Boil-off gas treatment system and boil-off gas treatment method

Abstract

To reduce boil-off gas that cannot be treated and effectively use boil-off gas while reducing cost for treating surplus boil-off gas.SOLUTION: A boil-off gas treatment system in the embodiment is a boil-off gas treatment system for treating surplus boil-off gas generated in a gas supply system. The boil-off gas treatment system includes: a container that stores at least part of the generated boil-off gas as compressed air or liquefied gas; at least one treatment device that is at least one of supply destinations and treats the boil-off gas; and a gas supply line for supplying the boil-off gas to the treatment device, the gas supply line having the container connected thereto and including a first flow passage part serving as a flow passage of the gas or the liquefied gas. The treatment device treats the boil-off gas taken out from the container and guided by the gas supply line.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a boil-off gas treatment system for treating boil-off gas and a method for treating boil-off gas. [Background technology]

[0002] Ships that use boil-off gas (BOG) from liquefied gas as fuel are equipped with a gas supply system for supplying boil-off gas from a fuel tank that stores liquefied gas to combustion treatment devices such as main engines, generators, boilers, gas combustion units (GCUs), etc. In such a system, boil-off gas is constantly generated due to heat input to the fuel tanks, both while sailing and while anchored, and excess boil-off gas is likely to be generated.

[0003] Excess boil-off gas is also likely to be generated when handling liquefied gas or boil-off gas. For example, boil-off gas is generated from fuel tanks, bunkering hoses, and bunkering lines due to heat input when liquefied gas is supplied from the outside to a fuel tank (bunkering). In addition, boil-off gas is generated when boil-off gas remaining in the main engine or generator, or liquefied gas or boil-off gas in a fuel tank is purged with inert gas during ship repairs. Furthermore, boil-off gas may be discharged from safety valves installed in fuel tanks or piping for transporting boil-off gas during system operation.

[0004] The excess boil-off gas is treated, for example, by being combusted by the above-mentioned combustion treatment device (see Patent Document 1). Alternatively, the excess water-soluble boil-off gas can be disposed of at a concentration below the regulated value using a device for dissolving it in seawater or fresh water to prepare an aqueous solution (water-soluble gas treatment device). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2019-163804 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, depending on the amount of boil-off gas generated, the processing capacity of the combustion treatment device or the water-soluble gas treatment device (hereinafter, collectively referred to as the treatment device) may be insufficient, and the boil-off gas may not be completely treated. In that case, if the treatment device is replaced with one with a higher processing capacity, the cost of the device increases, and the cost of treating the boil-off gas also increases. Although boil-off gas can be used as fuel, it is not preferable from the viewpoint of effective energy utilization to incur costs for a treatment device just to dispose of the boil-off gas by burning it, without using it as fuel.

[0007] The present invention aims to provide a boil-off gas processing system and a boil-off gas processing method that can reduce the amount of boil-off gas that cannot be processed while suppressing the cost of processing surplus boil-off gas, and can effectively utilize the boil-off gas. [Means for solving the problem]

[0008] The present disclosure encompasses the following aspects. Aspect 1 A boil-off gas treatment system for treating excess boil-off gas generated in a gas supply system that sends boil-off gas of a liquefied gas to at least one supply destination, comprising: A container for storing at least a portion of the generated boil-off gas as a compressed gas or a liquefied gas; At least one processing device for processing the boil-off gas, which is at least one of the destinations; a gas supply line for supplying boil-off gas to the treatment device, the gas supply line having a first flow path portion to which the container is connected and which serves as a flow path for the gas or the liquefied gas; A boil-off gas treatment system, characterized in that the treatment device treats the boil-off gas taken out of the vessel and introduced through the gas supply line.

[0009] Aspect 2 2. The boil-off gas treatment system of claim 1, wherein the gas supply line comprises a pressure reducing valve for reducing the pressure of the boil-off gas taken from the vessel and flowing through the gas supply line.

[0010] Aspect 3 The boil-off gas treatment system according to aspect 1 or 2, further comprising at least one second vessel for storing at least a portion of the generated boil-off gas as compressed gas or liquefied gas, when the vessel is referred to as a first vessel.

[0011] Aspect 4 4. The boil-off gas treatment system according to claim 3, wherein at least one of the containers is a cylinder tank that is detachably connected to the first flow path portion.

[0012] Aspect 5 A boil-off gas treatment system according to aspect 3 or 4, wherein the gas or the liquefied gas stored in at least one of the vessels is supplied to the treatment device while at least a portion of the generated boil-off gas is stored in at least another of the vessels.

[0013] Aspect 6 The boil-off gas treatment system further includes a fuel tank for storing liquefied gas that is a supply source of the boil-off gas used at the supply destination, the gas supply line is connected to the fuel tank so as to take in boil-off gas generated in the fuel tank; The boil-off gas treatment system according to any one of claims 1 to 5, wherein the gas supply line further has a second flow path section to which the container is not connected, the second flow path section being a flow path for boil-off gas from the fuel tank to the destination without passing through the first flow path section.

[0014] Aspect 7 The boil-off gas treatment system according to aspect 7, comprising, as the treatment device, a generator or a boiler fueled by the boil-off gas, and a device that does not use the boil-off gas as fuel, and when the boil-off gas taken out of the container and flowing through the gas supply line cannot be supplied to the generator or the boiler, the boil-off gas treatment system supplies the boil-off gas to the device that does not use the boil-off gas as fuel.

[0015] Aspect 8 A method for treating excess boil-off gas generated in a gas supply system that sends boil-off gas of a liquefied gas to at least one supply destination, comprising: A storage step of storing at least a portion of the generated boil-off gas in a container as a compressed gas or a liquefied gas; A supply step of supplying the gas or liquefied gas stored in the container to at least one of the supply destinations, which is at least one treatment device that treats boil-off gas; and a processing step of processing the boil-off gas taken out of the vessel and supplied to the processing device using the processing device. Effect of the Invention

[0016] According to the boil-off gas treatment system and the boil-off gas treatment method of the above aspects, it is possible to reduce the amount of boil-off gas that cannot be treated while suppressing the cost of treating excess boil-off gas, thereby enabling effective use of the boil-off gas. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 illustrates an example of a boil-off gas treatment system according to an embodiment. [Diagram 2] 1 is a flowchart illustrating an example of a boil-off gas treatment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] FIG. 1 shows an example of a boil-off gas treatment system according to one embodiment. A boil-off gas treatment system (hereinafter, also referred to as this system) 1 of this embodiment is a system that treats excess boil-off gas (BOG) generated in a gas supply system (not shown).

[0019] The gas supply system is a system that sends boil-off gas of liquefied gas to at least one supply destination. In the following description, a fuel gas supply system that is mounted on a ship and supplies boil-off gas as fuel gas to an internal combustion engine of a main engine or a generator will be described as an example of the gas supply system, but the gas supply system is not limited to this and may be a system that is mounted on other means of transportation such as a vehicle and supplies boil-off gas to an internal combustion engine of the means of transportation, or a system that supplies boil-off gas to an internal combustion engine in a land facility such as a thermal power plant or a storage base.

[0020] The ship is preferably a ship that uses liquefied gas as a propulsion fuel or a power generation fuel (including a ship that uses the liquefied gas it transports as a propulsion fuel or a power generation fuel). Examples of the liquefied gas include liquefied natural gas (LNG), liquefied petroleum gas (LPG), liquefied hydrogen, and liquefied ammonia.

[0021] The system 1 includes containers 20 and 30, processing devices 41, 42, 43 and 44, and a gas supply line 10. The system 1 includes at least the processing devices 41-44 and a portion of the gas supply line 10 excluding a first flow path portion, which will be described later, as components common to the gas supply system. The gas supply system of the example shown in FIG. 1 includes a supply destination and a portion of the gas supply line 10 excluding the first flow path portion, and the supply destination includes a main engine (not shown) and processing devices 41-44.

[0022] The vessels 20 and 30 store at least a part of the generated boil-off gas as compressed gas (compressed gas) or liquefied gas. This allows for temporary storage of excess boil-off gas. By storing the boil-off gas as compressed gas or liquefied gas, a large amount of boil-off gas can be stored and supplied after appropriately reducing the pressure to the pressure required by the supply destination.

[0023] The container 20 is a container for storing the boil-off gas as a liquefied gas. The liquefied gas is obtained by compressing the boil-off gas by a compressor 11a in a first flow path section 11 (described later) of the gas supply line 10 and further liquefying the boil-off gas by a reliquefaction device 11b. Storing the boil-off gas as a liquefied gas in this manner is preferable in that a larger amount of boil-off gas can be stored when a large amount of boil-off gas is generated.

[0024] The container 30 is a container for storing the boil-off gas as compressed gas. The compressed gas is obtained by compressing the boil-off gas by a compressor 12a in a first flow path section 12 (described later) of the gas supply line 10. Storing the boil-off gas as compressed gas in this manner is preferable in that a re-liquefaction device is not required and the cost for storing the boil-off gas can be reduced. The pressure of the compressed gas in the container 30 is preferably 0.5 MPa or more, more preferably 1 MPa or more, so that the pressure does not need to be increased when the compressed gas is supplied to the generators 41a to 41c described later. On the other hand, the pressure of the compressed gas in the container 30 is preferably 1 MPa or more, more preferably 1.5 MPa or more, so that a larger amount of boil-off gas can be stored.

[0025] The treatment devices 41 to 44 are devices to which the boil-off gas is supplied and treat the boil-off gas. The treatment devices 41 to 44 can treat the excess boil-off gas that is not stored in the containers 20 and 30 and the excess boil-off gas that is stored in the containers 20 and 30 and later removed. The treatment devices in the example shown in FIG. 1 are generators 41a, 41b, and 41c, a boiler 42, a gas combustion unit (GCU) 43, and a water-soluble gas treatment device 44. The generators 41a to 41c are equipped with, for example, a diesel engine, a dual fuel engine, or a gas turbine, and generate electricity required by various devices of the ship using the boil-off gas as fuel. To ensure redundancy, a power generation system is configured with three generators 41a to 41c. The boiler 42 uses the boil-off gas as fuel to generate steam that is used as the main heat source on the ship. Treating boil-off gas using the generators 41a-41c and the boiler 42, particularly using the generators 41a-41c, is preferable from the viewpoint of effectively using surplus boil-off gas as fuel. The water-soluble gas treatment device 44 is a device for dissolving the water-soluble boil-off gas in seawater or fresh water to prepare an aqueous solution, and the boil-off gas can be treated by reducing the concentration of the aqueous solution to a regulated value or less and disposing of it. The water-soluble gas treatment device 44 is preferably provided as a treatment device when liquefied ammonia is used as the liquefied gas. Note that the present system 1 may include only some of the generators 41a-41c, the boiler 42, the gas combustion unit 43, and the water-soluble gas treatment device 44 as treatment devices, or may further include treatment devices other than the treatment devices 41-44.

[0026] The gas supply line 10 is a pipe for guiding boil-off gas generated in the gas supply system to the processing devices 41-44. The gas supply line 10 in the example shown in FIG. 1 has a first flow path section 11 to which the container 20 is connected and which serves as a flow path for liquefied gas, and a first flow path section 12 to which the container 30 is connected and which serves as a flow path for compressed gas. In the gas supply line 10 shown in FIG. 1, a portion which serves as a flow path for liquid is indicated by a solid line, and a portion which serves as a flow path for gas is indicated by a dashed line. In addition, the arrows shown along the gas supply line 10 indicate the direction in which the liquid or gas flows. Since the gas supply line 10 has such first flow path sections 11 and 12, the generated excess boil-off gas can be stored in the containers 20 and 30, and the extracted compressed gas or liquefied gas can be supplied toward the processing devices 41-44. In the example shown in FIG. 1, the first flow path sections 11 and 12 are two of a plurality of branches from the upstream flow path section 14 of the gas supply line 10, and are provided in parallel with each other.

[0027] A compressor 11a and a reliquefaction device 11b are provided in a portion of the first flow path section 11 upstream of the container 20. The compressor 11a compresses the boil-off gas taken into the first flow path section 11 into a gas of relatively low pressure (for example, 0.5 MPa to 1.0 MPa) to generate compressed gas. The reliquefaction device 11b has a heat exchanger (not shown) and uses a refrigerant such as liquid nitrogen as a cooling source to cool and condense the compressed gas of the boil-off gas generated by the compressor 11a to generate liquefied gas. A heater 11c is provided in a portion of the first flow path section 11 downstream of the container 20. The heater 11c heats the liquefied gas taken out of the container 20 to vaporize the liquefied gas.

[0028] The first flow path section 11 is further provided with adjustment valves 11d, 11e at the inlet and outlet sides.

[0029] A compressor 12a is provided in a portion of the first flow path section 12 upstream of the container 30. The compressor 12a compresses the boil-off gas taken into the first flow path section 11 into a gas with a relatively low pressure (for example, 0.5 MPa to 1.0 MPa) to generate a compressed gas.

[0030] The first flow path section 12 is provided with adjustment valves 12d, 12e at the inlet and outlet sides.

[0031] The gas supply line 10 may have a plurality of first flow path sections 11, 12, or may have only one, or may have three or more, as in the example shown in Fig. 1. The plurality of first flow path sections are provided in parallel or in series with each other.

[0032] The gas supply line 10 of the example shown in FIG. 1 has an upstream flow passage section 14 and a downstream flow passage section 15 on the upstream and downstream sides of the flow passage section branched into a plurality of sections. The downstream flow passage section 15 branches into a plurality of sections so as to form flow passages for the boil-off gas heading toward each of the processing devices 41 to 44. The upstream flow passage section 14 is provided with an adjustment valve 14a, and adjustment valves 15a, 15b, 15c, and 15d are provided in the downstream section. The adjustment valve 15a is provided in the upstream section of the further branched branch so that the boil-off gas heads toward each of the generators 41a to 41c. The above-mentioned adjustment valves 11d, 11e, 12d, 12e, 14a, 15a to 15d are valves for adjusting the pressure of the gas flowing in the gas supply line 10, and the flow passages can be opened and closed by adjusting the opening degree.

[0033] In order to stabilize the flow rate of the boil-off gas flowing toward the treatment devices 41 to 44, the gas supply line 10 may further be provided with one or more buffer tanks (not shown) at one or more locations.

[0034] As described above, in the gas supply system, boil-off gas is constantly generated due to heat input to the fuel tank, and excess boil-off gas is likely to be generated. In addition, excess boil-off gas is also likely to be generated when liquefied gas or boil-off gas is handled. In that case, if the generated boil-off gas can be supplied to the main engine or the generator, the boil-off gas can be effectively used as fuel. However, if the boil-off gas cannot be completely processed, the fuel obtained in exchange for a price will be discarded if it is burned in a gas combustion unit or processed using a water-soluble gas processing device. In addition, even if steam is generated using a boiler while the ship is anchored, there is almost no opportunity for it to be used as a heat source, and it is no different from discarding it. Furthermore, if excess boil-off gas is generated while the main engine or the generator is not operating during anchorage, it is not possible to burn and process the boil-off gas using a gas combustion unit in a place where it is not desirable to emit smoke or exhaust gas. If a large amount of boil-off gas is generated and the processing capacity of the processing device is insufficient, the boil-off gas cannot be processed in the first place. In such a case, if the treatment device is replaced with one having a higher treatment capacity, the cost of the device will increase, and the cost of treating the boil-off gas will also increase.

[0035] In the present system 1, the excess boil-off gas generated in the gas supply system can be temporarily stored in the containers 20 and 30, so that the amount of boil-off gas that cannot be treated can be reduced without replacing the treatment device with one with a higher treatment capacity. That is, according to the present system 1, the amount of boil-off gas that cannot be treated can be reduced while suppressing the cost for treating the excess boil-off gas, and the boil-off gas can be effectively utilized.

[0036] According to one embodiment, the first flow passage section 11, 12 preferably includes pressure reducing valves 12b, 15e for reducing the pressure of the compressed gas or vaporized liquefied gas flowing through the first flow passage section 11, 12. The pressure reducing valve 15e is provided in the downstream flow passage section 15 of the gas supply line 10 at a portion upstream of the branching portion. The pressure reducing valve 12b is provided in the first flow passage section 12 at a portion downstream of the container 30. The surplus boil-off gas is stored in the containers 20, 30 as compressed gas or liquefied gas, and can be appropriately reduced in pressure according to the pressure required by each of the processing devices 41-44 and supplied to the processing devices 41-44. On the other hand, the compressed gas taken out from the container 30 may be supplied to the generators 41a-41c without being reduced in pressure by the pressure reducing valve 12b. The compressed gas taken out from the container 20 and vaporized may be supplied to the generators 41a-41c without being reduced in pressure by the pressure reducing valve 15e. Since the generators 41a to 41c are required to supply the boil-off gas at a higher pressure than the other treatment devices 42 to 44, it is preferable that the pressure is not reduced in this manner depending on the pressure of the compressed gas. Note that the gas supply line 10 may be provided with another pressure reducing valve in addition to the pressure reducing valves 12b and 15e, and may be provided, for example, in a portion of the first flow path section 11 downstream of the container 20.

[0037] According to one embodiment, the present system 1 preferably includes a plurality of containers as in the example shown in FIG. 1. By including a plurality of containers, a larger amount of boil-off gas can be stored, and the amount of boil-off gas that cannot be treated can be significantly reduced. In the example shown in FIG. 1, a pressure tank 21 and a cylinder cylinder 22 are connected to the first flow path section 11 as the container 20. A pressure tank 31 and a cylinder cylinder 32 are connected to the first flow path section 12 as the container 30. The pressure tanks 21 and 31 are containers that are installed on the deck of a ship, for example, and are preferably containers that can accumulate pressure at a higher pressure than a fuel tank 50, which will be described later. Although not particularly limited, the volume of the pressure tanks 21 and 31 is, for example, 20 to 30 m 3The allowable pressure is, for example, 0.5 to 1.0 MPa. The cylinder cylinders 22 and 32 are containers that are detachably connected to the first flow passage portions 11 and 12. Although not particularly limited, the internal volume of the cylinder cylinders 22 and 32 is, for example, 15 to 20 m 3 and the allowable pressure is, for example, 0.5 to 1.0 MPa. In the example shown in Fig. 1, one cylinder cylinder 22, 32 is provided in each of the first flow path portions 11, 12, but two or more cylinder cylinders may be provided. In this specification, the pressure tank 21 and the cylinder cylinder 22 are collectively referred to as the container 20, and the pressure tank 31 and the cylinder cylinder 32 are collectively referred to as the container 30, as appropriate.

[0038] At least one of the containers 20, 30 is preferably a cylinder cylinder 22, 32, as in the example shown in Fig. 1. This allows the cylinder cylinder 22, 32 storing compressed gas or liquefied gas to be removed from the first flow path section 11, 12 and landed, or replaced with a new empty cylinder cylinder. By selling the landed cylinder cylinder 22, 32 to a third party, for example, it is possible to recover part of the fuel cost. In addition, the cylinder cylinder 22, 32 can be easily added depending on the amount of boil-off gas generated.

[0039] As shown in FIG. 1, the system 1 further includes a fuel tank 50 for storing liquefied gas that is a supply source of boil-off gas used at the supply destination of the gas supply system. The fuel tank 50 is a tank for storing liquefied gas that is a supply source of boil-off gas supplied mainly to the main engine of the ship. The main engine is, for example, a low-speed diesel engine of a two-stroke cycle. The liquefied gas in the fuel tank 50 is transferred by a liquid transfer pump 51 through a supply line (not shown) toward the main engine, and is vaporized by a heater during the transfer, compressed to a high pressure by a compressor, and supplied to the main engine. According to one embodiment, the gas supply line 10 of the system 1 is connected to the fuel tank 50 so as to take in the boil-off gas generated in the fuel tank 50. Therefore, the liquefied gas stored in the fuel tank 50 is a supply source of boil-off gas that is fuel not only for the main engine but also for the generators 41a to 41c and the boiler 42.

[0040] According to an embodiment, the gas supply line 10 preferably has a second flow path section 13 as in the example shown in FIG. 1. The second flow path section 13 is a flow path of boil-off gas that is not connected to the containers 20 and 30 and that travels from the fuel tank 50 to the supply destination without passing through the first flow path sections 11 and 12. In the example shown in FIG. 1, the second flow path section 13 is one of a plurality of flow paths branched from the upstream flow path section 14 of the gas supply line 10, and extends between the upstream flow path section 14 and the downstream flow path section 15. The second flow path section 13 is provided with an adjustment valve 13a. The adjustment valve 13a is a valve that adjusts the pressure of the gas flowing in the gas supply line 10, and can open and close the flow path by adjusting the opening degree.

[0041] According to such a gas supply line 10, the boil-off gas generated in the fuel tank 50 can be made to flow to only one or both of the first flow passage parts 11, 12 and the second flow passage part 13 depending on the situation. For example, when the amount of boil-off gas generated is small, the boil-off gas can be made to flow only to the second flow passage part 13 and treated by the treatment devices 41-44. When the amount of boil-off gas generated is large and cannot be treated by the treatment devices 41-44, the boil-off gas can be made to flow to both the first flow passage parts 11, 12 and the second flow passage part, so that the boil-off gas can be stored in the containers 20, 30 and supplied to the treatment devices 41-44. Alternatively, the boil-off gas can be made to flow only to the first flow passage parts 11, 12.

[0042] According to one embodiment, in the present system 1, when the boil-off gas taken out from the containers 20, 30 and flowing through the gas supply line 10 cannot be supplied to the generators 41a-41c or the boiler 42, it is preferable to supply the boil-off gas to a device that does not use the boil-off gas as fuel, that is, the gas combustion unit 43 or the water-soluble gas treatment device 44. This allows the excess boil-off gas to be used as fuel as much as possible. From the viewpoint of further effective use of the excess boil-off gas, when the boil-off gas taken out from the containers 20, 30 and flowing through the gas supply line 10 cannot be supplied to the generators 41a-41c, it is preferable to supply the boiler 42, the gas combustion unit 43 or the water-soluble gas treatment device 44.

[0043] The system 1 described above is preferably further configured as follows. In the present system 1, storage in the containers 20, 30 is performed when the containers 20, 30 have free capacity, for example, when the pressure of the gas phase space in the fuel tank 50 or the flow rate of the boil-off gas flowing through the second flow path section 13 described later exceeds a predetermined threshold. If the pressure of the gas phase space in the fuel tank 50 or the flow rate of the boil-off gas flowing through the second flow path section 13 exceeds the threshold, the processing capacity of the processing device 41-44 for the boil-off gas becomes insufficient, and the excess boil-off gas cannot be processed. For this reason, the fuel tank 50 is provided with a pressure gauge (not shown) for detecting the pressure of the gas phase space in the tank. The second flow path section 13 is provided with a flow meter (not shown) for measuring the flow rate of the boil-off gas. Signals indicating the pressure detected by the pressure gauge and the flow rate measured by the flow meter are transmitted to a control device (not shown). When it is determined that the received pressure or flow rate exceeds the threshold, the control device controls the regulating valve to switch the flow path of the boil-off gas in the gas supply line 10. At that time, the flow path is switched so that the boil-off gas does not flow through the second flow path section 13, so that the excess boil-off gas can be quickly stored in the containers 20 and 30. On the other hand, by maintaining a state in which the boil-off gas flows through the second flow path section 13, the boil-off gas can be stored and treated in parallel.

[0044] The presence or absence of free space in the containers 20, 30 is determined, for example, by whether the internal pressure of the containers 20, 30 exceeds a predetermined threshold value. For this reason, the containers 20, 30 are provided with a pressure gauge (not shown) for detecting the internal pressure, and a signal indicating the pressure detected by the pressure gauge is transmitted to a control device, which determines whether the threshold value has been exceeded.

[0045] On the other hand, in the present system 1, storage in the containers 20, 30 is stopped not only when the containers 20, 30 have no free capacity, but also when, for example, the pressure of the gas phase space in the fuel tank 50 or the flow rate of the boil-off gas flowing through the second flow path section 13 falls below a predetermined threshold value.

[0046] In addition, in the present system 1, a decision as to whether to store the fuel in only one of the containers 20, 30 or in both, and further, if storing the fuel in only one of the containers 20, 30, in which container to store the fuel, is made, for example, when the pressure of the gas phase space in the fuel tank 50 or the flow rate of the boil-off gas flowing through the second flow path section 13 falls below a predetermined threshold value.

[0047] In the present system 1, the compressed gas or liquefied gas is preferably taken out from the containers 20, 30 when the generators 41a-41c or the boiler 42 are operating, more preferably when the generators 41a-41c are operating. When taking out the gas from the containers 20, 30, the flow path of the second flow path section 13 may be closed to stop the supply of the boil-off gas from the second flow path section 13. This allows the compressed gas or liquefied gas stored in the containers 20, 30 to be supplied to the treatment device in preference to the boil-off gas from the fuel tank 50, and to be consumed first. On the other hand, the compressed gas or liquefied gas may be taken out from the containers 20, 30 when the generators 41a-41c or the boiler 42 are not operating. For example, when the pressure of the gas phase space in the fuel tank 50 or the flow rate of the boil-off gas flowing through the second flow path section 13 exceeds a predetermined threshold, the gas combustion unit 43 or the water-soluble gas treatment device 44 can be started and the gas can be supplied to these treatment devices 43, 44. This allows the boil-off gas that has lost its place in the gas supply system to be treated without leaking to the outside.

[0048] In this way, according to the present system 1, the stored excess boil-off gas can be processed by the treatment devices 41 to 44 at a timing different from the timing at which it was generated. For example, the excess boil-off gas stored while at anchor can be used as fuel or processed little by little over time, such as during a voyage after departure from port, using a treatment device with a lower processing capacity.

[0049] In order to perform the above-described operations, the control device is preferably configured to control the compressors 11a and 12a, the regulating valves 11d, 11e, 12d, 12e, 13a, 14a, 15a, 15b, 15c, and 15d, and the pressure reducing valves 12b and 15e. The present system 1 preferably further includes such a control device.

[0050] (Method of treating boil-off gas) Next, the boil-off gas treatment method of this embodiment will be described. Fig. 2 shows a flow chart of the boil-off gas treatment method of this embodiment.

[0051] The boil-off gas treatment method of this embodiment (hereinafter also referred to as the present treatment method) is a boil-off gas treatment method for treating excess boil-off gas generated in a gas supply system that sends the boil-off gas of a liquefied gas to at least one supply destination. The gas supply system, the liquefied gas, and the supply destination are preferably the same as the gas supply system, the liquefied gas, and the supply destination described for the boil-off gas treatment system 1.

[0052] This processing method includes a storage step S1, a supplying step S2, and a processing step S3.

[0053] The storage step S1 is a step of storing at least a part of the generated boil-off gas as compressed gas or liquefied gas in a container. The container is preferably similar to the containers 20 and 30 of the boil-off gas treatment system 1 described above.

[0054] The supply step S2 is a step of supplying the gas or liquefied gas stored in the container to at least one treatment device, which is at least one of the supply destinations. The treatment device is preferably the same as the treatment devices 41 to 44 of the boil-off gas treatment system 1 described above.

[0055] The treatment step S3 is a step of treating the boil-off gas taken out of the vessel and supplied to the treatment device using the treatment device.

[0056] According to this treatment method, the excess boil-off gas generated in the gas supply system can be temporarily stored in a container, so that the amount of boil-off gas that cannot be treated can be reduced without replacing the treatment device with one with a higher treatment capacity. In other words, according to this system 1, the amount of boil-off gas that cannot be treated can be reduced while suppressing the cost for treating the excess boil-off gas, and the boil-off gas can be effectively utilized.

[0057] This treatment method can be carried out, for example, by using the above-mentioned boil-off gas treatment system 1. On the other hand, this treatment method can be carried out by using the above-mentioned boil-off gas treatment system 1 having the following additional configuration. As described above, excess boil-off gas may be discharged from a safety valve installed in a fuel tank, a gas supply line, or a processing device during operation of the gas supply system. For example, the boil-off gas discharged from the safety valve can be stored in a container by leading the boil-off gas discharged from a safety valve to a container 20 or 30 on the fuel tank or gas supply line 10 of the system 1 or a container (a container different from the containers 20 and 30) connected to the vent line (not shown) through a vent line for releasing the gas that has passed through the safety valve to the atmosphere. In this case, the container functions as a buffer chamber.

[0058] Such a method is preferable in that it can effectively utilize ammonia gas, compared with a case where ammonia gas discharged from a safety valve is led to a water-soluble gas treatment device for treatment when liquefied ammonia is used as the liquefied gas, for example. If the boil-off gas treatment system 1 does not include a generator, a boiler, and a gas combustion unit as a treatment device, and includes only a water-soluble gas treatment device, the treatment speed of the water-soluble gas treatment device is likely to be insufficient depending on the amount of surplus ammonia gas generated.

[0059] The boil-off gas treatment system and the boil-off gas treatment method of the present invention have been described above. However, the present invention is not limited to the above-described embodiment, and various improvements and modifications may be made without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0060] 1. Boil-off gas treatment system 10 Gas supply line 11, 12 First flow path section 11a, 12a compressor 11b Reliquefaction device 11c heater 11d, 11e, 12d, 12e, 13a, 14a, 15a, 15b, 15c, 15d Regulating valve 12b, 15e Pressure reducing valve 13 Second flow path section 14 Upstream flow path section 15 Downstream flow path section 20, 30 containers 21, 31 Pressure tank 22, 32 cylinder cylinder 41, 42, 43, 44 Processing equipment 41a, 41b, 41c Generators 42 Boiler 43 Gas Combustion Unit 44 Water-soluble gas treatment equipment 50 Fuel Tank 51 Liquid delivery pump

Claims

1. A boil-off gas treatment system for treating excess boil-off gas generated in a gas supply system that sends boil-off gas of a liquefied gas to at least one supply destination, comprising: A container for storing at least a portion of the generated boil-off gas as a compressed gas or a liquefied gas; At least one treatment device for treating the boil-off gas, which is at least one of the destinations; a gas supply line for supplying boil-off gas to the treatment device, the gas supply line having a first flow path portion to which the container is connected and which serves as a flow path for the gas or the liquefied gas; A boil-off gas treatment system, characterized in that the treatment device treats the boil-off gas taken out of the vessel and introduced through the gas supply line.

2. 2. The boil-off gas treatment system of claim 1, wherein the gas supply line is provided with a pressure reducing valve for reducing the pressure of the boil-off gas taken from the vessel and flowing through the gas supply line.

3. 2. The boil-off gas treatment system of claim 1, further comprising at least one second vessel for storing at least a portion of the generated boil-off gas as compressed gas or liquefied gas, when the vessel is referred to as a first vessel.

4. The boil-off gas treatment system according to claim 3 , wherein at least one of the containers is a cylinder bomb that is detachably connected to the first flow path portion.

5. 5. The boil-off gas treatment system according to claim 3 or 4, wherein the gas or the liquefied gas stored in at least one of the containers is supplied to the treatment device, while at least a portion of the generated boil-off gas is stored in at least another one of the containers.

6. The boil-off gas treatment system further includes a fuel tank for storing liquefied gas that is a supply source of the boil-off gas used at the supply destination, the gas supply line is connected to the fuel tank so as to take in boil-off gas generated in the fuel tank; 5. The boil-off gas treatment system according to claim 1, further comprising a second flow path section to which the container is not connected, the second flow path section being a flow path for boil-off gas from the fuel tank to the destination without passing through the first flow path section.

7. The boil-off gas treatment system includes, as the treatment device, a generator or a boiler that uses boil-off gas as fuel, and a device that does not use boil-off gas as fuel, The boil-off gas treatment system according to claim 6, wherein the boil-off gas taken out of the container and flowing through the gas supply line is supplied to an apparatus that does not use the boil-off gas as fuel when the boil-off gas cannot be supplied to the generator or the boiler.

8. A method for treating excess boil-off gas generated in a gas supply system that sends boil-off gas of a liquefied gas to at least one supply destination, comprising: A storage step of storing at least a portion of the generated boil-off gas in a container as a compressed gas or a liquefied gas; A supply step of supplying the gas or liquefied gas stored in the container to at least one of the supply destinations, the supply destination being at least one treatment device that treats boil-off gas; a processing step of processing the boil-off gas taken out of the vessel and supplied to the processing device using the processing device.

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