Gas fuel supply system

Abstract

To provide a fuel supply system capable of preventing backfire or the like of flame of combustible gas ignited in the atmosphere outside a vent mast into the vent mast while suppressing a use amount of inert gas.SOLUTION: A gas fuel supply system 1 according to an embodiment includes a tank 2 that stores a liquified gas, and a gas fuel supply line 3 that leads out the liquified gas from the tank 2 and guides a vaporized gas obtained by vaporizing the liquified gas as a gas fuel to a gas consumption machine 4A. Further, the gas fuel supply system 1 includes the discharge line 6 that guides the flammable gas, which is at least one of the boil-off gas generated in the tank 2 and the gas fuel remaining in the gas fuel supply line 3, to the vent mast 11,12 of the ship, the inert gas line 71,73 that guides the inert gas to the vent mast 11,12, and the processing circuit 8 that closes the inert gas supply valve 72,74 provided in the inert gas line 71,73 during normal operation and opens the inert gas supply valve when the flammable gas is released from the vent mast 11,12.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a gas fuel supply system onboard a marine vessel. [Background technology]

[0002] Some ships are equipped with gas consumers that consume gas fuel to generate power or electricity. Examples of gas consumers include reciprocating engines, gas turbine engines, boilers, and fuel cells. A ship may be equipped with one or more gas consumers of the same type, or with multiple gas consumers of different types. Reciprocating engines and gas turbine engines drive propellers or generators, boilers supply steam to steam turbines that drive generators or to heated equipment, and fuel cells generate onboard electricity. Such ships are also equipped with gas fuel supply systems that supply gas fuel derived from liquefied gas to the gas consumers.

[0003] For example, Patent Document 1 discloses a gas fuel supply system that vaporizes LNG in a vaporizer and supplies it to an engine. In the gas fuel supply system of Patent Document 1, a main gas valve is provided between the vaporizer and the engine in a gas fuel supply line that connects a storage tank and an engine, and a vent line branches off from the gas fuel supply line upstream of the main gas valve and connects to a vent mast. When the supply pressure to the engine exceeds a set pressure, the main gas valve closes, and the vaporized LNG is discharged to the vent mast through the vent line. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2018-505987 Summary of the Invention [Problem to be solved by the invention]

[0005] When flammable gas is released into the atmosphere from the vent mast as in the gas fuel supply system of Patent Document 1, there is a risk that the flame of the flammable gas that has ignited in the atmosphere outside the vent mast may backfire into the vent mast or ignite inside the vent mast. One way to prevent these phenomena is to constantly supply inert gas to the vent mast, but in this case, a large amount of inert gas would be used.

[0006] Therefore, an object of the present disclosure is to provide a fuel supply system that can prevent the flame of flammable gas that has ignited in the atmosphere outside the vent mast from flashing back into the vent mast or igniting itself within the vent mast, while reducing the amount of inert gas used. [Means for solving the problem]

[0007] From a first aspect, the present disclosure provides a gas fuel supply system to be installed on a ship and to supply gas fuel derived from liquefied gas to a gas consumer, the gas fuel supply system comprising: a tank for storing the liquefied gas; a gas fuel supply line for drawing out the liquefied gas from the tank and guiding the vaporized gas produced by evaporation of the liquefied gas to the gas consumer as the gas fuel; a discharge line for guiding flammable gas, which is at least one of boil-off gas generated in the tank and the gas fuel remaining in the gas fuel supply line, to a vent mast of the ship; an inert gas line provided with an inert gas supply valve for guiding inert gas to the vent mast; and a processing circuit for closing the inert gas supply valve during normal operation and for opening the inert gas supply valve when the flammable gas is released from the vent mast.

[0008] From a second aspect, the present disclosure provides a gas fuel supply system to be installed on a ship and to supply gas fuel derived from liquefied gas to a gas consumer, the gas fuel supply system comprising: a tank for storing the liquefied gas; a gas fuel supply line for drawing out the liquefied gas from the tank and guiding the vaporized gas produced by evaporation of the liquefied gas to the gas consumer as the gas fuel; a discharge line for guiding flammable gas, which is at least one of boil-off gas generated in the tank and the gas fuel remaining in the gas fuel supply line, to a vent mast of the ship; an inert gas line provided with an inert gas supply valve for guiding inert gas to the vent mast; a concentration detector for detecting the flammable gas concentration in the vent mast; and a processing circuit for opening the inert gas supply valve when the flammable gas concentration detected by the concentration detector exceeds a threshold value.

[0009] From a third aspect, the present disclosure provides a gas fuel supply system to be installed on a ship and to supply gas fuel derived from liquefied gas to a gas consumer, the gas fuel supply system comprising: a tank for storing the liquefied gas; a gas fuel supply line for drawing out the liquefied gas from the tank and guiding the vaporized gas obtained by vaporizing the liquefied gas to the gas consumer as the gas fuel; a discharge line for guiding flammable gas, which is at least one of boil-off gas generated in the tank and the gas fuel remaining in the gas fuel supply line, to a vent mast of the ship; an inert gas line provided with an inert gas supply valve for guiding inert gas to the vent mast; a concentration detector for detecting an oxygen concentration in the vent mast; and a processing circuit for opening the inert gas supply valve to create an inert gas atmosphere inside the vent mast and then closing the inert gas supply valve, and thereafter opening the inert gas supply valve when the oxygen concentration detected by the concentration detector exceeds a first threshold value, and closing the inert gas supply valve when the oxygen concentration detected by the concentration detector falls below a second threshold value. [Effects of the Invention]

[0010] According to the present disclosure, a fuel supply system is provided that can prevent a flame of flammable gas that has ignited in the atmosphere outside the vent mast from flashing back into the vent mast or igniting within the vent mast, while reducing the amount of inert gas used. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic configuration diagram of a gas fuel supply system according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] 1 shows a gas fuel supply system 1 according to one embodiment. In this embodiment, the gas fuel supply system 1 is mounted on a ship together with a first gas consumer 4A and a second gas consumer 4B. The ship also has an inert gas supplier 7 mounted thereon, and includes a first vent mast 11 for a tank and a second vent mast 12 for the gas consumers.

[0013] The gas fuel supply system 1 may be entirely disposed below the open deck of the ship, or a portion of it may be disposed below the open deck and the remainder may be disposed above the open deck. The first vent mast 11 and the second vent mast 12 are provided on the open deck of the ship so as to extend upward from the open deck.

[0014] The gas fuel supply system 1 supplies gas fuel derived from liquefied gas to the first gas consumer 4A, and also supplies boil-off gas generated in a tank 2 (described later) to the second gas consumer 4B. Furthermore, the gas fuel supply system 1 can supply the boil-off gas as gas fuel to the first gas consumer 4A.

[0015] The liquefied gas is not particularly limited, but examples thereof include liquefied hydrogen, LNG (Liquefied Natural Gas), and LPG (Liquefied Petroleum Gas).

[0016] The first gas consumer 4A consumes gas fuel to generate propulsion power or propulsion or onboard electricity. In this embodiment, the first gas consumer 4A is an engine. The engine may be a reciprocating engine or a gas turbine engine. However, the first gas consumer 4A may also be a boiler, a fuel cell, or the like.

[0017] The second gas consumer 4B can consume and process excess boil-off gas that is not consumed as gas fuel and is retained in the tank 2, and is used to adjust the pressure inside the tank 2. In this embodiment, the second gas consumer 4B is a GCU (Gas Combustion Unit). However, if the first gas consumer 4A is a boiler, the excess boil-off gas may be processed by the first gas consumer 4A, and the second gas consumer 4B, which is a GCU, may be omitted.

[0018] The gas fuel supply system 1 includes a tank 2 that stores liquefied gas, a gas fuel supply line 3 that connects the tank 2 to a first gas consumer 4A, and a boil-off gas supply line 5 that connects the tank 2 to a second gas consumer 4B. The gas fuel supply system 1 further includes a relay line 54 that connects the boil-off gas supply line 5 and the gas fuel supply line 3.

[0019] In this embodiment, the tank 2 is a double-shelled tank including an inner tank 21 and an outer tank 22. A vacuum layer is formed between the inner tank 21 and the outer tank 22. However, the tank 2 may be a single-shelled tank covered with a heat insulating material, or may be a triple-shelled tank. Also, in this embodiment, the tank 2 is horizontally cylindrical. However, the tank 2 may also be vertically cylindrical. Alternatively, the tank 2 may be spherical or approximately rectangular.

[0020] The gas fuel supply line 3 leads the liquefied gas from the tank 2 and leads the vaporized gas obtained by vaporizing the liquefied gas as gas fuel to the first gas consumer 4A. In the tank 2, boil-off gas (BOG) is generated due to evaporation of the liquefied gas.

[0021] In this embodiment, a pump 31, a liquefied gas fuel heater 32, a main gas fuel valve 33, and a GVU (Gas Valve Unit) 34 are provided in this order from the upstream side on the gas fuel supply line 3. However, instead of the pump 31, a pressurizing device may be used that draws liquefied gas from the tank 2, vaporizes it, and returns the vaporized gas to the tank 2 to pressurize the inside of the tank 2.

[0022] The liquefied gas fuel heater 32 is a heat exchanger that heats and vaporizes the liquefied gas by exchanging heat between the liquefied gas and a heating medium, and heats the gas fuel, which is the vaporized gas obtained by vaporizing the liquefied gas, to the required temperature of the first gas consumer 4A. The heating medium is, for example, antifreeze, hot water, steam, or thermal oil.

[0023] Depending on the type of liquefied gas, the liquefied gas may become gas fuel in a subcritical or supercritical state when pressurized by the pump 31. In this case, the liquefied gas fuel heater 32 heats the gas fuel in a subcritical or supercritical state.

[0024] The GVU 34 includes multiple valves connected in series. The main gas fuel valve 33 may be included in the GVU 34. The main gas fuel valve 33 and the multiple valves included in the GVU 34 are controlled by a processing circuit 8. Note that in FIG. 1, some signal lines are omitted for simplicity.

[0025] The boil-off gas supply line 5 guides the boil-off gas from the tank 2 to the second gas consumer 4B. In this embodiment, a boil-off gas heater 51, a main gas fuel valve 52, and a GVU 53 are provided in this order from the upstream side on the boil-off gas supply line 5.

[0026] The boil-off gas heater 51 is a heat exchanger that exchanges heat between the boil-off gas and a heating medium to heat the boil-off gas to a temperature suitable for processing in the second gas consumer 4B. The GVU 53 includes multiple valves connected in series. The main gas fuel valve 52 may be included in the GVU 53. The main gas fuel valve 52 and the multiple valves included in the GVU 53 are controlled by the processing circuit 8.

[0027] The relay line 54 branches off from the boil-off gas supply line 5 upstream of the boil-off gas heater 51 and is connected to the gas fuel supply line 3 between the pump 31 and the liquefied gas fuel heater 32. An on-off valve 56 and a compressor 55 are provided in this order from upstream to downstream on the relay line 54. Note that if a pressurizing device is used to pressurize the inside of the tank 2 and the pressure inside the tank 2 is controlled to be high, the compressor 55 can be omitted.

[0028] Furthermore, the gas fuel supply system 1 includes a plurality of discharge lines 6, a first inert gas line 71, and a second inert gas line 73. Some of the plurality of discharge lines 6 lead flammable gas, which is boil-off gas generated in the tank 2 or gas fuel remaining in the gas fuel supply line 3, to the first vent mast 11, and the remaining plurality of discharge lines 6 lead flammable gas, which is gas fuel remaining in the gas fuel supply line 3 or the boil-off gas supply line 5, to the second vent mast 12. The first inert gas line 71 leads inert gas from the inert gas supplier 7 to the first vent mast 11, and the second inert gas line 73 leads inert gas from the inert gas supplier 7 to the second vent mast 12.

[0029] In this embodiment, the inert gas is nitrogen or carbon dioxide, and the inert gas supplier 7 is a bottle or cylinder that stores nitrogen or carbon dioxide. However, the inert gas supplier 7 may also be an inert gas generator that separates nitrogen from air. Alternatively, the inert gas may be argon or another gas other than nitrogen or carbon dioxide.

[0030] The first inert gas line 71 and the second inert gas line 73 are provided with inert gas supply valves 72 and 74, respectively. The inert gas supply valves 72 and 74 are controlled by the processing circuit 8.

[0031] The multiple discharge lines 6 include a tank discharge line 6A, gas fuel discharge lines 6B and 6E, and boil-off gas discharge lines 6C and 6D. The tank discharge line 6A guides boil-off gas from the tank 2 to the first vent mast 11. The tank discharge line 6A is provided with a pressure relief valve 61 that opens when the pressure in the tank 2 exceeds a set value.

[0032] The gas fuel discharge line 6E branches off from the gas fuel supply line 3 upstream of the main gas fuel valve 33 and connects to the first vent mast 11. In this embodiment, the downstream portion of the gas fuel discharge line 6E is a common line with the downstream portion of the tank discharge line 6A, but they may be separate. A pressure relief valve 65 is provided in the gas fuel discharge line 6E. Gas fuel may be present in a liquid state in the gas fuel supply line 3. The pressure relief valve 65 opens when gas fuel is trapped in a liquid state in a pipe that is isolated by closing a valve that constitutes the gas fuel supply line 3, and the liquid fuel expands and vaporizes due to external heat input, causing an increase in pressure in the pipe that constitutes the gas fuel supply line 3.

[0033] The gas fuel discharge line 6B branches off from the gas fuel supply line 3 downstream of the main gas fuel valve 33 and is connected to the second vent mast 12. In this embodiment, the gas fuel discharge line 6B branches off from the gas fuel supply line 3 inside the GVU 34. However, the gas fuel discharge line 6B may also branch off from the gas fuel supply line 3 upstream or downstream of the GVU 34.

[0034] The gas fuel discharge line 6B is provided with an on-off valve 62. In this embodiment, the on-off valve 62 is controlled by the processing circuit 8, but the on-off valve 62 may also be operated by a person.

[0035] The boil-off gas discharge line 6C branches off from the boil-off gas supply line 5 between the boil-off gas heater 51 and the main gas fuel valve 52 and is connected to the first vent mast 11. In this embodiment, the downstream portion of the boil-off gas discharge line 6C is a common line with the downstream portion of the gas fuel discharge line 6E and the downstream portion of the tank discharge line 6A, but they may be separate.

[0036] The boil-off gas discharge line 6C is provided with an on-off valve 63. The on-off valve 63 may be an automatic valve that opens when the pressure in the tank 2 or in the upstream portion of the boil-off gas heater 51 in the boil-off gas discharge line 6C exceeds a set value. Alternatively, the on-off valve 63 may be operated manually or controlled by the processing circuit 8.

[0037] An advantage of providing the boil-off gas discharge line 6C separately from the tank discharge line 6A is that the boil-off gas that is led to the first vent mast 11 through the boil-off gas discharge line 6C is heated in the boil-off gas heater 51 beforehand, so that the density of the boil-off gas released from the first vent mast 11 is reduced and the boil-off gas can be quickly diffused upward from the first vent mast 11. Furthermore, when the pressure inside the tank 2 exceeds a set value, the pressure relief valve 61 opens and the boil-off gas, which is difficult to diffuse at a low temperature, is released from the first vent mast 11 at a predetermined flow rate through the tank discharge line 6A. However, when the boil-off gas discharge line 6C is provided separately from the tank discharge line 6A, the boil-off gas, which is easy to diffuse at a high temperature, can be released from the first vent mast 11 at a controlled or adjusted flow rate according to the opening of the on-off valve 63 at any time and for any period or within any set pressure range of the tank 2, which is also an advantage.

[0038] The boil-off gas discharge line 6D branches off from the boil-off gas supply line 5 downstream of the main gas fuel valve 52 and is connected to the second vent mast 12. In this embodiment, the boil-off gas discharge line 6D branches off from the boil-off gas supply line 5 inside the GVU 53. However, the boil-off gas discharge line 6D may branch off from the boil-off gas supply line 5 upstream or downstream of the GVU 53.

[0039] The boil-off gas discharge line 6D is provided with an on-off valve 64. In this embodiment, the on-off valve 64 is controlled by the processing circuit 8, but the on-off valve 64 may also be operated by a person.

[0040] Furthermore, the gas fuel supply system 1 includes a purge line 75 for purging a portion of the gas fuel supply line 3 with an inert gas, and a purge line 77 for purging a portion of the boil-off gas supply line 5 with an inert gas. The purge line 75 guides the inert gas supplied from the inert gas supplier 7 to the gas fuel supply line 3 downstream of the main gas fuel valve 33. The purge line 77 guides the inert gas supplied from the inert gas supplier 7 to the boil-off gas supply line 5 downstream of the main gas fuel valve 52.

[0041] In this embodiment, the purge line 75 branches off from the first inert gas line 71 and connects to the gas fuel supply line 3 inside the GVU 34, and the purge line 77 branches off from the first inert gas line 71 and connects to the boil-off gas supply line 5 inside the GVU 53. However, the purge line 75 may be connected to the gas fuel supply line 3 on the upstream or downstream side of the GVU 34, and the purge line 77 may be connected to the boil-off gas supply line 5 on the upstream or downstream side of the GVU 53. Furthermore, the purge lines 75 and 77 do not need to branch off from the first inert gas line 71, and may extend from the inert gas supplier 7.

[0042] The purge lines 75 and 77 are provided with inert gas supply valves 76 and 78, respectively. The inert gas supply valves 76 and 78 are controlled by the processing circuit 8.

[0043] As described above, the processing circuit 8 controls various valves. A control device may be provided for each device such as the first gas consumer 4A, the second gas consumer 4B, the inert gas supplier 7, and the GVUs 34 and 53, and the processing circuit 8 may be configured by these control devices that can communicate with each other.

[0044] With respect to processing circuitry 8, the functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, application-specific integrated circuits (ASICs), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or processor.

[0045] The processing circuit 8 is electrically connected to a pressure detector 91 and concentration detectors 92 and 93. The pressure detector 91 detects the pressure inside the tank 2. In this embodiment, the pressure detector 91 detects the pressure of the gas phase, which is the portion above the liquid level of the liquefied gas inside the tank 2, but the pressure detector 91 may also detect the pressure of the liquid phase, which is the portion below the liquid level. The concentration detector 92 detects the concentration of flammable gas inside the first vent mast 11, and the concentration detector 93 detects the concentration of flammable gas inside the second vent mast 12.

[0046] Next, the valve control performed by the processing circuit 8 will be described.

[0047] With regard to the main gas fuel valve 33, the processing circuit 8 opens the main gas fuel valve 33 when gas fuel is to be supplied to the first gas consumer 4A, and closes the main gas fuel valve 33 in other cases.

[0048] With regard to the main gas fuel valve 52, the processing circuit 8 closes the main gas fuel valve 52 when the pressure detected by the pressure detector 91 is lower than a first set value α1, and opens the main gas fuel valve 52 when the pressure detected by the pressure detector 91 is higher than a second set value α2 that is higher than the first set value α1. The second set value α2 is lower than the set value of pressure at which the pressure relief valve 61 opens. Note that the main gas fuel valve 52 does not necessarily have to be controlled by the processing circuit 8, and may be operated manually to adjust the pressure in the tank 2 within a desired range.

[0049] Regarding the inert gas supply valves 72, 74, the processing circuit 8 closes the inert gas supply valves 72, 74 during normal operation, opens the inert gas supply valve 72 when flammable gas, which is at least one of boil-off gas and gas fuel, is discharged into the atmosphere from the first vent mast 11, and opens the inert gas supply valve 74 when flammable gas, which is at least one of gas fuel and boil-off gas, is discharged into the atmosphere from the second vent mast 12. Normal operation includes times when the ship is sailing, when at anchor, and when loading and unloading if the ship is a cargo carrier.

[0050] In this way, when flammable gas is released from the first vent mast 11 or the second vent mast 12, the inert gas supply valve 72 provided on the first inert gas line 71 or the inert gas supply valve 74 provided on the second inert gas line 73 is opened, so it is possible to prevent the flame of flammable gas that has ignited in the atmosphere outside the first vent mast 11 and the second vent mast 12 from flashing back into the first vent mast 11 and the second vent mast 12 or ignition within the first vent mast 11 and the second vent mast 12, while reducing the amount of inert gas used.

[0051] In this embodiment, the inert gas supply valves 72 and 74 are flow control valves. When opening the inert gas supply valve 72, the processing circuit 8 adjusts the aperture of the inert gas supply valve 72 based on the flammable gas concentration detected by the concentration detector 92. That is, the processing circuit 8 adjusts the aperture of the inert gas supply valve 72 so that the flammable gas concentration in the first vent mast 11 is maintained at or below a predetermined value. Similarly, when opening the inert gas supply valve 74, the processing circuit 8 adjusts the aperture of the inert gas supply valve 74 based on the flammable gas concentration detected by the concentration detector 93. That is, the processing circuit 8 adjusts the aperture of the inert gas supply valve 74 so that the flammable gas concentration in the second vent mast 12 is maintained at or below a predetermined value. This control can further reduce the amount of inert gas used.

[0052] As for the specific timing for opening the inert gas supply valve 72, the processing circuit 8 opens the inert gas supply valve 72 when the pressure detected by the pressure detector 91 exceeds a threshold value β. The threshold value β is greater than the second set value α2 for opening and closing the main gas fuel valve 52 described above. If the threshold value β is set to a pressure lower than the pressure at which the pressure relief valve 61 opens, the supply of inert gas can be started before the boil-off gas is led to the first vent mast 11 through the tank discharge line 6A.

[0053] In this embodiment, a temperature detector 94 that detects the temperature of the downstream portion of the tank discharge line 6A is provided downstream of the pressure relief valve 61 in the tank discharge line 6A. When the temperature detected by the temperature detector 94 falls below a threshold value, the processing circuit 8 may determine that a leak has occurred in the pressure relief valve 61 and open the inert gas supply valve 72.

[0054] Furthermore, the processing circuit 8 opens the inert gas supply valve 72 when or before the on-off valve 63 provided in the boil-off gas discharge line 6C opens. With this configuration, the supply of inert gas can be started simultaneously with or before the boil-off gas is led to the first vent mast 11 through the boil-off gas discharge line 6C. As described above, if the on-off valve 63 is an automatic valve, the on-off valve 63 opens when the pressure in the tank 2 or in the upstream portion of the boil-off gas heater 51 in the boil-off gas discharge line 6C exceeds a set value.

[0055] As for the specific timing for opening the inert gas supply valve 74, the processing circuit 8 opens the inert gas supply valve 74 when or before the on-off valve 62 provided in the gas fuel discharge line 6B opens, and when or before the on-off valve 64 provided in the boil-off gas discharge line 6D opens. With this configuration, the supply of inert gas can be started simultaneously with or before the gas fuel remaining in the gas fuel supply line 3 is led to the second vent mast 12 through the gas fuel discharge line 6B, and the supply of inert gas can be started simultaneously with or before the boil-off gas is led to the second vent mast 12 through the boil-off gas discharge line 6D.

[0056] When purging a portion of the gas fuel supply line 3 with an inert gas, the processing circuit 8 opens the on-off valve 62 and then opens the inert gas supply valve 76. Therefore, the processing circuit 8 may determine that the on-off valve 62 has not yet been opened when the processing circuit 8 receives a purge start signal for the gas fuel supply line 3. Similarly, when purging a portion of the boil-off gas supply line 5 with an inert gas, the processing circuit 8 opens the on-off valve 64 and then opens the inert gas supply valve 78. Therefore, the processing circuit 8 may determine that the on-off valve 64 has not yet been opened when the processing circuit 8 receives a purge start signal for the boil-off gas supply line 5.

[0057] <Modification> The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present disclosure.

[0058] For example, the processing circuit 8 may close the inert gas supply valve 72 when the flammable gas concentration detected by the concentration detector 92 is below a threshold value γ1, and open the inert gas supply valve 72 when the flammable gas concentration detected by the concentration detector 92 exceeds the threshold value γ1. For example, the threshold value γ1 is set to a value slightly lower than the lower explosive limit (LEL).

[0059] In this way, if the inert gas supply valve 72 provided on the first inert gas line 71 is opened when the flammable gas concentration in the first vent mast 11 exceeds the threshold value γ1, it is possible to prevent the flame of the flammable gas that has ignited in the atmosphere outside the first vent mast 11 from backfiring into the first vent mast 11 or igniting itself within the first vent mast 11, while reducing the amount of inert gas used.

[0060] After opening the inert gas supply valve 72, the processing circuit 8 adjusts the opening degree of the inert gas supply valve 72 based on the flammable gas concentration detected by the concentration detector 92, as in the previous embodiment, thereby further reducing the amount of inert gas used.

[0061] Similarly, the processing circuit 8 may close the inert gas supply valve 74 when the flammable gas concentration detected by the concentration detector 93 is below the threshold value γ2, and may open the inert gas supply valve 74 when the flammable gas concentration detected by the concentration detector 93 is above the threshold value γ2. For example, the threshold value γ2 is set to a value slightly lower than the lower explosive limit (LEL).

[0062] In this way, if the inert gas supply valve 74 provided on the second inert gas line 73 is opened when the flammable gas concentration in the second vent mast 12 exceeds the threshold value γ2, it is possible to prevent the flame of the flammable gas that has ignited in the atmosphere outside the second vent mast 12 from backfiring into the second vent mast 12 or igniting itself within the second vent mast 12, while reducing the amount of inert gas used.

[0063] After opening the inert gas supply valve 74, the processing circuit 8 adjusts the opening degree of the inert gas supply valve 74 based on the flammable gas concentration detected by the concentration detector 93, as in the previous embodiment, thereby further reducing the amount of inert gas used.

[0064] The concentration detector 92 may detect the oxygen concentration in the first vent mast 11. In this case, the processing circuit 8 may open the inert gas supply valve 72 to create an inert gas atmosphere inside the first vent mast 11, then close the inert gas supply valve 72. Thereafter, the processing circuit 8 may open the inert gas supply valve 72 when the oxygen concentration detected by the concentration detector 92 exceeds the first threshold value γ3, and close the inert gas supply valve 72 again when the oxygen concentration detected by the concentration detector 92 falls below the second threshold value γ4. For example, the first threshold value γ3 may be set to a value slightly lower than the explosive limit oxygen concentration of the flammable gas in the inert gas atmosphere. The second threshold value γ4 may be lower than or equal to the first threshold value γ3. This configuration also makes it possible to prevent backfire into the first vent mast 11 of a flame of flammable gas ignited in the atmosphere outside the first vent mast 11 or ignition within the first vent mast 11 while reducing the amount of inert gas used.

[0065] Similarly, the concentration detector 93 may detect the oxygen concentration in the second vent mast 12. In this case, the processing circuit 8 may open the inert gas supply valve 74 to create an inert gas atmosphere inside the second vent mast 12, then close the inert gas supply valve 74. Thereafter, the processing circuit 8 may open the inert gas supply valve 74 when the oxygen concentration detected by the concentration detector 93 exceeds the first threshold value γ5, and close the inert gas supply valve 74 again when the oxygen concentration detected by the concentration detector 93 falls below the second threshold value γ6. For example, the first threshold value γ5 may be set to a value slightly lower than the explosive limit oxygen concentration of the flammable gas in the inert gas atmosphere. The second threshold value γ6 may be lower than the first threshold value γ5 or may be equal to the first threshold value γ5. This configuration also makes it possible to prevent backfire into the second vent mast 12 or ignition within the second vent mast 12 of a flame of flammable gas ignited in the atmosphere outside the second vent mast 12 while reducing the amount of inert gas used.

[0066] Also, the ship may include only the first vent mast 11 without the second vent mast 12, and the gas fuel discharge line 6B and the boil-off gas discharge line 6D may be connected to the first vent mast 11. However, if there is a first vent mast 11 for the tank and a second vent mast 12 for the gas consuming machine as in the above embodiment, the supply of inert gas can be managed separately, making it easier to control the inert gas.

[0067] The inert gas supply valves 72 and 74 do not necessarily have to be flow control valves, but may be simple on-off valves.

[0068] <Oversight> In a first aspect, the present disclosure provides, from a first aspect, a gas fuel supply system to be installed on a ship and to supply gas fuel derived from liquefied gas to a gas consumer, the gas fuel supply system comprising: a tank to store the liquefied gas; a gas fuel supply line to discharge the liquefied gas from the tank and to guide the vaporized gas of the liquefied gas to the gas consumer as the gas fuel; a discharge line to guide flammable gas, which is at least one of boil-off gas generated in the tank and the gas fuel remaining in the gas fuel supply line, to a vent mast of the ship; an inert gas line provided with an inert gas supply valve to guide inert gas to the vent mast; and a processing circuit to close the inert gas supply valve during normal operation and to open the inert gas supply valve when the flammable gas is released from the vent mast.

[0069] According to the above configuration, when flammable gas is released from the vent mast, the inert gas supply valve provided in the inert gas line is opened, so that it is possible to reduce the amount of inert gas used while preventing the flame of flammable gas that has ignited in the atmosphere outside the vent mast from backfiring into the vent mast or igniting itself within the vent mast.

[0070] In a second aspect, in the first aspect, the discharge line includes a tank discharge line provided with a pressure relief valve that directs the boil-off gas from the tank to the vent mast, and the gas fuel supply system further includes a pressure detector that detects the pressure in the tank, and the processing circuit may open the inert gas supply valve when the pressure detected by the pressure detector exceeds a threshold value. According to this configuration, by setting the threshold value to a pressure lower than the pressure at which the pressure relief valve opens, the supply of inert gas can be started before the boil-off gas is directed to the vent mast through the tank discharge line.

[0071] In a third aspect, in the first or second aspect, the gas fuel supply line may be provided with a liquefied gas fuel heater and a main gas fuel valve provided downstream of the liquefied gas fuel heater, the discharge line may include a gas fuel discharge line provided with an on-off valve that branches off from the gas fuel supply line downstream of the main gas fuel valve and leads to the vent mast, and the processing circuit may open the inert gas supply valve when or before the on-off valve opens. With this configuration, the supply of inert gas can be started simultaneously with or before the gas fuel remaining in the gas fuel supply line is led to the vent mast through the gas fuel discharge line.

[0072] In a fourth aspect, the vent mast in the third aspect may include a first vent mast and a second vent mast, the discharge line may include a tank discharge line equipped with a pressure relief valve that directs the boil-off gas from the tank to the first vent mast, and the gas fuel discharge line may be connected to the second vent mast. The first vent mast is for the tank, and the second vent mast is for the gas consumer. If there is a first vent mast for the tank and a second vent mast for the gas consumer in this way, the supply of inert gas can be managed separately, making it easier to control the inert gas.

[0073] In a fifth aspect, in any of the first to fourth aspects, the gas consumer is a first gas consumer, and the gas fuel supply system further includes a boil-off gas supply line provided with a boil-off gas heater that guides the boil-off gas from the tank to a second gas consumer and a main gas fuel valve downstream of the boil-off gas heater, the discharge line includes a boil-off gas discharge line that branches off from the boil-off gas supply line between the boil-off gas heater and the main gas fuel valve and leads to the vent mast and is provided with an on-off valve, and the processing circuit may open the inert gas supply valve when or before the on-off valve opens. With this configuration, the supply of inert gas can be started simultaneously with or before the boil-off gas is guided to the vent mast through the boil-off gas discharge line.

[0074] As a sixth aspect, in any of the first to fifth aspects, the gas consumer is a first gas consumer, and the gas fuel supply system further includes a boil-off gas supply line provided with a boil-off gas heater that guides the boil-off gas from the tank to a second gas consumer and a main gas fuel valve downstream of the boil-off gas heater, the discharge line includes a boil-off gas discharge line that branches off from the boil-off gas supply line downstream of the main gas fuel valve and leads to the vent mast and is provided with an on-off valve, and the processing circuit may open the inert gas supply valve when or before the on-off valve opens. With this configuration, the supply of inert gas can be started simultaneously with or before the boil-off gas is guided to the vent mast through the boil-off gas discharge line.

[0075] In a seventh aspect, in any of the first to sixth aspects, the inert gas supply valve is a flow control valve, and the gas fuel supply system further includes a concentration detector that detects the flammable gas concentration in the vent mast, and the processing circuit adjusts the opening of the inert gas supply valve based on the flammable gas concentration detected by the concentration detector when opening the inert gas supply valve. With this configuration, the amount of inert gas used can be further reduced.

[0076] As an eighth aspect, in any of the first to seventh aspects, for example, the inert gas line guides the inert gas from an inert gas supplier to the vent mast, the inert gas being nitrogen or carbon dioxide, and the inert gas supplier may be a bottle or cylinder that stores nitrogen or carbon dioxide, or an inert gas generator that separates nitrogen from air.

[0077] In a ninth aspect, from a second aspect, the present disclosure provides a gas fuel supply system to be installed on a ship and to supply gas fuel derived from liquefied gas to a gas consumer, the gas fuel supply system comprising: a tank for storing the liquefied gas; a gas fuel supply line for drawing out the liquefied gas from the tank and guiding the vaporized gas produced by evaporation of the liquefied gas to the gas consumer as the gas fuel; a discharge line for guiding flammable gas, which is at least one of boil-off gas generated in the tank and the gas fuel remaining in the gas fuel supply line, to a vent mast of the ship; an inert gas line provided with an inert gas supply valve for guiding inert gas to the vent mast; a concentration detector for detecting the flammable gas concentration in the vent mast; and a processing circuit for opening the inert gas supply valve when the flammable gas concentration detected by the concentration detector exceeds a threshold value.

[0078] According to the above configuration, when the flammable gas concentration inside the vent mast exceeds the threshold value, the inert gas supply valve provided in the inert gas line is opened, thereby making it possible to reduce the amount of inert gas used and prevent the flame of flammable gas that has ignited in the atmosphere outside the vent mast from backfiring into the vent mast or igniting itself inside the vent mast.

[0079] In a tenth aspect, in the ninth aspect, the inert gas supply valve may be a flow control valve, and the processing circuit may adjust the opening of the inert gas supply valve based on the flammable gas concentration detected by the concentration detector when opening the inert gas supply valve. With this configuration, the amount of inert gas used can be further reduced.

[0080] From a third aspect, the present disclosure provides a gas fuel supply system for supplying gas fuel derived from liquefied gas to a gas consumer, the gas fuel supply system comprising: a tank for storing the liquefied gas; a gas fuel supply line for drawing out the liquefied gas from the tank and leading the vaporized gas obtained by vaporizing the liquefied gas to the gas consumer as the gas fuel; a discharge line for leading flammable gas, which is at least one of boil-off gas generated in the tank and the gas fuel remaining in the gas fuel supply line, to a vent mast of the ship; an inert gas line provided with an inert gas supply valve for leading inert gas to the vent mast; a concentration detector for detecting an oxygen concentration in the vent mast; and a processing circuit for opening the inert gas supply valve to create an inert gas atmosphere inside the vent mast and then closing the inert gas supply valve, and thereafter opening the inert gas supply valve when the oxygen concentration detected by the concentration detector exceeds a first threshold value, and closing the inert gas supply valve when the oxygen concentration detected by the concentration detector falls below a second threshold value.

[0081] According to the above configuration, it is possible to reduce the amount of inert gas used while preventing the flame of flammable gas that has ignited in the atmosphere outside the vent mast from backfiring into the vent mast or igniting itself within the vent mast. [Explanation of symbols]

[0082] 1 Gas fuel supply system 11 No. 1 Bent Mast 12 No. 2 Bent Mast 2 Tanks 3 Gas fuel supply line 32 Liquefied gas fuel heater 33 Main gas fuel valve for first gas consumer 4A First gas consumer 4B Second gas consumer 5 Boil-off gas supply line 51 Boil-off gas heater 52 Main gas fuel valve for second gas consumer 6. Discharge line 6A Tank discharge line 6B, 6E Gas fuel discharge line 6C, 6D Boil-off gas discharge line 61,65 Pressure relief valve 62, 63, 64 On-off valve 71,73 Inert gas line 72, 74, 76, 78 Inert gas supply valve 75,77 Purge line 8 Processing Circuit 91 Pressure detector 92,93 Concentration detector

Claims

1. A gas fuel supply system installed on a ship that supplies gas fuel derived from liquefied gas to a gas consumer, a tank for storing the liquefied gas; a gas fuel supply line that draws out the liquefied gas from the tank and leads the vaporized gas obtained by vaporizing the liquefied gas to the gas consumer as the gas fuel; a discharge line for guiding flammable gas, which is at least one of boil-off gas generated in the tank and gas fuel remaining in the gas fuel supply line, to a vent mast of the ship; an inert gas line provided with an inert gas supply valve for introducing inert gas to the vent mast; a processing circuit that closes the inert gas supply valve during normal operation and opens the inert gas supply valve when the flammable gas is released from the vent mast; A gas fuel supply system comprising:

2. the discharge line includes a tank discharge line provided with a pressure relief valve that directs the boil-off gas from the tank to the vent mast; a pressure detector for detecting a pressure in the tank; The gas fuel supply system of claim 1 , wherein the processing circuit opens the inert gas supply valve when the pressure detected by the pressure detector exceeds a threshold value.

3. a liquefied gas fuel heater is provided in the gas fuel supply line, and a main gas fuel valve is provided downstream of the liquefied gas fuel heater; the discharge line includes a gas fuel discharge line provided with an on-off valve, branching from the gas fuel supply line downstream of the main gas fuel valve and leading to the vent mast, The gas fuel supply system according to claim 1 , wherein the processing circuit opens the inert gas supply valve when or before the on-off valve opens.

4. The vent mast includes a first vent mast and a second vent mast, the discharge line includes a tank discharge line provided with a pressure relief valve that directs the boil-off gas from the tank to the first vent mast; The gas fuel supply system of claim 3 , wherein the gas fuel discharge line leads to the second vent mast.

5. the gas consumer is a first gas consumer, a boil-off gas heater that guides the boil-off gas from the tank to a second gas consumer, and a boil-off gas supply line that is provided with a main gas fuel valve downstream of the boil-off gas heater; the discharge line includes a boil-off gas discharge line provided with an on-off valve, branching from the boil-off gas supply line between the boil-off gas heater and the main gas fuel valve and leading to the vent mast, The gas fuel supply system according to claim 1 , wherein the processing circuit opens the inert gas supply valve when or before the on-off valve opens.

6. the gas consumer is a first gas consumer, a boil-off gas heater that guides the boil-off gas from the tank to a second gas consumer, and a boil-off gas supply line that is provided with a main gas fuel valve downstream of the boil-off gas heater; the discharge line includes a boil-off gas discharge line provided with an on-off valve, branching from the boil-off gas supply line downstream of the main gas fuel valve and leading to the vent mast, The gas fuel supply system according to claim 1 , wherein the processing circuit opens the inert gas supply valve when or before the on-off valve opens.

7. the inert gas supply valve is a flow control valve; a concentration detector for detecting a flammable gas concentration in the vent mast; 7. The gas fuel supply system according to claim 1, wherein the processing circuit adjusts the opening degree of the inert gas supply valve based on the flammable gas concentration detected by the concentration detector when the inert gas supply valve is opened.

8. the inert gas line directs the inert gas from an inert gas supplier to the vent mast; the inert gas is nitrogen or carbon dioxide; 7. The gas fuel supply system according to claim 1, wherein the inert gas supplier is a bottle or cylinder that stores nitrogen or carbon dioxide, or an inert gas generator that separates nitrogen from air.

9. A gas fuel supply system installed on a ship that supplies gas fuel derived from liquefied gas to a gas consumer, a tank for storing the liquefied gas; a gas fuel supply line that draws out the liquefied gas from the tank and leads the vaporized gas obtained by vaporizing the liquefied gas to the gas consumer as the gas fuel; a discharge line for guiding flammable gas, which is at least one of boil-off gas generated in the tank and gas fuel remaining in the gas fuel supply line, to a vent mast of the ship; an inert gas line provided with an inert gas supply valve for introducing inert gas to the vent mast; a concentration detector that detects the concentration of flammable gas in the vent mast; a processing circuit that opens the inert gas supply valve when the flammable gas concentration detected by the concentration detector exceeds a threshold value; A gas fuel supply system comprising:

10. the inert gas supply valve is a flow control valve; The gas fuel supply system according to claim 9 , wherein the processing circuit adjusts the opening degree of the inert gas supply valve based on the combustible gas concentration detected by the concentration detector when the inert gas supply valve is opened.

11. A gas fuel supply system installed on a ship that supplies gas fuel derived from liquefied gas to a gas consumer, a tank for storing the liquefied gas; a gas fuel supply line that draws out the liquefied gas from the tank and leads the vaporized gas obtained by vaporizing the liquefied gas to the gas consumer as the gas fuel; a discharge line for guiding flammable gas, which is at least one of boil-off gas generated in the tank and gas fuel remaining in the gas fuel supply line, to a vent mast of the ship; an inert gas line provided with an inert gas supply valve for introducing inert gas to the vent mast; a concentration detector for detecting an oxygen concentration in the vent mast; a processing circuit that opens the inert gas supply valve to create an inert gas atmosphere inside the vent mast and then closes the inert gas supply valve, and thereafter opens the inert gas supply valve when the oxygen concentration detected by the concentration detector exceeds a first threshold value, and closes the inert gas supply valve when the oxygen concentration detected by the concentration detector falls below a second threshold value; A gas fuel supply system comprising:

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