is easily converted into fresh boil-off gas having a low ratio of components having a low boiling point (vaporized from the liquefied gas in the tank 20 and not passed through the liquefier 50). Can be replaced by In the control state 2, since the boil-off gas in the pressurizing mechanism 30 and the liquefaction device 50 in which the ratio of the component having a low boiling point is increased is consumed by the gas processing device 70, the gas processing device 70 (and the propulsion engine 40) is used. Of the boil-off gas per unit time consumed in the above, information on the amount of the boil-off gas stored in the pressurizing mechanism 30 and the liquefaction device 50, and the amount of the fresh boil-off gas vaporized from the liquefied gas in the tank 20 The duration of the control state 2 may be determined based on the information on the ratio of the amount of the boil-off gas that joins the fresh boil-off gas through the gas pipe 57. The information on the amount of the boil-off gas stored in the pressurizing mechanism 30 and the liquefier 50 is, for example, a total weight obtained by multiplying the volume occupied by the boil-off gas and the liquefied gas in the pressurizer 30 and the liquefier 50 by the density. can get.

  The change in the composition ratio of the boil-off gas may be determined, for example, by periodically measuring the composition ratio of the boil-off gas with a measuring device. The determination may be performed using the information on the compression characteristic shown in FIG. 1, and the determination method is not particularly limited in the present embodiment.

  Hereinafter, the flow of the boil-off gas and the change in the state of the control valve regarding the transition from the control state 1A to the control state 1B and the transition from the control state 1B to the control state 2 will be described using a table. In the transition state between the control states, the total amount of the supply amount of the boil-off gas, the consumption amount of the propulsion engine, the consumption amount of the gas processing device, and the collection amount of the liquefied gas is not always the same. Table 1 shows an example of a change in each flow rate and a change in the opening of the control valve. In the table, “⇒” indicates a state transition, and “↑” indicates that the flow rate increases or the control valve opening increases as the state advances in the direction of “⇒”. "↓" indicates that the flow rate decreases or the control valve opening decreases as the state advances in the direction of "⇒". “〜 →” in the table means that the opening slightly fluctuates during the transition of the state, but does not finally change largely and is substantially maintained. Further, the flow rate in the table indicates a flow rate per unit time, and is indexed with the amount of boil-off gas generated from the tank 20 as 100. In Tables 1, 2A, and 2B, the transition from the control state 1A to the control state 1B and the transition from the control state 1B to the control state 2 are shown, but the transition from the control state 2 to the control state 1B, and the transition from the control state 1B. The transition to the control state 1A may be reversed from the states shown in Tables 1, 2A, and 2B.

  As described above, in the present embodiment, the control states 1A, 1B, and 2 can be realized by controlling the opening of each control valve.

  In the present embodiment, as shown in FIG. 3, a determination device 80 that determines whether or not there is a change in the composition ratio of the boil-off gas pressurized by the pressurizing mechanism 30 is provided. Is determined, the determination result is sent to the control device 60, and the control device 60 preferably controls the opening of each control valve so as to switch from the control state 1B to the control state 2. FIG. 3 is a diagram illustrating an example of a preferred modification of the fuel gas supply system 10.

  For example, in the control state 1, the determination device 80 can determine a change in the composition ratio of the boil-off gas based on information on the opening of the adjustment valves 34a, 34c, and 34e, for example, a value of a control signal for controlling the opening. preferable. This determination utilizes the compression characteristics shown in FIG. 2, that is, changes in the compression characteristics of the boil-off gas, in which the pressure after compression changes when the composition ratio changes even with the same volume of compression. In this case, it is highly likely that the determination device 80 determines that the composition ratio of the boil-off gas has changed when the information of the opening degree, for example, the value of the control signal of the opening degree changes over time and falls outside a predetermined range. It is preferable from the viewpoint of realizing the determination accuracy. When the ratio of the component having a low boiling point in the boil-off gas increases, the pressure of the boil-off gas pressurized by the gas compressors 32a to 32e increases as shown in FIG. In order to maintain the pressure within a predetermined range, the opening of the regulating valves 34a, 34c, 34e must be increased to increase the amount of boil-off gas flowing through the bypass pipes 33a, 33c, 33e. Therefore, the determination device 80 can determine the change in the composition ratio of the boil-off gas based on the information on the opening degrees of the adjustment valves 34a, 34c, and 34e in the control state 1 that is a steady state.

  It is also preferable that the determination device 80 determines a change in the composition ratio of the boil-off gas based on, for example, energy consumed per unit time consumed by the pressurizing device in the control state 1 to pressurize the boil-off gas. This determination also utilizes the change in the compression characteristic of the boil-off gas, as shown in FIG. 2, in which the pressure after compression changes when the composition ratio changes even with the same volume of compression. In this case, it is also preferable that the determination device 80 determine that the composition ratio of the boil-off gas has changed when the consumed energy changes over time and goes out of the predetermined range, from the viewpoint of achieving high determination accuracy. When the ratio of the component having a low boiling point in the boil-off gas increases, the pressure of the boil-off gas compressed by the gas compressors 32a to 32e increases, so that the energy consumption for driving the gas compressors 32a to 32e increases. For this reason, the determination device 80 can determine a change in the composition ratio of the boil-off gas based on the energy consumption for driving the gas compressors 32a to 32e in the control state 1 which is a steady state.

<Embodiment 2>
FIG. 4 is a diagram illustrating an example of another configuration of the fuel gas supply system 10 according to the second embodiment.
The fuel supply system shown in FIG. 4 differs in a part of the configuration of the liquefaction device 50 and the gas processing device 70. Since other configurations are the same, the same reference numerals are given to the same components as those of the fuel gas supply system 10 shown in FIG. 1, and the description of the configuration and functions is omitted. In FIG. 4, the pressure gauge 57b, the selector 57c, and the contact 57d are omitted for the sake of simplicity.

The liquefaction apparatus 50 shown in FIG. 4 is a pipe connected to the branch pipe 39 connected to the gas processing apparatus 70 so that the boil-off gas of the boil-off gas, which is maintained without being liquefied, flows toward the gas processing apparatus 70. 59 is provided. Thus, the boil-off gas not liquefied by the liquefaction device 50 can be quickly consumed by the gas processing device 70 without being pressurized by the pressurizing mechanism 30. The pipe 59 connects the gas-liquid separator 56 and the branch pipe 59.
The branch pipe 39 connected to the gas processing device 70 is provided with a control valve 71c and a pressure gauge 71d. The control valve 71c controls the opening based on the measured pressure measured by the pressure gauge 71d so that the amount of the boil-off gas flowing toward the gas processing device 70 does not become excessive.
In this case, the boil-off gas flowing through the pipe 59 connected to the branch pipe 39 of the liquefier 50 is heated by exchanging heat with the high-temperature boil-off gas before liquefaction flowing from the pressurizing mechanism 30 to the liquefier 50 to perform heat exchange. The vessel 53b is preferably provided in the pipe 59. Thereby, the boil-off gas cooled by expansion by the expansion valve 54 of the liquefaction device 50 can be heated to a temperature suitable for consumption by the gas processing device 70.

  In the fuel gas supply system 10 as well, as in the first embodiment, the control device 60 can switch the control state between the control state 1 and the control state 2, so that the composition ratio of the boil-off gas has changed. Is determined, the boil-off gas in the pressurizing mechanism 30 and the liquefaction device 50 can be intensively consumed in the gas processing device 70. Therefore, even when the use condition of changing the composition ratio of the boil-off gas by the use of the boil-off gas liquefaction device is included, the voice-off gas pressurized to a predetermined pressure is stabilized at the start of the reuse of the boil-off gas of the propulsion engine 40. And supplied to the propulsion engine 40.

In such a fuel gas supply system, the following fuel gas supply method can be performed.
That is, the fuel gas supply method is
(1) In order to supply the vaporized boil-off gas from the tank 20 storing the liquefied gas to the propulsion engine 40 as a fuel gas, the pressurizing mechanism 30 pressurizes (compresses) the boil-off gas vaporized from the liquefied gas as the fuel gas. Sending,
(2) a process in which a part of the pressurized boil-off gas is used as a fuel in the gas processing device 70;
(3) liquefying a part of the pressurized boil-off gas and collecting it in the tank 20;
including.
At this time,
(4) The boil-off flow is switched between the control state 1 and the control state 2 by the control device 60.
The control state 1 controls the amount of the boil-off gas flowing to the gas processing device 70, and thus the total amount of the consumption of the boil-off gas by the propulsion engine 40 and the gas processing device 70 and the amount of the liquefied boil-off gas collected in the tank 20. And a control state in which the supplied amount of the supplied boil-off gas is matched.
In the control state 2, the supply of the boil-off gas to the propulsion engine 40 is stopped, the consumption of the boil-off gas by the gas processing device 70 is increased compared to the consumption of the boil-off gas by the gas processing device 70 in the control state 1, and , A control state in which the amount of boil-off gas recovered to the tank 20 is smaller than the amount of boil-off gas recovered to the tank 20 in the control state 1.

  Further, in the control state 2, the amount of the boil-off gas, which is maintained without being liquefied among the boil-off gases, being combined with the flow of the boil-off gas flowing out of the tank 20 may be reduced as compared with the control state 1. This is preferable in that the ratio between the liquefied gas and the boil-off gas in the liquid separator 56 can be kept at an appropriate level and stable gas-liquid separation can be realized.

  The control state 1 includes a control state 1A (static state 1) in which the boil-off gas of which the gas is maintained without being liquefied is not merged with the flow of the boil-off gas flowing out of the tank 20; It includes a control state 1B (static state 2) in which the boil-off gas in which the gas is maintained without being liquefied is combined with the flow of the boil-off gas flowing out of the tank 20. At this time, it is preferable that the control device 60 performs control so that the control state 2 is switched from the statically set state 2.

  Further, when a change in the composition ratio of the boil-off gas pressurized by the pressurizing mechanism 30 occurs, the control device 60 preferably performs control so as to switch from the control state 1 to the control state 2.

  It is preferable that the determination device 80 determines the change in the composition ratio of the boil-off gas in the control state 1 based on information on the opening of the regulating valves 34a, 34c, and 34e, for example, a value of a control signal for controlling the opening. . At this time, it is preferable that the determination device 80 determines that the composition ratio of the boil-off gas has changed when the opening degree changes with the elapsed time and falls outside a predetermined range.

  The determination device 80 performs the boil-off based on the energy consumed per unit time consumed by the gas compressors 32a to 32e of the pressurizing mechanism 30 in the control state 1 (for example, the control state 1B) for pressurizing the boil-off. It is preferable to determine a change in the gas composition ratio. In this case, when the consumed energy changes with the elapsed time and goes out of the predetermined range, the determination device 80 preferably determines that the composition ratio of the boil-off gas has changed.

  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 31a to 31d check valves 32a to 32e gas compressors 33a, 33c, 33e bypass pipes 34a, 34c, 34e, 55a adjustment valves 35a to 35e suction snubbers 36a to 36e discharge Snubbers 37a to 37e Heat exchangers 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 55a Control valve 56 Gas-liquid Separator 56a, 71d Pressure gauge 56b Liquid level gauge 57 Gas pipe 57a Merging control valve 57b Pressure gauge 57d, 71b Contact 58 Liquefied gas pipe 58a Recovery control valve 60 Control unit 62 Engine control unit 70 Gas processing unit 71a Gas processing control bar Lube 71c Control valve 80 Judgment device

Claims (19)

A fuel gas supply system that supplies fuel gas to an engine,
A tank for storing liquefied gas,
A pressurizing mechanism that pressurizes and sends out the boil-off gas vaporized from the liquefied gas as fuel in order to supply the boil-off gas vaporized from the liquefied gas as a fuel gas to an engine,
An apparatus for liquefying a part of the boil-off gas which is pressurized and sent out by the pressurizing mechanism, and controls a quantity of the liquefied gas to be collected in the tank among liquefied gases generated by liquefaction of the boil-off gas. A liquefaction device comprising a control valve;
A gas that is 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 as a fuel, and controls an amount of the boil-off gas flowing through the branch pipe toward the gas processing device. A process control valve;
A control device that adjusts the opening of the recovery control valve and the gas processing control valve,
The control device, by controlling the opening degree of the gas treatment control valve, the total amount of consumption of boil-off gas by the engine and the gas treatment device and the amount of liquefied boil-off gas collected in the tank, The control state 1 in which the supply amount of the boil-off gas sent out by the pressurizing mechanism is made to match, and the supply of the boil-off gas to the engine is stopped, and the opening degree of the gas processing control valve is changed to the gas processing in the control state 1. The boil-off flow is switched between a control state 2 in which the opening degree of the recovery control valve is made larger than the opening degree of the control valve and an opening degree of the recovery control valve is made smaller than the opening degree of the recovery control valve in the control state 1. A fuel gas supply system, characterized in that: The liquefaction device is a merging control valve that controls the amount of boil-off gas that is not liquefied by the liquefaction device and that is vaporized from the liquefied gas and merged with the boil-off gas before being pressurized by the pressurizing mechanism. With
2. The fuel gas supply system according to claim 1, wherein the control device makes the opening of the merge control valve smaller in the control state 2 than in the control state 1. 3. The control state 1 includes a static state 1 in which the merge control valve is closed, and a static state 2 in which the merge control valve is open,
3. The fuel gas supply system according to claim 2, wherein the control device performs control for switching from the stationary state 2 to the control state 2. 4. Further, a determination device for determining whether there is a change in the composition ratio of the boil-off gas pressurized by the pressurizing mechanism,
The fuel gas supply system according to any one of claims 1 to 3, wherein the control device switches from the control state 1 to the control state 2 when the determination device determines a change in the boil-off gas generation ratio. The pressurizing mechanism is a pressurizing device that pressurizes the boil-off gas, and a pipe through which the boil-off gas flows before and after pressurization by the pressurizing device, a bypass pipe connected around the pressurizing device, An adjustment valve for controlling the amount of boil-off gas flowing through the bypass pipe so that the pressure of the boil-off gas after pressurization by the pressurizing device falls within a predetermined range,
The fuel gas supply system according to claim 4, wherein the determination device determines a change in the composition ratio of the boil-off gas based on the information on the opening degree of the adjustment valve in the control state 1.   The fuel gas supply system according to claim 5, wherein the determination device determines that the composition ratio of the boil-off gas has changed when the opening degree changes with the lapse of time and falls outside a predetermined range.   5. The determination device according to claim 4, wherein the determination device determines a change in the composition ratio of the boil-off gas based on energy consumed per unit time consumed by the pressurizing mechanism in the control state 1 to pressurize the boil-off gas. Fuel gas supply system.   The fuel gas supply system according to claim 7, wherein the determining device determines that the composition ratio of the boil-off gas has changed when the consumed energy changes with time and goes out of a predetermined range.   The liquefaction apparatus includes a pipe connected to the branch pipe connected to the gas processing apparatus so that a boil-off gas that maintains a gas without being liquefied among the boil-off gas flows toward the gas processing apparatus. Item 9. The fuel gas supply system according to any one of Items 1 to 8.   The liquefier, a heat exchanger that raises the temperature of boil-off gas flowing through the pipe connected to the branch pipe by heat exchange with boil-off gas before liquefaction flowing from the pressurizing mechanism to the liquefier, The fuel gas supply system according to claim 9. 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,
Pressurizing and delivering the boil-off gas vaporized from the liquefied gas as fuel to supply the boil-off gas vaporized from the tank storing the liquefied gas to the engine as fuel gas;
Processing a part of the pressurized boil-off gas as a fuel in a gas processing device;
Liquefying a part of the pressurized boil-off gas and collecting it in the tank.
By controlling the amount of boil-off gas flowing to the gas treatment device, the total amount of boil-off gas consumption by the engine and the gas treatment device and the amount of liquefied boil-off gas collected in the tank, The control state 1 in which the gas supply amounts are made equal to each other, and the supply of the boil-off gas to the engine is stopped, and the consumption amount of the boil-off gas by the gas processing apparatus is reduced by the consumption amount of the boil-off gas by the gas processing apparatus in the control state 1. And switching the boil-off gas flow between control states 2 in which the amount of boil-off gas recovered to the tank is smaller than the amount of boil-off gas recovered to the tank in the control state 1. A fuel gas supply method comprising:   13. The control state according to claim 12, wherein, in the control state 2, the amount of the boil-off gas, which has been maintained without being liquefied among the boil-off gases, combined with the flow of the boil-off gas flowing out from the tank is smaller than that in the control state 1. The fuel gas supply method as described above. The control state 1 is a stationary state 1 in which the boil-off gas of the boil-off gas, the gas of which is maintained without being liquefied, is not combined with the flow of the pre-pressurized boil-off gas vaporized from the liquefied gas. A boil-off gas in which the gas is maintained without being liquefied, and a statically-set state 2 in which the boil-off gas is vaporized from the liquefied gas and merges with the flow of the boil-off gas before pressurization,
14. The fuel gas supply method according to claim 12, wherein the control state 2 is switched from the static state 2.   The fuel gas supply method according to any one of claims 12 to 14, wherein the control state 1 is switched to the control state 2 when a change in the composition ratio of the boil-off gas occurs. A pressurizing mechanism for pressurizing the boil-off gas is connected between a pressurizing device for pressurizing the boil-off gas and a pipe through which the boil-off gas flows before and after pressurization by the pressurizing device, bypassing the pressurizing device. And a regulating valve for controlling the amount of boil-off gas flowing through the bypass pipe so that the pressure of the boil-off gas after pressurization by the pressurizing device falls within a predetermined range,
16. The fuel gas supply method according to claim 15, wherein a change in the composition ratio of the boil-off gas is determined in the control state 1 based on information on an opening degree of the adjustment valve.   17. The fuel gas supply method according to claim 16, wherein when the opening degree changes with the lapse of time and falls outside a predetermined range, it is determined that the composition ratio of the boil-off gas has changed.   The fuel gas supply method according to claim 15, wherein a change in the composition ratio of the boil-off gas is determined based on energy consumed per unit time consumed by the pressurizing device in the control state 1 to pressurize the boil-off gas.   19. The fuel gas supply method according to claim 18, wherein when the consumed energy changes with the lapse of time and falls outside a predetermined range, it is determined that the composition ratio of the boil-off gas has changed.

Images