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 Art

[0002] A ship using boil-off gas (BOG) of liquefied gas as fuel is equipped with a gas supply system for supplying boil-off gas from a fuel tank storing liquefied gas to combustion treatment devices such as a main engine, a generator, a boiler, and a gas combustion unit (GCU). In such a system, boil-off gas is constantly generated due to heat input to the fuel tank during both navigation and docking, and excessive boil-off gas is likely to occur.

[0003] Excessive boil-off gas is also likely to occur when handling liquefied gas or boil-off gas. For example, boil-off gas is generated from the fuel tank, the bunkering hose, and the bunkering line due to heat input during the supply of liquefied gas from the outside to the fuel tank (bunkering). Also, during ship repairs, boil-off gas is generated by purging the boil-off gas remaining in the main engine or generator, or the liquefied gas and boil-off gas in the fuel tank with an inert gas. Furthermore, during system operation, boil-off gas may be discharged from a safety valve provided in a fuel tank or a pipe for transferring boil-off gas.

[0004] Excessive boil-off gas is treated, for example, by being burned by the above combustion treatment device (see Patent Document 1). Alternatively, excessive water-soluble boil-off gas can also be discarded at a concentration below the regulated value using a device (water-soluble gas treatment device) for dissolving it in seawater or fresh water to form an aqueous solution. <了

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, depending on the amount of boil-off gas generated, the processing capacity of the combustion treatment equipment or the water-soluble gas treatment equipment (hereinafter collectively referred to as "treatment equipment") may be insufficient, and the boil-off gas may not be able to be processed completely. In such cases, replacing the treatment equipment with one that has a higher processing capacity would increase the cost of the equipment and thus the cost of processing boil-off gas. Although boil-off gas can be used as fuel, it is undesirable from the perspective of efficient energy use to incur costs for treatment equipment simply for disposal through combustion, etc., without using it as fuel.

[0007] The present invention aims to provide a boil-off gas treatment system and a boil-off gas treatment method that can reduce the cost of treating excess boil-off gas, reduce the amount of boil-off gas that cannot be treated, and promote the effective utilization of boil-off gas. [Means for solving the problem]

[0008] This disclosure includes the following aspects: Appearance 1 A boil-off gas processing system for processing excess boil-off gas generated in a gas supply system that sends boil-off gas of liquefied gas to at least one supply destination, A container for storing at least a portion of the generated boil-off gas as a compressed gas or liquefied gas, At least one of the aforementioned supply destinations, comprising at least one processing apparatus for processing boil-off gas, A gas supply line for supplying boil-off gas to the processing apparatus, comprising: a gas supply line to which the container is connected and which has a first flow path section that serves as a flow path for the gas or liquefied gas; The boil-off gas processing system is characterized in that the processing apparatus processes boil-off gas that is removed from the container and guided by the gas supply line.

[0009] Appearance 2 The boil-off gas processing system according to embodiment 1, wherein the gas supply line is taken out of the container and includes a pressure reducing valve for reducing the pressure of the boil-off gas flowing through the gas supply line.

[0010] Appearance 3 The boil-off gas processing system according to embodiment 1 or 2, wherein the container is referred to as the first container, and further comprises at least one second container for storing at least a portion of the generated boil-off gas as a compressed gas or liquefied gas.

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

[0012] Appearance 5 A boil-off gas processing system according to embodiment 3 or 4, wherein the gas or liquefied gas stored in at least one of the containers is supplied to the processing device, while at least a portion of the generated boil-off gas is stored in at least one of the other containers.

[0013] Appearance 6 The boil-off gas processing system further comprises a fuel tank for storing liquefied gas that serves as a source of boil-off gas used at the recipient site. The gas supply line is connected to the fuel tank to take in boil-off gas generated in the fuel tank, The boil-off gas processing system according to any one of embodiments 1 to 5, wherein the gas supply line further has a second flow path to which the container is not connected, which is a flow path for boil-off gas from the fuel tank to the supply destination without passing through the first flow path.

[0014] Appearance 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. When the boil-off gas taken out from the container and flowing through the gas supply line cannot be supplied to the generator or the boiler, the boil-off gas treatment system according to Aspect 7 supplies the boil-off gas to the device that does not use boil-off gas as fuel.

[0015] Aspect 8 A method for treating surplus boil-off gas generated in a gas supply system that sends boil-off gas of liquefied gas to at least one supply destination, comprising: a storage step of storing at least a part 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 for treating boil-off gas; a treatment step of treating the boil-off gas taken out from the container and supplied to the treatment device using the treatment device. The method for treating boil-off gas is characterized by comprising the above steps.

Advantages of the Invention

[0016] According to the boil-off gas treatment system and the boil-off gas treatment method of the above aspect, it is possible to reduce the cost for treating surplus boil-off gas, reduce the boil-off gas that cannot be completely treated, and achieve effective utilization of boil-off gas.

Brief Description of the Drawings

[0017] [Figure 1] It is a diagram showing an example of a boil-off gas treatment system according to an embodiment. [Figure 2] It is a flowchart for explaining an example of boil-off gas treatment.

Modes for Carrying Out the Invention

[0018] Figure 1 shows an example of a boil-off gas treatment system according to one embodiment. The boil-off gas processing system 1 of this embodiment (hereinafter also referred to as "this system") is a system for processing excess boil-off gas (BOG) generated in a gas supply system (not shown).

[0019] A gas supply system is a system that delivers boil-off liquefied gas to at least one destination. In the following explanation, a fuel gas supply system installed on a ship that supplies boil-off gas as fuel gas to the internal combustion engines of the main engine or generator will be used as an example of a gas supply system. However, a gas supply system is not limited to this and may be a system installed on other means of transport such as a vehicle that supplies boil-off gas to the internal combustion engine of the means of transport, or a system that supplies boil-off gas to the internal combustion engine of an onshore facility such as a thermal power plant or storage base.

[0020] The vessel is preferably one that uses liquefied gas as propulsion fuel or power generation fuel (including vessels that use the transported liquefied gas as propulsion fuel or power generation fuel). Examples of the liquefied gases in question are liquefied natural gas (LNG), liquefied petroleum gas (LPG), liquefied hydrogen, and liquefied ammonia.

[0021] System 1 comprises containers 20 and 30, processing devices 41, 42, 43, and 44, and a gas supply line 10. Of these, at least the processing devices 41 to 44 and the portion of the gas supply line 10 excluding the first flow path section described later are common components with the gas supply system. The gas supply system shown in Figure 1 is an example that comprises a supply destination and the portion of the gas supply line 10 excluding the first flow path section, and the supply destination includes a main engine (not shown) and processing devices 41 to 44.

[0022] Containers 20 and 30 store at least a portion of the generated boil-off gas as compressed gas or liquefied gas. This allows for the 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 at the required pressure at the recipient.

[0023] Container 20 is a container for storing boil-off gas as liquefied gas. The liquefied gas is obtained by compressing the boil-off gas in a compressor 11a in the first flow path section 11 (described later) of the gas supply line 10, and then liquefying it in a re-liquefaction device 11b. Storing boil-off gas as liquefied gas in this way is preferable because it allows for the storage of a larger amount of boil-off gas when a large amount of boil-off gas is generated.

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

[0025] The processing units 41-44 are the recipients of the boil-off gas and are devices for processing the boil-off gas. Processing units 41-44 can process excess boil-off gas that is not stored in containers 20 and 30, as well as gas that is stored in containers 20 and 30 and later removed. The processing unit in the example shown in Figure 1 consists of generators 41a, 41b, and 41c, a boiler 42, a gas combustion unit (GCU) 43, and a water-soluble gas processing unit 44. The generators 41a-41c are equipped with, for example, diesel engines, dual-fuel engines, or gas turbines, and generate electricity required by various ship equipment using boil-off gas as fuel. To ensure redundancy, the power generation system is composed of three generators 41a-41c. The boiler 42 generates steam, which is mainly used as a heat source on board the ship, using boil-off gas as fuel. It is preferable to process boil-off gas using generators 41a to 41c and boiler 42, and in particular to process boil-off gas using generators 41a to 41c, from the viewpoint of effectively utilizing surplus boil-off gas as fuel. The water-soluble gas treatment device 44 is a device for dissolving water-soluble boil-off gas in seawater or fresh water to make an aqueous solution, and the boil-off gas can be processed by disposing of the aqueous solution at a concentration below the regulatory limit. 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 this system 1 may be equipped with only some of the generators 41a to 41c, boiler 42, gas combustion unit 43, and water-soluble gas treatment device 44 as treatment devices, and may also be further equipped with treatment devices other than treatment devices 41 to 44.

[0026] The gas supply line 10 is piping for guiding the boil-off gas generated in the gas supply system to the processing devices 41-44. In the example gas supply line 10 shown in Figure 1, there is a first flow path section 11 to which a container 20 is connected and which serves as a flow path for liquefied gas, and a first flow path section 12 to which a container 30 is connected and which serves as a flow path for compressed gas. In the gas supply line 10 shown in Figure 1, the liquid flow path is shown with a solid line, and the gas flow path is shown with a dashed line. The arrows shown along the gas supply line 10 indicate the direction in which the liquid or gas flows. By having such first flow path sections 11 and 12 in the gas supply line 10, the generated excess boil-off gas can be stored in containers 20 and 30, and the extracted compressed gas or liquefied gas can be supplied to the processing devices 41-44. In the example shown in Figure 1, the first flow path sections 11 and 12 are two of several branches that branch off from the upstream flow path section 14 of the gas supply line 10, and are installed in parallel with each other.

[0027] A compressor 11a and a reliquefaction device 11b are provided in the portion of the first flow channel 11 upstream of the container 20. The compressor 11a compresses the boil-off gas taken into the first flow channel 11 to a relatively low-pressure gas (e.g., 0.5 MPa to 1.0 MPa) to produce 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 produced by the compressor 11a to produce liquefied gas. A heater 11c is provided in the portion of the first flow channel 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 regulating valves 11d and 11e at the inlet and outlet ends.

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

[0030] The first flow path section 12 is provided with regulating valves 12d and 12e at its inlet and outlet ends.

[0031] The gas supply line 10 may have multiple first flow path sections 11 and 12, as shown in the example in Figure 1, or it may have only one or three or more. The multiple first flow path sections may be arranged in parallel or in series with respect to each other.

[0032] The gas supply line 10 in the example shown in Figure 1 has an upstream flow path section 14 and a downstream flow path section 15 on the upstream and downstream sides of the multiple branched flow path sections. The downstream flow path section 15 is branched into multiple sections to form flow paths for boil-off gas directed toward each of the processing devices 41 to 44. A control valve 14a is provided in the upstream flow path section 14, and control valves 15a, 15b, 15c, and 15d are provided in the downstream section. Control valve 15a is provided in the upstream section of the branched section that further branches toward boil-off gas directed toward each of the generators 41a to 41c. The control valves 11d, 11e, 12d, 12e, 14a, 15a to 15d are valves that adjust the pressure of the gas flowing in the gas supply line 10, and the flow path can be opened and closed by adjusting the degree of opening.

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

[0034] As mentioned above, in gas supply systems, boil-off gas is constantly generated due to the heat input to the fuel tank, and excess boil-off gas is likely to be produced. Excess boil-off gas is also likely to be produced when handling liquefied gas or boil-off gas. If it is possible to supply the generated boil-off gas to the main engine or generator, it can be effectively utilized as fuel. However, if the boil-off gas cannot be processed even then, burning it in a gas combustion unit or processing it using a water-soluble gas treatment device would result in the disposal of fuel obtained in exchange for payment. Also, even if steam is generated using a boiler while the ship is docked, there is little opportunity to use it as a heat source, making it essentially the same as disposal. Furthermore, if excess boil-off gas is generated while the main engine or generator is shut down while the ship is docked, it is not possible to burn and process the boil-off gas using a gas combustion unit in a location where it is undesirable to emit smoke or exhaust gases. If a large amount of boil-off gas is generated and the processing capacity of the treatment device is insufficient, it may not be possible to process the boil-off gas at all. In such cases, replacing the processing equipment with one that has higher processing capacity would increase the cost of the equipment and thus the cost of processing the boil-off gas.

[0035] In this system 1, excess boil-off gas generated in the gas supply system can be temporarily stored in containers 20 and 30, thus reducing the amount of boil-off gas that cannot be processed without replacing the processing equipment with one that has a higher processing capacity. In other words, with this system 1, it is possible to reduce the amount of boil-off gas that cannot be processed while keeping the cost of processing excess boil-off gas down, thereby promoting the effective use of boil-off gas.

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

[0037] According to one embodiment, the system 1 preferably comprises multiple containers, as shown in the example in Figure 1. By comprising multiple containers, more boil-off gas can be stored, and the amount of boil-off gas that cannot be processed can be significantly reduced. In the example shown in Figure 1, a pressure tank 21 and a cylinder cylinder 22 are connected to the first flow path section 11 as containers 20. A pressure tank 31 and a cylinder cylinder 32 are connected to the first flow path section 12 as containers 30. The pressure tanks 21 and 31 are containers installed, for example, on the deck of a ship, and are preferably containers capable of storing pressure at a higher pressure than the fuel tank 50 described later. Although not particularly limited, the volume of the pressure tanks 21 and 31 is, for example, 20 to 30 m³. 3The allowable pressure is, for example, 0.5 to 1.0 MPa. The cylinders 22 and 32 are containers that are detachably connected to the first flow paths 11 and 12. Although not particularly limited, the internal volume of the cylinders 22 and 32 is, for example, 15 to 20 m³. 3 The allowable pressure is, for example, 0.5 to 1.0 MPa. In the example shown in Figure 1, one cylinder cylinder 22 and 32 are provided in each of the first flow path sections 11 and 12, but two or more may be provided. In this specification, the pressure tank 21 and cylinder cylinder 22 are collectively referred to as container 20, and the pressure tank 31 and cylinder cylinder 32 are collectively referred to as container 30.

[0038] Preferably, at least one of each of the containers 20 and 30 is a cylinder cylinder 22 or 32, as shown in the example in Figure 1. This allows the cylinder cylinders 22 or 32 storing compressed or liquefied gas to be removed from the first flow path sections 11 or 12 and unloaded, or replaced with new, empty cylinder cylinders. By selling the unloaded cylinder cylinders 22 or 32 to others, for example, a portion of the fuel costs can be recovered. In addition, the cylinder cylinders 22 or 32 can be easily added in proportion to the amount of boil-off gas generated.

[0039] As shown in Figure 1, System 1 further includes a fuel tank 50 for storing liquefied gas that serves as a source of boil-off gas used at the destination of the gas supply system. The fuel tank 50 is a tank for storing liquefied gas that serves as a source of boil-off gas supplied mainly to the main engine of a ship. The main engine is, for example, a two-stroke cycle low-speed diesel engine. The liquefied gas in the fuel tank 50 is transported by a liquid transfer pump 51 towards the main engine through a supply line (not shown), where it is vaporized by a heater during transport, pressurized to high pressure by a compressor, and supplied to the main engine. According to one embodiment, the gas supply line 10 of 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 serves as a source of boil-off gas that fuels not only the main engine but also the generators 41a to 41c and the boiler 42.

[0040] According to one embodiment, the gas supply line 10 preferably has a second flow path section 13, as shown in the example in Figure 1. The second flow path section 13 is a flow path for boil-off gas that is not connected to containers 20 and 30 and travels from the fuel tank 50 to the supply destination without passing through the first flow paths 11 and 12. In the example shown in Figure 1, the second flow path section 13 is one of several flow paths that branch off 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. A control valve 13a is provided in the second flow path section 13. The control valve 13a is a valve that adjusts the pressure of the gas flowing in the gas supply line 10, and the flow path can be opened and closed by adjusting the degree of opening.

[0041] With such a gas supply line 10, the boil-off gas generated in the fuel tank 50 can be flowed through only one of the first flow channels 11, 12 and the second flow channel 13, or both, depending on the situation. For example, if the amount of boil-off gas generated is small, the boil-off gas can be flowed only through the second flow channel 13 and processed by the processing devices 41-44. Also, if the amount of boil-off gas generated is large and cannot be processed by the processing devices 41-44, the boil-off gas can be flowed through both the first flow channels 11, 12 and the second flow channel to store the boil-off gas in containers 20, 30 and to supply it to the processing devices 41-44. Alternatively, the boil-off gas can be flowed only through the first flow channels 11 and 12.

[0042] According to one embodiment, when the boil-off gas taken from containers 20 and 30 and flowing through the gas supply line 10 cannot be supplied to the generators 41a to 41c or the boiler 42, it is preferable that the system 1 supplies the boil-off gas to a device that does not use boil-off gas as fuel, namely a gas combustion unit 43 or a water-soluble gas treatment device 44. This allows the surplus boil-off gas to be used as fuel as much as possible. From the viewpoint of further effective utilization of the surplus boil-off gas, it is preferable that the boil-off gas taken from containers 20 and 30 and flowing through the gas supply line 10 cannot be supplied to the generators 41a to 41c, and instead supplies it to 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 this system 1, storage in containers 20 and 30 is performed when there is available capacity in containers 20 and 30, and when, for example, the pressure in the gas phase space inside 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. This is because if the pressure in the gas phase space inside 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 devices 41-44 for boil-off gas becomes insufficient, and the excess boil-off gas cannot be processed. For this reason, the fuel tank 50 is equipped with a pressure gauge (not shown) that detects the pressure in the gas phase space inside the tank. The second flow path section 13 is equipped with a flow meter (not shown) that measures 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). If the control device determines that the received pressure or flow rate has exceeded the threshold, it controls the control valve and switches the flow path of the boil-off gas in the gas supply line 10. In this process, the flow path can be switched so that boil-off gas does not flow through the second flow path section 13, allowing excess boil-off gas to be quickly stored in containers 20 and 30. On the other hand, by maintaining the state in which boil-off gas flows through the second flow path section 13, the storage and processing of boil-off gas can be carried out in parallel.

[0044] The presence or absence of empty capacity in containers 20 and 30 is determined, for example, by whether or not the internal pressure of containers 20 and 30 exceeds a predetermined threshold. For this reason, containers 20 and 30 are equipped with pressure gauges (not shown) to detect the internal pressure, and the signal indicating the pressure detected by the pressure gauges is transmitted to the control device to determine whether or not the threshold has been exceeded.

[0045] On the other hand, in this system 1, storage in containers 20 and 30 is stopped not only when the available capacity of containers 20 and 30 is depleted, but also, for example, when the pressure in the gas phase space within the fuel tank 50 or the flow rate of the boil-off gas flowing through the second flow path 13 falls below a predetermined threshold.

[0046] Furthermore, in this system 1, the decision of whether to store in only one of the containers 20 and 30 or in both, and furthermore, which of the two containers 20 and 30 to store in if only one is used, is made, for example, when the pressure in the gas phase space within the fuel tank 50 or the flow rate of the boil-off gas flowing through the second flow path 13 falls below a predetermined threshold.

[0047] In this system 1, the extraction of compressed gas or liquefied gas from containers 20 and 30 is preferably performed when the generators 41a to 41c or the boiler 42 are in operation, more preferably when the generators 41a to 41c are in operation. When extracting from containers 20 and 30, the flow path of the second flow path section 13 may be closed to stop the supply of boil-off gas from the second flow path section 13. This allows the compressed gas or liquefied gas stored in containers 20 and 30 to be supplied to the processing device with priority over the boil-off gas from the fuel tank 50 and consumed first. On the other hand, the extraction of compressed or liquefied gas from containers 20 and 30 may be performed when the generators 41a to 41c or the boiler 42 are not in operation. For example, if the pressure in the gas phase space within the fuel tank 50, or the flow rate of 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 activated and supplied to these treatment devices 43 and 44. This allows boil-off gas that has nowhere to go in the gas supply system to be processed without leaking to the outside.

[0048] Thus, with this system 1, the stored excess boil-off gas can be processed by the processing devices 41-44 at a different time than when it is generated. For example, excess boil-off gas stored while at anchor can be used or processed little by little over time using a processing device with insufficient processing capacity during the voyage after departure.

[0049] Preferably, the control device is configured to control the compressors 11a, 12a, the control valves 11d, 11e, 12d, 12e, 13a, 14a, 15a, 15b, 15c, 15d, and the pressure reducing valves 12b, 15e so that the operations described above are performed. Preferably, the system 1 further includes such a control device.

[0050] (Method for handling boil-off gas) Next, the boil-off gas treatment method of this embodiment will be described. Figure 2 shows a flowchart of the boil-off gas treatment method of this embodiment.

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

[0052] This processing method comprises a storage step S1, a supply step S2, and a processing step S3.

[0053] The storage step S1 is a step of storing at least a portion of the generated boil-off gas in a container as a compressed gas or liquefied gas. The container is preferably the same as the containers 20 and 30 of the boil-off gas processing 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 processing device which is at least one of the supply destinations. The processing device is preferably the same as the processing devices 41 to 44 of the boil-off gas processing system 1 described above.

[0055] Processing step S3 is the process of processing the boil-off gas, which has been removed from the container and supplied to the processing device, using the processing device.

[0056] According to this processing method, excess boil-off gas generated in the gas supply system can be temporarily stored in a container, thus reducing the amount of boil-off gas that cannot be processed without replacing the processing equipment with one that has a higher processing capacity. In other words, this system 1 makes it possible to reduce the amount of boil-off gas that cannot be processed while keeping the cost of processing excess boil-off gas down, thereby promoting the effective utilization of boil-off gas.

[0057] This processing method can be carried out, for example, using the boil-off gas processing system 1 described above. Alternatively, this processing method can be carried out using the boil-off gas processing system 1 described above, which has the following additional configurations. As described above, excess boil-off gas may be discharged from the fuel tank, gas supply line, or safety valves installed in the processing unit while the gas supply system is in operation. For example, the boil-off gas discharged from the safety valve can be stored in a container by guiding it through a vent line (not shown) that releases the gas that has passed through the safety valve to the atmosphere, to containers 20, 30 on the fuel tank or gas supply line 10 of system 1, or to a container connected to the vent line (a container other than containers 20, 30). In this case, the container functions as a buffer chamber.

[0058] This method is preferable, for example, when liquefied ammonia is used as the liquefied gas, compared to the method in which the ammonia gas discharged from the safety valve is guided to a water-soluble gas treatment device for treatment, in that it allows for the effective utilization of ammonia gas. If the boil-off gas treatment system 1 described above does not include a generator, boiler, and gas combustion unit as treatment devices, and only includes a water-soluble gas treatment device, the processing speed of the water-soluble gas treatment device may be insufficient depending on the amount of excess ammonia gas generated.

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

[0060] 1. Boil-off gas treatment system 10 Gas supply lines 11, 12 First channel section 11a, 12a compressors 11b Reliquefaction device 11c heater 11d, 11e, 12d, 12e, 13a, 14a, 15a, 15b, 15c, 15d Adjustment valve 12b, 15e Pressure Reducing Valve 13 Second channel section 14 Upstream flow path section 15 Downstream flow path section 20, 30 containers 21, 31 Pressure tanks 22, 32 cylinder cylinders 41, 42, 43, 44 Processing Units 41a, 41b, 41c Generators 42 Boiler 43 Gas combustion unit 44 Water-soluble gas treatment device 50 Fuel Tank 51. Liquid transfer pump

Claims

1. A boil-off gas processing system for processing excess boil-off gas generated in a gas supply system that sends boil-off gas of liquefied gas to at least one supply destination, A container for storing at least a portion of the generated boil-off gas as a compressed gas or liquefied gas, At least one of the aforementioned supply destinations, comprising at least one processing apparatus for processing boil-off gas, A gas supply line for supplying boil-off gas to the processing apparatus, comprising: a gas supply line to which the container is connected and which has a first flow path section that serves as a flow path for the gas or liquefied gas; The processing apparatus processes the boil-off gas that has been removed from the container and guided by the gas supply line. The gas supply line is taken out of the container and includes a pressure reducing valve that reduces the pressure of the boil-off gas flowing through the gas supply line. The boil-off gas, removed from the container and flowing through the gas supply line, is reduced to the pressure required by the processing device by the pressure reducing valve and supplied to the processing device. When the container is referred to as the first container, the system further comprises at least one second container for storing at least a portion of the generated boil-off gas as a compressed gas or liquefied gas. A boil-off gas treatment system characterized in that at least one of the containers is a cylinder cylinder detachably connected to the first flow path.

2. The boil-off gas processing system according to claim 1, wherein boil-off gas taken from the container and flowing through the gas supply line is supplied to the destination without compression.

3. The boil-off gas processing system according to claim 1, wherein the gas or liquefied gas stored in at least one of the containers is supplied to the processing device, and at least a portion of the generated boil-off gas is stored in at least one of the other containers.

4. The boil-off gas processing system further comprises a fuel tank for storing liquefied gas that serves as a source of boil-off gas used at the recipient site. The gas supply line is connected to the fuel tank to take in boil-off gas generated in the fuel tank, The boil-off gas processing system according to claim 1, wherein the gas supply line further has a second flow path to which the container is not connected, which is a flow path for boil-off gas from the fuel tank to the supply destination without passing through the first flow path.

5. The boil-off gas processing system comprises, as the processing device, a generator or boiler that uses boil-off gas as fuel, and a device that does not use boil-off gas as fuel. The boil-off gas processing system according to claim 4, wherein, when the boil-off gas taken from the container and flowing through the gas supply line cannot be supplied to the generator or the boiler, the boil-off gas is supplied to a device that does not use the boil-off gas as fuel.

6. A method for processing excess boil-off gas generated in a gas supply system that sends boil-off gas of liquefied gas to at least one supply destination, A storage step involves storing at least a portion of the generated boil-off gas as a compressed gas or liquefied gas in at least one of a plurality of containers. A supply step of supplying the gas or liquefied gas stored in the container to at least one processing device which is one of the supply destinations and processes boil-off gas, using the first flow path section of the gas supply line to which the container is connected as the flow path, The process includes a step of processing the boil-off gas, which has been removed from the container and supplied to the processing apparatus, using the processing apparatus, The boil-off gas extracted from the container is reduced to the pressure required by the processing device and supplied to the processing device. A method for processing boil-off gas, characterized in that at least one of the containers is a cylinder cylinder detachably connected to the first flow path.

Images