JP2018071475A - Fuel gas supply system, vessel and fuel gas supply method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel gas supply system, a fuel gas supply method and a vessel adapted to prevent use of a boil-off gas liquefier from causing a fluctuation in a composition ratio of boil-off gas when pressurized boil-off gas is supplied to an engine as fuel gas.SOLUTION: A fuel gas supply system which supplies fuel gas to an engine comprises: a tank to store liquefied gas; a pressurization mechanism which pressurizes the boil-off gas vaporized from the liquefied gas and delivers the same to the engine as a fuel; a liquefier which liquefies a portion of the boil-off gas pressurized and delivered by the pressurization mechanism and returns the liquefied boil-off gas to the tank; and a control device which controls an amount of the boil-off gas flowing in the liquefier. The liquefier has recovery piping which returns gas-liquid mixed fluid, a mixture of the liquefied gas liquefied in the liquefier with the boil-off gas not liquefied therein, to a liquid phase of the liquefied gas in the tank.SELECTED DRAWING: Figure 1

Description

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

  In the LNG carrier, boil-off gas naturally evaporated from the liquefied gas stored in the 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 an engine fuel gas. For this reason, in a fuel gas supply system that supplies boil-off gas as engine fuel gas, a fuel gas such as boil-off gas is compressed using a compression device, for example, a multistage compression device. The compressed fuel gas is sent out to the engine.
On the other hand, the consumption of fuel gas in the engine may change due to load fluctuations. In this case, in order to effectively recover the excess compressed boil-off gas, the boil-off gas is liquefied and returned to the tank.

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

JP2015-505941A

  In the fuel gas supply system, when the boil-off gas is liquefied, there is a boil-off gas that is not liquefied and maintains the gas in addition to the liquefied boil-off gas. This boil-off gas is combined with a flow of fresh boil-off gas (hereinafter also simply referred to as fresh boil-off gas) that has been vaporized from the liquefied gas in the tank to be compressed and supplied to the engine. At this time, the boil-off gas is not a single component but a mixed gas, and includes a component having a high boiling point and a component having a low boiling point. This component having a low boiling point is likely to remain as a gas in the boil-off gas that is not liquefied and maintains the gas. For this reason, the boil-off gas in which the gas is not liquefied and maintains the gas 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 liquefaction treatment but has not been liquefied and maintained gas has more components with lower boiling points than fresh boil-off gas. For this reason, when the boil-off gas that has not been liquefied and maintains the gas is merged with the fresh boil-off gas, the composition ratio of the boil-off gas supplied to the compressor changes. For example, natural gas may contain several percent of nitrogen having a lower boiling point than methane in addition to methane. In addition, liquefied ethane may contain several percent of methane ga, which has a lower boiling point than ethane. In this case, since the boil-off gas that circulates between the compression device and the liquefaction device is repeatedly subjected to liquefaction treatment, the content of low-boiling components in the boil-off gas increases with time. For example, in the case of natural gas The content of nitrogen contained in the boil-off gas exceeds 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 is obtained 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 delivered by controlling the pressure. Becomes difficult.

  When the fuel gas supply system is applied to a ship, when the ship waits for cargo handling, waiting for a canal, or the like, the propulsion engine is stopped and the liquefaction device is driven to the maximum to liquefy and collect the boil-off gas. If this state continues for a long time, the composition ratio of the boil-off gas will change significantly. As a result, the boil-off gas cannot be used effectively as a fuel gas due to a decrease in the amount of heat as fuel gas, changes in ignition conditions, changes in combustion, etc. . Further, in the design of the compression apparatus, it becomes difficult to cope with a change in flow rate and a temperature change during compression of the boil-off gas due to a change in the composition ratio of the boil-off gas. In addition, a change in the composition ratio of the boil-off gas caused by the liquefaction device similarly reduces the liquefaction efficiency even on land bases storing natural gas. Equipment for removing nitrogen from natural gas (for example, selectively removing nitrogen gas by using a difference in boiling point) is also being studied. However, such equipment is complex and not practical for use on ships. In addition, since the load of the ship's propulsion engine changes frequently and is not constant, it is difficult to use the above equipment, and it is not easy to start the equipment, and operation maintenance of the equipment is required.

  Therefore, the present invention provides a fuel gas supply system configured to prevent the composition ratio of the boil-off gas from being changed by using a boil-off gas liquefier when a pressurized boil-off gas is supplied to the engine as a fuel gas. The object is to provide a method and a ship.

One embodiment of the present invention is a fuel gas supply system that supplies fuel gas to an engine.
The fuel gas supply system is
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 as a fuel gas to the engine;
A liquefaction device for liquefying a part of the boil-off gas sent by being pressurized by the pressurization mechanism and returning it to the tank;
A control device for controlling the amount of boil-off gas flowing to the liquefying device;
Is provided.
The liquefier includes a recovery pipe that returns a gas-liquid mixed fluid of the liquefied gas liquefied by the liquefier and the boil-off gas that has not been liquefied into the liquid phase of the liquefied gas in the tank.

  The recovery pipe is preferably provided with a cooling device for cooling the gas-liquid mixed fluid.

The fuel gas supply system further includes:
Gas processing control that is provided in a branch pipe connected to a gas processing apparatus that consumes a part of the boil-off gas pressurized by the pressurizing mechanism and controls the amount of boil-off gas that flows 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 liquefying device.
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 in accordance with the pressure of the boil-off gas in the tank. It is preferable to do.

  The control device opens the liquefaction control valve when the sum of the consumption amount of voice off gas of the engine and the consumption amount of boil off gas of the gas processing device is smaller than the supply amount of boil off of the pressurizing mechanism. It is preferable to control.

  In the control device, it is preferable that the opening speed of the liquefaction control valve increases continuously or stepwise as time passes.

  The control device has a flow rate of 20% of the optimum recovered gas amount, which is the maximum boil-off gas flow rate at which the boil-off gas can be liquefied most by the liquefaction device from the start of opening of the liquefaction control valve. It is preferable to control the opening degree of the liquefaction control valve so that the time until it reaches 1 is 1 minute or more.

  When the control device opens the liquefaction control valve, the control device changes the pressure of the boil-off gas in the tank from the gas processing control state in which the opening of the gas processing control valve is controlled according to the pressure of the boil-off gas in the tank. Accordingly, 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 opening degree of the liquefaction control valve is controlled accordingly.

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,
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 for instructing the opening 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;
A gas processing sequence control signal for instructing the opening of the gas processing 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 processing selector,
A liquefaction feedback control signal for instructing the opening of the liquefaction control valve so that the pressure of the boil-off gas in the tank becomes a set liquefaction pressure set value;
The liquefaction sequence control signal for instructing 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, and the selection for liquefaction To the vessel,
The gas processing selector selects a control signal having a larger indication value of the opening from the gas processing feedback control signal and the gas processing sequence control signal, and sends the control signal to the gas processing control valve.
It is preferable that the liquefying 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 selected control signal to the liquefaction control valve.

  The control device is configured such that when the liquefaction control valve is closed, the gas treatment pressure set value is lower than the liquefaction pressure set value, and when the liquefaction control valve is open, the gas treatment pressure set value is the liquefaction pressure. It is preferable to adjust the gas processing pressure setting value and the liquefaction pressure setting value so as to be larger than the setting value.

  The control device controls the liquefaction control by controlling an 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 when the liquefaction control valve is closed. It is preferable to control the opening degree of the liquefaction control valve so that the pressure of the boil-off gas in the tank becomes the liquefaction pressure set value when the valve is open.

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

Yet another embodiment of the present invention is a fuel gas supply method for supplying fuel gas to an engine. The fuel gas supply method is
Pressurizing and sending out the boil-off gas vaporized from the liquefied gas by a pressurizing mechanism to supply the boil-off gas vaporized from the tank storing the liquefied gas as a fuel gas to the engine;
The gas-liquid mixed fluid containing the boil-off gas that has not been liquefied, which is generated by liquefying a part of the pressurized boil-off gas with a liquefier, is returned to the liquid phase of the liquefied gas in the tank. Steps.

  The fuel gas supply method preferably further includes a step of cooling the gas-liquid mixed fluid before returning it to the tank.

The fuel gas supply method further includes a step of flowing toward a gas processing device that consumes a part of the pressurized boil-off gas as fuel,
Either the amount of boil-off gas that flows toward the gas processing device or the amount that returns the gas-liquid mixed fluid 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 total amount of voice-off gas consumed by the engine and the amount of boil-off gas consumed by the gas processing device is smaller than the amount of boil-off supplied by the pressurizing mechanism, the gas-liquid mixed fluid is liquefied gas in the tank. It is preferable to perform the step of returning to the liquid phase.

  When boil-off gas is supplied to the liquefying device to start liquefaction, it is preferable that the amount of boil-off gas supplied to the liquefier is increased continuously or stepwise over time.

  When boil-off gas is supplied to the liquefier and liquefaction is started, the boil-off gas flow rate is 20% of the optimum recovered gas amount, which is the maximum boil-off gas flow rate at which the boil-off gas can be liquefied most by the liquefaction device. It is preferable to control the flow rate of the boil-off gas flowing through the liquefaction device so that the time until the flow rate is reached is 1 minute or longer.

  When the boil-off gas is supplied to the liquefaction device and liquefaction is started, the gas according to 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. According to 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 liquefaction pressure setting value from the gas processing control state for controlling the amount of boil-off gas flowing to the processing apparatus. 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 boil-off gas flowing to the liquefier is controlled.

  According to the fuel gas supply system, fuel gas supply method, and ship of the above aspect, when supplying pressurized boil-off gas to the engine as fuel gas, the composition ratio of the boil-off gas does not change and is pressurized to a predetermined pressure. It is possible to stably supply the voice-off gas to the engine.

It is a figure which shows an example of a structure of the fuel gas supply system of this Embodiment 1. It is a figure which shows the principal part containing the confluence | merging piping of the conventional liquefying apparatus. It is a figure which shows an example of the compression characteristic of boil-off gas which changes with the change of the composition ratio of boil-off gas. (A), (b) is a figure which shows the example of the time change of the pressure in the fuel gas supply system of this embodiment, and the opening degree of a control valve.

  Hereinafter, the fuel gas supply system, ship, and 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. Although liquefied natural gas is used as the liquefied gas of the fuel gas supply system 10, the liquefied natural gas is not limited to liquefied natural gas, and liquefied gas such as pure methane or ethane can be used. The boil-off gas includes, in addition to the gas vaporized by natural heat input in the tank, gas that is forcibly vaporized by intentionally heating LNG. In the present embodiment, description will be made using a gas vaporized by natural heat input in a tank. In the case of using a gas that is forcibly vaporized, a forced vaporizer that vaporizes the boil-off gas from the liquefied gas is provided.

The fuel gas supply system 10 is used to supply boil-off gas evaporated in a tank 20 storing liquefied natural gas to the propulsion engine 40 as fuel gas in an LNG ship 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, respectively.
In this specification, the direction in which the boil-off gas is supplied from the tank 20 to the propulsion engine 40 is referred to as the downstream direction, the opposite direction is referred to as the upstream direction, and the downstream side is referred to as the downstream side from a certain reference position. The upstream side from the position is referred to as the upstream side.

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

The fuel gas supply system 10 of this 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 in the pipe. A pressurizing mechanism 30 is provided on a main pipe 31 through which boil-off gas extending from the tank 20 to the propulsion engine 40 flows.
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 liquefying device 50 is a device that liquefies a portion of the boil-off gas that has been pressurized and sent out by the pressurizing mechanism 30 and collects it in the tank 20.
The control device 60 is a device that controls the flow of the boil-off gas in the fuel gas supply system 10, and is a device that adjusts at least the adjustment valve provided in the pressurizing mechanism 30 and the liquefying device 50, and the opening of the control valve. is there.

(Pressure mechanism)
The pressurizing mechanism 30 includes gas compressors (pressurizing devices) 32a to 32e, bypass pipes 33a, 33c and 33e, adjustment valves 34a, 34c and 34e, suction snubbers 35a to 35e, discharge snubbers 36a to 36e, The heat exchangers 37a to 37e are mainly provided.
Each of the suction snubbers 35a to 35e is provided on the upstream side of each of the gas compressors 32a to 32e. The boil-off gas is temporarily stored, and the boil-off gas is smoothly sucked into each of the gas compressors 32a to 32e. A container having a space. Each of the discharge snubbers 36a to 36e is a container that is provided on the downstream side of each of the gas compressors 32a to 32e, and includes a space configured to temporarily store the boil-off gas and smoothly send out 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 that has become high temperature by being pressurized.

The gas compressors 32a to 32e are multistage pressurizing devices connected in series that pressurize (compress) the boil-off gas and send it out. The gas compressors 32a to 32e are portions that suck the boil-off gas in the suction snubber and pressurize it 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 when a movable part (plunger or piston) in the gas compressors 32a to 32e reciprocates linearly, and then pressurizes it. be able to. Of the gas compressors 32a to 32e, the oil compressors are used as the gas compressors 32a to 32d, and the oil compressor is used as the gas compressor 32e that pressurizes the boil-off gas at a high pressure. 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 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 bypasses the gas compressors 32a and 32b and connects the suction snubber 35a and the output end of the heat exchanger 37b. That is, the part of the pipe through which the boil-off gas before being pressurized by the gas compressor 32a flows and the gas compressor This is a pipe through which boil-off gas flows, connected between pipes through which boil-off gas after pressurization by 32b flows.
The bypass pipe 33c bypasses the gas compressors 32c and 32d and connects the suction snubber 35c and the output end of the heat exchanger 37d, that is, a part of a pipe through which boil-off gas before being pressurized by the gas compressor 32c flows. This is a pipe through which boil-off gas flows, connecting between pipes through which the boil-off gas pressurized by the gas compressor 32d flows.
The bypass pipe 33e bypasses the gas compressor 32e and connects the suction snubber 35e and the output end of the heat exchanger 37e. That is, the bypass pipe 33e is connected to the pipe portion through which the boil-off gas before being pressurized by the gas compressor 32e flows and the gas compressor 32e. It is a pipe through which boil-off gas flows, connected between pipes through which the boil-off gas after pressurization flows.

  The bypass pipes 33a, 33c, 33e are provided with adjustment valves 34a, 34c, 34e for adjusting the opening degree. In addition, each of the bypass pipes 33a, 33c, 33e is provided with pressure gauges 38a, 38c, 38e for measuring the pressure of the boil-off gas pressurized by the gas compressors 32b, 32d, 32e. The pressure gauges 38a, 38c, and 38e need to be provided on the bypass pipes 33a, 33c, and 33e if the pressure of the boil-off gas at the branch point where the bypass pipes 33a, 33c, and 33e branch from the main pipe 31 can be measured. Absent. Each of the adjusting valves 34a, 34c, 34e is provided to be adjusted by pressure information measured by the pressure gauges 38a, 38c, 38e. In FIG. 1, the pressure gauges 38a, 38c, and 38e and the adjustment valves 34a, 34a, 38e, and 38e are shown in order to show that the opening degree of the adjustment valves 34a, 34c, and 34e is controlled based on the pressures measured by the pressure gauges 38a, 38c, and 38e. A dotted line connecting 34c and 34e is drawn. Specifically, information on the measured pressure measured by the pressure gauges 38 a, 38 c, and 38 e is sent to the control device 60. The control device 60 generates a control signal for feedback control that controls the amount of boil-off gas flowing through the bypass pipes 33a, 33c, and 33e based on the difference between the sent measurement pressure and the set pressure, and outputs the control signal. It sends to the adjustment valves 34a, 34c, 33e.

For example, when 1500 kg of boil-off gas is supplied from the upstream side per hour, and the gas compressors 32a and 32b or the gas compressors 32c and 32d or the gas compressor 32e pressurize 2000 kg of boil-off gas per hour and send it downstream. 500 kg of boil-off gas per hour is allowed to flow (reverse flow) through the bypass pipe 33a, the bypass pipe 33c, or the bypass pipe 33e, and is returned to the upstream side of the gas compressors 32a, 32b, the gas compressors 32c, 32d, or the gas compressor 32e. Thus, the opening degree of the adjustment valves 34a, 34c, and 34e provided in the bypass pipes 33a, 33c, and 33e is controlled so that 500 kg of boil-off gas flows per hour. Thereby, the pressure on the downstream side of the gas compressors 32a and 32b, the gas compressors 32c and 32d, or the gas compressor 32e can be adjusted to a predetermined pressure. By adjusting to a predetermined pressure, the boil-off gas flowing from the pressurizing mechanism 30 toward the propulsion engine 40 can be set to the fuel gas pressure and the fuel supply amount required by the propulsion engine 40.
In this embodiment, the bypass pipe 33a is provided so as to bypass the gas compressors 32a, 32b at the same time, and the bypass pipe 33c is provided so as to bypass the gas compressors 32c, 32d at the same time. A bypass pipe that bypasses the path may be provided.

In the pressurizing mechanism 30 of this embodiment, a check valve 31a is provided between the fourth-stage gas compressor 32d and the fifth-stage gas compressor 32e. Oil that flows out of the oil supply type compressor included in the boil-off gas sent from the gas compressor 32e that is an oil supply type compressor to the gas compressor 32d that is an oilless type compressor and the gas compressors 32b and 32c on the upstream side thereof. The check valve 31a is provided in order to prevent impurities such as gas from flowing in and contaminating the gas compressor 32d and the devices such as the gas compressors 32b and 32c located upstream thereof.
A check valve may be provided between the first-stage gas compressor 32a and the second-stage gas compressor 32b, counting from the upstream side.
Further, a check valve 31b is provided on the downstream side 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 33 a branches from the main pipe 31 and a junction point where the bypass pipe 33 c joins 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 will be described later, it is preferable that the boil-off gas can be processed even if the composition ratio of the boil-off gas, for example, the ratio of components 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 air-fuel ratio and the ignition timing can be adjusted to cope with a change in the composition ratio of the boil-off gas. Is preferred. Further, the gas processing device 70 is preferably configured to have a capacity capable of consuming the entire amount of 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 31c so that the boil-off gas flowing to the gas processing device 70 side does not flow back to the pressurizing mechanism 30 side. Further, the branch pipe 39 is provided with a gas processing control valve 71 so as to adjust the amount of boil-off gas processed by the gas processing device 70. In the gas processing control valve 71, the opening degree of the gas processing control valve 71 is controlled based on the measured pressure of the pressure gauge 57b provided in the main pipe 31, which will be described later. Since the installation location of the pressure gauge 57b is a portion 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 boil-off gas. The pressure measured by the pressure gauge 57 a is sent to the control device 60. The pressure control signal 60 generates a control signal for controlling the opening degree 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). This is sent to the control valve 71a.

(Propulsion engine)
The ship used in the present embodiment is provided with a propulsion engine 40. As the propulsion engine 40, for example, a dual fuel engine that can use boil-off gas of liquefied gas as fuel gas and oil such as heavy oil as fuel can be used.
The propulsion engine 40 burns in the combustion chamber using the supplied boil-off gas as fuel gas to extract power, and rotates a main shaft (not shown) and a propeller of the vessel (not shown) that connect the propulsion engine 40 and a propeller of the vessel (not shown). 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 the drive is controlled by the ECU 62. The ECU 62 supplies the fuel gas to the propulsion engine 40 so 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 drive of the propulsion engine 40 is controlled by controlling the opening degree of the pressure control valve 44 provided in the supply line. That is, the ECU 62 determines the load of the propulsion engine 40 so 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 this. It is. The ECU 62 determines the load of the propulsion engine 40 so that the main shaft rotational speed that changes due to changes in natural conditions such as weather, sea state wind, and wave height is maintained at the target rotational speed, as well as operator deceleration, acceleration, turning, etc. The load of the propulsion engine 40 can also be determined according to the operation command value of the propeller rotational speed provided by the instruction. In FIG. 1, in order to represent the above-described control, a dotted line connecting the rotating system 42 and the pressure control valve 44 is simply drawn.
The ECU 62 is configured to set a target pressure on the delivery side of the gas compressor 32e located on the most downstream side based on the determined load and to send this target pressure to the control device 60. This target pressure is the fuel supply pressure that the propulsion engine 40 requires from 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 device)
The liquefying device 50 is connected to the pressurizing mechanism 30 through a branch pipe 51 that branches from between a branch point of the bypass pipe 33c from the main pipe 31 and the check valve 31a.
The liquefying device 50 is a device that returns boil-off gas that has become unnecessary due to fluctuations in the load of the propulsion engine 40 to the tank 20 as liquefied gas. A part of the boil-off gas is not liquefied and maintains a gas. In the present embodiment, the boil-off gas is pumped to the liquefied gas in the tank 20 in a gas-liquid mixed fluid together with the liquefied gas obtained by liquefying the boil-off gas. The liquefying device 50 includes a heat exchanger 53 that cools the boil-off gas before the boil-off gas is liquefied, an expansion valve 54 that expands and liquefies the cooled boil-off gas, and a gas-liquid mixed fluid produced by the expansion valve 54. A recovery pipe 56 for returning to the liquid phase of the liquefied gas and a cooler 58 are mainly provided.
The expansion valve 54 expands and liquefies the cooled boil-off gas. The expansion valve 54 may be a valve that changes in an isenthalpy process such as a JT (Joule Thomson) valve, but is preferably a valve that changes in an isentropy 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, the cooling device 58 that cools the gas-liquid mixed fluid generated by the expansion valve 54 is provided in the recovery pipe 56, so that the gas-liquid mixed fluid can be supplied without adding a large amount of heat to the liquefied gas in the tank 20. This 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 that controls the flow rate of the boil-off gas flowing through the liquefying device 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 boil-off gas in the tank 20, that is, boil-off gas before being pressurized by the pressurizing mechanism 30, in other words, 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 (a liquefaction selector) 57 b 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 called a liquefaction feedback control signal), and sends the control device 60 to the contact 57c. Among the control signals for the opening degree of the liquefaction control valve 55 generated based on the sequence for the liquefaction process of the boil-off gas (hereinafter, this control signal is referred to as a liquefaction sequence control signal), the control with the smaller opening degree is controlled. A low-level selector that selects a signal. 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. The liquefaction feedback control signal is sent to the selector 57b. In FIG. 1, the pressure gauge 57a and the selector 57b are connected with a dotted line for easy understanding. The control device 60 generates an opening degree control signal based on the difference between the pressure measured by the pressure gauge 57a and the liquefied pressure set value so that the pressure of the pressure gauge 57a becomes a preset liquefied pressure set value. It is configured. Specifically, the control device 60 increases the opening of the liquefaction control valve 55 when the pressure measured by the pressure gauge 57a is higher than the liquefaction pressure set value, and the pressure measured by the pressure gauge 57a is greater than the liquefaction pressure set value. When it is low, the liquefaction feedback control signal for reducing the opening degree of the liquefaction control valve 55 is generated. 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, and the selector 57b has a low level (small opening degree). A 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 the liquefaction control valve 55 according to the sequence for 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 71 a 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 (gas processing selector) 71c. The selector 71c includes a control signal for the opening degree of the gas processing control valve 71a generated based on the pressure measured by the pressure gauge 57a (hereinafter, this control signal is referred to as a gas processing feedback control signal), and a contact 71b from the control device 60. Of the opening control signal of the gas processing control valve 71a generated based on the gas processing sequence for the boil-off gas (hereinafter, this control signal is referred to as a gas processing sequence control signal). This is a high-level selector that selects the larger control signal.
As described above, since the 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 with a dotted line for easy understanding. The control device 60 generates an opening degree 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. Is configured to do. 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. When the value is lower than the value, a gas processing feedback control signal for reducing the opening of the gas processing control valve 55 is generated. 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 controls the gas processing according to the sequence for boil-off gas processing regardless of the magnitude of the measured pressure. A gas processing sequence control signal for controlling the opening degree of the valve 71a through the contact 71b is generated.

  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. For this reason, in order to prevent the vaporization of the liquefied gas from increasing in the tank 20 and temporarily increasing the pressure in the tank 20, the speed at which the opening of the liquefaction control valve 55 increases is initially small, The control device 60 controls to increase continuously or intermittently as time passes. Specifically, the liquefaction control valve has a flow rate smaller than the optimum recovered gas amount, which is the maximum boil-off gas flow rate that can be liquefied most by the cooling of the boil-off gas by the heat exchanger 53 and the expansion of the boil-off gas by the expansion valve 54. The opening speed of the liquefaction control valve 55 is initially small so that it flows through the liquefaction device 50 at the beginning of opening of the liquefaction device 55. Thereafter, the controller 60 increases the speed of the opening of the liquefaction control valve 55 continuously or intermittently with time so that the boil-off gas flowing in the liquefier 50 approaches the optimum recovered gas amount. Thus, the opening degree 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 to reach the boil-off gas flow rate of 20% of the optimum recovered gas amount is 1 minute or more. It is preferable.

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

  FIG. 2 is a diagram illustrating the configuration of piping and the like downstream of the expansion valve 54 of the conventional liquefying device 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 liquefied gas and boil-off gas, and the liquefied gas is recovered in the tank 20 by the recovery pipe 156. On the other hand, when the boil-off gas is merged 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. It becomes difficult to control the boil-off gas.

  Of the boil-off gas, the liquefied gas liquefied from the boil-off gas is collected in the tank 20 and the boil-off gas that has not been liquefied circulates in the pressurizing mechanism 30 and the liquefying 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 joins the fresh boil-off gas before pressurization flowing through the main pipe 31 drawn from the tank 20 through the joining pipe 57 is a boil-off gas that has been separated from the liquefied gas by the liquefying device 50 and has not been liquefied. 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 pressurized changes with time. That is, the composition ratio in the boil-off gas of the component having a lower boiling point than the main component of the liquefied 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 lower boiling point than methane or ethane. On the other hand, the ratio of the nitrogen component in the boil-off gas that has passed through the liquefier 50 increases. For example, even when 1% nitrogen is mixed in liquefied natural gas, the nitrogen ratio of the boil-off gas that has passed through the liquefier 50 is controlled for a long time in a control state in which the boil-off gas circulates in the pressurizing mechanism 30 and the liquefier 50. If maintained, increase to 10% or more. As the nitrogen ratio increases, the 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 will be described later. As a result, the amount of boil-off gas flowing through the bypass pipes 33a and 33c gradually increases by adjusting the opening of the adjustment valves 34a and 34c, and finally, it becomes difficult to control the amount of boil-off gas delivered by the pressurizing mechanism 30. .

FIG. 3 is a diagram showing an example of the relationship between the pressure and volume of boil-off gas received in the compression process by the gas compressor. Of the boil-off gas of the liquefied gas, the boil-off gas containing only the main component not including the component having a low boiling point rises from the pressure P1 to the pressure P2 along the path A when being 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 if the boil-off gas is subjected to the same volume change compression process. For this reason, the energy consumed by the gas compressor in the same compression treatment with a boil-off gas containing a component having a low boiling point is larger than that of a boil-off gas not containing a component having a low boiling point.
In this way, by increasing the pressure of the boil-off gas pressurized by the same compression process, the amount (mass) of boil-off gas delivered by the pressurizing mechanism 30 is controlled (bypass pipes 33a, 33c, 33e by the adjusting valves 34a, 34c, 34e). Pressure based control of the amount of boil-off gas flowing through is difficult.

  Therefore, in the present embodiment, the gas-liquid mixed fluid generated by the liquefying device 50 is returned to the liquid phase in the tank 20. For this reason, 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.

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

When the load of the propulsion engine 40 is large and the amount of boil-off gas consumed is large, the sum of the amount of boil-off gas consumed by the propulsion engine 40 and the amount of boil-off gas consumed by the gas processing device 70 is the amount of boil-off gas generated in the tank 20. Over. In this case, the propulsion engine 40 uses oil such as heavy oil as a supplemental fuel. In this control state, the control device 60 preferably sets the gas processing pressure set value to be lower than the liquefied gas pressure set value. 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 with an opening degree 0 (completely closed) to the contact 57c, and send a gas processing control signal with an opening degree 0 to the contact 71b.
Therefore, the liquefaction control valve 55 is completely closed by selecting the liquefaction sequence control signal with the opening degree 0 sent to the contact 57c by the selector 57b, and the gas treatment control valve 71a is opened to the contact point 71b by the selector 71c. 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 degree 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 degree of the gas processing control valve 71a according to the pressure of the boil-off gas in the tank 20. It is a gas processing control state.

  Thereafter, when the speed of the ship decreases to a certain level and the load of the propulsion engine 40 decreases, the sum of the boil-off gas consumption of the propulsion engine 40 and the boil-off gas consumption of the gas processing device 70 and the pressurizing mechanism 30 The amount of boil-off gas supplied (in the present embodiment, substantially corresponds to the amount of boil-off gas generated) matches. In this case, the consumption of supplementary fuel is reduced to zero with oil such as heavy oil.

  When the boil-off gas consumption of the propulsion engine 40 further decreases, the sum of the boil-off gas consumption of the propulsion engine 40 and the boil-off gas consumption of the gas processing device 70 is less than the boil-off gas supply amount by the pressurizing mechanism 30. Therefore, 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, but the opening of the gas processing control valve 71a is controlled to open in accordance with this increase, so the gas processing device 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 degree of the gas processing control valve 71a exceeds a set threshold value, the control device 60 generates a liquefaction sequence control signal that opens the liquefaction control valve 55 so that the boil-off gas flows into the liquefying device 50. That is, the control is performed so that the liquefaction control valve 55 is opened 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 boil-off gas of the pressurizing mechanism 30. To 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 with an opening of the gas processing control valve 71a of 0 is sent to the contact 71b, but the opening of the gas processing control valve 71a is a gas generated based on the pressure measured by the pressure gauge 57a. Control is performed according to the processing feedback control signal. On the other hand, a liquefaction sequence control signal with the opening degree of the liquefaction control valve 55 being 0 is sent to the contact 57c, and the opening degree of the liquefaction control valve 55 is 0 according to this liquefaction sequence control signal. Therefore, in this control state, the liquefaction pressure set value does not function for the liquefaction control valve 55.

4 (a) and 4 (b) show changes over time in the pressure measured by the pressure gauge 57a, the liquefaction pressure set value, and the gas processing pressure set value, and the liquefaction control valve 55 is opened in the liquefaction feedback control signal and liquefaction sequence control signal. It is a figure which shows the example of the time change of a degree. Time T1 represents the time when 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 gas processing pressure set value.
From such a control state, the control device 60 performs the following operations 1 and 2 at time T1. Furthermore, the control device 60 performs the following operation 3. By these operations, the control signal for controlling the opening degree 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 that the control device 60 sends 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 controller 60 to the contact 57c to the liquefaction feedback control signal based on the measured pressure of the pressure gauge 57a.

Operation 1:
The control device 60 changes the gas processing pressure set value to be large and the liquefaction pressure set value to be small, and sets the gas processing pressure set value to be larger than the liquefying 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 zero. The liquefaction sequence control signal is maintained and sent to the contact 57c.
In the state of this operation 1, the opening degree of the gas processing control valve 71a is set in accordance with the gas processing feedback control signal generated based on the difference between the measured pressure of the pressure gauge 57a and the gas processing pressure set value whose value has increased. Since the difference is increased, the opening degree of the gas processing control valve 71a is decreased. For this reason, as shown to Fig.4 (a), the measurement pressure of the pressure gauge 57a rises so that it may approach gas processing pressure setting value. As will be described later, at time T1, the liquefaction control valve 55 starts to open, but since the speed of the opening degree is small, a sufficient gas-liquid mixed fluid is not collected into the tank 20, so the measured pressure of the pressure gauge 57a is It rises to approach the gas processing pressure set value.

Operation 2:
At time T1, the control device 60 sends a liquefaction sequence control signal with a non-opening degree that opens the liquefaction control valve 55 slowly as a control signal to be sent to the contact 57c.
By this liquefaction sequence control signal, the liquefaction control valve 55 begins to open slowly via the selector 57b. In this case, the liquefaction sequence control signal is generated so that the opening speed of the liquefaction control valve 55 is initially small and gradually increases. Specifically, when the liquefaction control valve 55 is opened, the optimum recovered gas amount is the maximum boil-off gas flow rate that is most liquefied by the cooling of the boil-off gas by the heat exchanger 53 and the expansion of the boil-off gas by the expansion valve 54. The opening speed of the liquefaction control valve 55 is initially small so that a small flow rate flows through the liquefaction apparatus 50. Thereafter, the opening speed of the liquefaction control valve 55 is gradually increased so that the boil-off gas flowing in the liquefaction apparatus 50 approaches the optimum recovered 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 1 minute or more to reach a boil-off gas flow rate of 20% of the optimum recovered gas amount. It is preferable.

In this state, the pressure measured by the pressure gauge 57a rises until the amount of gas-liquid mixed fluid begins to be collected into the tank 20 until the amount of collection increases, but it 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 opening degree of the liquefaction control valve 55 is increased by the liquefaction sequence control signal sent to the contact 57c, and as shown in FIG. 4A, the pressure of the pressure gauge 57a starts to decrease. The opening degree of the liquefaction sequence control signal gradually increases as shown in FIG. 4B, and the opening degree of the liquefaction feedback control signal crosses the opening degree of the liquefaction feedback control signal. Less than degrees. Thereby, the selector 57b selects the liquefaction feedback control signal based on the measurement pressure of the pressure gauge 57a, and the opening degree of the liquefaction control valve 55 is controlled by the liquefaction feedback control signal. That is, the control signal for controlling the opening degree of the liquefaction control valve 55 is changed from a liquefaction sequence control signal sent to the contact 57c to a liquefaction feedback control signal based on the pressure measured by the pressure gauge 57a.

  On the other hand, since the measured pressure of the pressure gauge 57a is lower than the gas processing pressure set value, the opening of the gas processing feedback control signal becomes small. Thereby, the opening degree of the gas processing feedback control signal becomes lower than the opening degree 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 degree of the gas processing control valve 71a is sent from the gas processing feedback control signal based on the measured pressure of the pressure gauge 57a to the contact 71b. The gas processing sequence control signal is changed. Therefore, the opening degree of the gas processing control valve 71a can be adjusted by adjusting the opening degree 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 is performed on the gas processing feedback control signal of the control device 60. 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 integral value of the residual difference between the past gas processing feedback control signal and the measured pressure. Therefore, when the propulsion engine 40 fluctuates in load due to disturbance and the consumption of boil-off gas fluctuates and the pressure measured by the pressure gauge 57a changes suddenly, the PID control of the opening by the gas processing control valve 55 is stabilized. This is so that it can be performed.

  The liquefaction apparatus 50 stops the liquefaction of the boil-off gas and the recovery of the gas-liquid mixed fluid tank 20 by setting the liquefaction sequence control signal to a signal with an opening degree of 0 and setting the liquefaction pressure set value to the liquefaction of the boil-off gas and the gas-liquid. What is necessary is just to return to the state before collection | recovery of the tank 20 of mixed fluid, and to make a gas processing sequence control signal into the signal of the opening degree 0.

  As described above, the liquefaction apparatus 50 of the present embodiment includes the recovery pipe 56, and the gas-liquid mixed fluid of the liquefied gas liquefied by the liquefaction apparatus 50 and the boil-off gas that has not been liquefied through the recovery pipe 56 is converted into the liquefied gas in the tank 20. In the liquid phase. For this reason, as shown in FIG. 2, when the boil-off gas is joined to the boil-off gas flowing through the main pipe 31 through the joining pipe 57, the boil-off gas is caused by a change in the composition ratio of the boil-off gas caused by the joining of the boil-off gas. Difficulties in controlling the pressurization of the boil-off gas in the pressurizing mechanism 30 can be avoided. 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 either the gas processing control valve 71a or the liquefaction control valve 55 in accordance with the pressure of the boil-off gas in the tank 20, so that the pressure (pressure) of the boil-off gas in the tank 20 is controlled. (Measurement pressure of the total 57a) can control the pressure of the boil-off gas in the tank 20 within a predetermined range, and can prevent the tank 20 from being damaged by the increase in the pressure of the boil-off gas. ,preferable.

  The control device 60 controls the liquefaction control valve 55 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. Control to open is preferable from the viewpoint of suppressing 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 reduces 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 time, that is, increasing non-linearly. In addition, since a gas-liquid mixed fluid having a temperature higher than that of 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 increases abruptly 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 has a boil-off gas flow rate of 20% of the optimum recovered gas amount, which is the maximum boil-off gas flow rate at which the boil-off gas can be liquefied most by the liquefaction device 50 from the start of opening of the liquefaction control valve 55. The amount of boil-off gas flowing to the liquefaction device 50 is controlled by controlling the opening of the liquefaction control valve 55 so that the time until it reaches 1 minute or more is large in the liquefied gas in the tank 20. It is preferable from the point which suppresses that the heat | fever enters.

  When the control device 60 opens the liquefaction control valve 55, the control device 60 changes the pressure of the boil-off gas in the tank 20 from the gas processing control state in which the opening degree of the gas processing control valve 71a is controlled according to the pressure of the boil-off gas in the tank 20. Accordingly, 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, the pressure of the boil-off gas in the tank 20 in the two control states. Can be suppressed within a predetermined range.

  Further, as described above, the selector 71c selects a control signal having a larger opening instruction value among 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. Select and send to the gas processing control valve 7a, the selector 57b, as described above, of the opening indication value of 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 a separate body from the controller that generates the liquefaction feedback control signal and the controller that generates the gas processing feedback control signal.

  As described above, when the liquefaction control valve 55 is closed, the control device 60 has a gas processing pressure set value 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 gas processing pressure setting value and the liquefaction pressure setting value are adjusted so as to be larger than the setting value. 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 setting 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 setting value.

  Further, as described above, when the liquefaction control valve 55 is closed, the control device 60 sets the opening degree 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 so that the pressure of the boil-off gas in the tank 20 becomes the liquefaction pressure set value. Thereby, 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 having 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 in order to supply the boil-off gas vaporized 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 boil-off gas that has not been liquefied and is generated by liquefying a part of the boil-off gas that has been pressurized and sent out by the liquefaction device 50 is the liquid phase of the liquefied gas in the tank 20. Step back inside.

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

The fuel gas supply method further includes:
(3) flowing a part of the pressurized boil-off gas toward the gas processing device 70 that consumes part of the boil-off gas as fuel.
In this case, either the amount of boil-off gas flowing toward the gas processing device 70 or the amount of returning the gas-liquid mixed fluid to the liquid phase of the liquefied gas in the tank 20 is 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 tanked. It is preferable to perform the step of returning to the liquid phase of the liquefied gas in 20.

  Further, when the boil-off gas is caused to flow to the liquefying device 50 to start liquefaction, it is preferable to increase the amount of boil-off gas to be flowed to the liquefying device 50 continuously or stepwise over time.

  When liquefaction is started by flowing boil-off gas through the liquefier 50, the boil-off gas flow rate is 20% of the optimum recovered gas amount, which is the maximum boil-off gas flow rate at which the liquefaction device 50 can liquefy most boil-off gas. It is preferable to control the flow rate of the boil-off gas flowing through the liquefaction apparatus 50 so that the time until the flow rate is reached is 1 minute or longer.

  When the boil-off gas is supplied to the liquefying device 50 and liquefaction is started, the gas treatment 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 treatment pressure set value. Liquefaction is performed according to 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 setting value from the gas processing control state in which the amount of boil-off gas flowing to the apparatus 70 is controlled. 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 boil-off gas flowing to the apparatus 50 is controlled.

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

DESCRIPTION OF SYMBOLS 10 Fuel gas supply system 20 Tank 30 Pressurization mechanism 31 Main piping 32a-32e Gas compressor 33a, 33c, 33e Bypass pipe 34a, 34c, 34e, 55a, 57a Adjustment valve 35a-35e Suction snubber 36a-36e Discharge snubber 37a-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 Liquefaction device 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 58 Cooler 60 Control device 62 Engine control unit 70 Gas processing device 71a Gas processing control valve 156 Recovery piping

Claims (18)

A fuel gas supply system for supplying 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 as a fuel gas to the engine;
A liquefaction device for liquefying a part of the boil-off gas sent by being pressurized by the pressurization mechanism and returning it to the tank;
A control device for controlling the amount of boil-off gas flowing to the liquefying device;
With
The fuel is characterized in that the liquefier comprises a recovery pipe for returning the gas-liquid mixed fluid of the liquefied gas liquefied by the liquefier and the boil-off gas that has not been liquefied into the liquid phase of the liquefied gas in the tank. Gas supply system.   The fuel gas supply system according to claim 1, wherein the recovery pipe is provided with a cooling device that cools the gas-liquid mixed fluid. The fuel gas supply system further includes:
Gas processing control that is provided in a branch pipe connected to a gas processing apparatus that consumes a part of the boil-off gas pressurized by the pressurizing mechanism and controls the amount of boil-off gas that flows through the branch pipe toward the gas processing apparatus A valve,
A liquefaction control valve that controls the amount of boil-off gas flowing from the pressurizing mechanism to the liquefying device,
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 in accordance with the pressure of the boil-off gas in the tank. The fuel gas supply system according to claim 1 or 2.   The control device opens the liquefaction control valve when the total amount of voice-off gas consumed by the engine and boil-off gas consumed by the gas processing device is smaller than the amount of boil-off gas supplied by the pressurizing mechanism. The fuel gas supply system according to claim 3, wherein the fuel gas supply system is controlled as follows.   The fuel gas supply system according to claim 3 or 4, wherein the control device increases the speed of the opening of the liquefaction control valve continuously or stepwise with time.   The control device has a flow rate of 20% of the optimum recovered gas amount, which is the maximum boil-off gas flow rate at which the boil-off gas can be liquefied most by the liquefaction device from the start of opening of the liquefaction control valve. The fuel gas supply system according to claim 5, wherein an opening degree of the liquefaction control valve is controlled so that a time until it reaches 1 is 1 minute or more.   When the control device opens the liquefaction control valve, the control device changes the pressure of the boil-off gas in the tank from the gas processing control state in which the opening of the gas processing control valve is controlled according 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 to shift to a liquefaction control state in which the opening degree of the liquefaction control valve is controlled accordingly. Supply system. 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,
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 for instructing the opening 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;
A gas processing sequence control signal for instructing the opening of the gas processing 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 processing selector,
A liquefaction feedback control signal for instructing the opening of the liquefaction control valve so that the pressure of the boil-off gas in the tank becomes a set liquefaction pressure set value;
The liquefaction sequence control signal for instructing 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, and the selection for liquefaction To the vessel,
The gas processing selector selects a control signal having a larger indication value of the opening from the gas processing feedback control signal and the gas processing sequence control signal, and sends the control signal to the gas processing control valve.
The liquefying 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 selected control signal to the liquefaction control valve. The fuel gas supply system according to any one of claims.   The control device is configured such that when the liquefaction control valve is closed, the gas treatment pressure set value is lower than the liquefaction pressure set value, and when the liquefaction control valve is open, the gas treatment pressure set value is the liquefaction pressure. The fuel gas supply system according to claim 8, wherein the gas processing pressure setting value and the liquefaction pressure setting value are adjusted so as to be larger than a setting value.   The control device controls the liquefaction control by controlling an 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 when the liquefaction control valve is closed. 10. The fuel gas supply system according to claim 9, wherein when the valve is open, the opening degree 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. The fuel gas supply system according to any one of claims 1 to 10,
And a propulsion engine that is driven using fuel pressurized by the pressurizing mechanism. A fuel gas supply method for supplying fuel gas to an engine,
Pressurizing and sending out the boil-off gas vaporized from the liquefied gas by a pressurizing mechanism to supply the boil-off gas vaporized from the tank storing the liquefied gas as a fuel gas to the engine;
The gas-liquid mixed fluid containing the boil-off gas that has not been liquefied, which is generated by liquefying a part of the pressurized boil-off gas with a liquefier, is returned to the liquid phase of the liquefied gas in the tank. And a fuel gas supply method comprising the steps of:   The fuel gas supply method according to claim 12, further comprising a step of cooling the gas-liquid mixed fluid before returning it to the tank. The fuel gas supply method further includes a step of flowing toward a gas processing device that consumes a part of the pressurized boil-off gas as fuel,
Either the amount of boil-off gas that flows toward the gas processing device or the amount that returns the gas-liquid mixed fluid to the liquid phase of the liquefied gas in the tank depends on the pressure of the boil-off gas in the tank. The fuel gas supply method according to claim 12 or 13, wherein the pressure of the boil-off gas in the tank is controlled by controlling.   When the total amount of voice-off gas consumed by the engine and the amount of boil-off gas consumed by the gas processing device is smaller than the amount of boil-off supplied by the pressurizing mechanism, the gas-liquid mixed fluid is liquefied gas in the tank. The method for supplying 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 boil-off gas is caused to flow through the liquefaction device and liquefaction is started, the amount of boil-off gas to be fed to the liquefaction device is increased continuously or stepwise over time. Method.   When boil-off gas is supplied to the liquefier and liquefaction is started, the boil-off gas flow rate is 20% of the optimum recovered gas amount, which is the maximum boil-off gas flow rate at which the boil-off gas can be liquefied most by the liquefaction device. The fuel gas supply method according to claim 16, wherein the flow rate of the boil-off gas that flows to the liquefaction device is controlled so that the time until the flow rate is reached is 1 minute or longer. When the boil-off gas is supplied to the liquefaction device and liquefaction is started, the gas according to 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. According to 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 liquefaction pressure setting value from the gas processing control state for controlling the amount of boil-off gas flowing to the processing apparatus. 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 an amount of the boil-off gas flowing through the liquefaction device is controlled.

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