Ship using methanol as fuel

Abstract

The present invention addresses the problem of providing a ship using methanol as fuel, which does not increase the equipment cost even if a methanol discharge tank is provided. When inert gas is supplied to the internal combustion engine (1) and the methanol supply system (MSS) by the inert gas supply unit (13), the methanol discharge system stops the discharge operation of the decompression discharge mechanism. When the inert gas is not supplied to the internal combustion engine (1) and the methanol supply system (MSS) by the inert gas supply unit (13), the decompression discharge mechanism is operated to discharge the gas in the reflux chamber (15) to the methanol discharge tank (17) at a pressure equal to or less than a predetermined pressure. The number of times the methanol discharge system supplies the inert gas to the internal combustion engine (1) and the methanol supply system (MSS) by the inert gas supply unit is determined such that the amount of residual methanol remaining in the internal combustion engine (1) and the methanol supply system (MSS) is less than a predetermined value.

Description

Technical Field

[0001] This invention relates to ships that use methanol as fuel. Background Technology

[0002] In Japanese Patent No. 6262076 (Patent Document 1) Figure 1 Patent Document 1 discloses a conventional methanol-fueled ship equipped with a methanol discharge system that discharges residual methanol from a methanol supply system that supplies methanol from a methanol fuel tank to the internal combustion engine during fuel switching. The conventional methanol-fueled ship includes: an internal combustion engine 11 located in the engine room and capable of operating on methanol as fuel; a methanol fuel tank 12 for storing methanol; a methanol supply system 13 for supplying methanol from the methanol fuel tank to the internal combustion engine; a valve unit 14 including multiple control valves that control the supply and amount of methanol supplied from the methanol fuel tank 12 to the internal combustion engine; an inert gas generation system 15 for generating an inert gas; and a methanol discharge system that uses the inert gas to discharge residual methanol from the internal combustion engine 11 and the methanol supply system 13 through a discharge line 24 to a methanol discharge tank 16. In the ship described in Patent Document 1, there is a problem that the discharged methanol cannot be reused.

[0003] Therefore, as in Japanese Patent No. 7357726 (Patent Document 2) Figure 1 As shown in the fuel supply device, an auxiliary tank 4 is proposed to be installed between the fuel tank 2 and the fuel supply system. The auxiliary tank 4 can mix the fuel (methanol) supplied from the fuel tank 2 via the fuel supply line with a portion of the fuel returned from the internal combustion engine via the fuel return line, thereby enabling the reuse of the purified fuel.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent No. 6262076

[0007] Patent Document 2: Japanese Patent No. 7357726 Summary of the Invention

[0008] The technical problem that the invention aims to solve

[0009] In, as in patent document 2 Figure 1 When the auxiliary tank is installed in the same way as the fuel supply device, the following problems arise: In addition to ensuring the location of the auxiliary tank, the auxiliary tank needs to be installed under the same conditions as the methanol fuel tank (fire extinguishing equipment, etc.), and the auxiliary tank also needs to be reinforced to withstand the pressure of inert gas (minimum 8 bar).

[0010] Furthermore, in a methanol discharge system, such as the invention in Patent Document 1, where residual methanol in the methanol supply system 13 is discharged together with inactive gas into the methanol discharge tank 16, there is a problem that the methanol discharge tank also needs to meet pressure resistance specifications, thus increasing equipment costs.

[0011] The purpose of this invention is to provide a ship that uses methanol as fuel without increasing equipment costs.

[0012] Solutions for solving technical problems

[0013] The present invention relates to a methanol-fueled ship comprising a methanol supply system and a methanol discharge system. The methanol supply system comprises: an internal combustion engine disposed in an engine room and capable of operating on methanol as fuel; a methanol fuel tank for storing methanol as fuel; and a methanol supply unit (LFSS) for supplying methanol from the methanol fuel tank to the internal combustion engine. Furthermore, the methanol discharge system comprises: an inert gas storage tank for storing inert gas; an inert gas supply unit for supplying (ejecting) inert gas from the inert gas storage tank to the internal combustion engine and the methanol supply system after the methanol supply system stops supplying methanol from the methanol fuel tank to the internal combustion engine; and a methanol discharge tank, wherein the methanol discharge system uses the inert gas supplied from the inert gas supply unit to the internal combustion engine and the methanol supply system to discharge residual methanol and inert gas remaining in the internal combustion engine and the methanol supply unit (LFSS) together via a return chamber into the methanol discharge tank.

[0014] The methanol discharge system used in this invention includes: a reflux chamber, which has a smaller capacity than the methanol discharge tank and temporarily stores residual methanol and inert gases discharged from the internal combustion engine and from the methanol supply unit (LFSS); and a pressure-reducing discharge mechanism that discharges residual methanol and inert gases from the reflux chamber to the methanol discharge tank at a pressure below a predetermined pressure. Furthermore, when the methanol discharge system supplies (ejects) inert gases to the internal combustion engine and the methanol supply system via the inert gas supply unit, the discharge operation of the pressure-reducing discharge mechanism is stopped. When inert gases are not supplied to the internal combustion engine and the methanol supply system via the inert gas supply unit, the pressure-reducing discharge mechanism operates to discharge the gas in the reflux chamber to the methanol discharge tank at a pressure below a predetermined pressure. The number of times the methanol discharge system supplies inert gases to the internal combustion engine and the methanol supply system via the inert gas supply unit is determined such that the amount of residual methanol remaining in the internal combustion engine and the methanol supply system is less than a predetermined value.

[0015] According to the present invention, when inert gas is supplied to the internal combustion engine and the methanol supply system via the inert gas supply unit, residual methanol remaining in the internal combustion engine and the methanol supply system is partially purified by the inert gas, and the purified residual methanol and inert gas are temporarily stored in the reflux chamber. Furthermore, a discharge operation is performed to discharge the temporarily stored residual methanol and inert gas in the reflux chamber to the methanol discharge tank at a pressure below a predetermined pressure. As a result, according to the present invention, there is no need to use the expensive methanol discharge tank with high pressure resistance as in the past, thereby significantly reducing equipment costs.

[0016] The inactive gas needs to be supplied to the internal combustion engine and methanol supply system at least twice via the inactive gas supply unit. The more times this is done, the smaller the capacity of the methanol emission tank becomes.

[0017] The methanol discharge system has a function to count the number of times (i) inert gas is supplied to the internal combustion engine and the methanol supply system via the inert gas supply section. This function can be implemented by setting a counter to count the number of times the on / off valve V0, located in the inert gas supply section and installed on the outlet side of the inert gas storage tank, is opened and closed, or by counting the opening and closing commands supplied to the on / off valve V0. When the number of times (i) reaches a predetermined number (n), the supply of inert gas to the internal combustion engine and the methanol supply system via the inert gas supply section is stopped, and the purification operation is shut down. Furthermore, when the pressure in the return chamber drops to a predetermined pressure, the operation of discharging residual methanol and inert gas from the return chamber to the methanol discharge tank is stopped.

[0018] It should be noted that the following actions can also be performed repeatedly: During the process of supplying (ejecting) inactive gas through the inactive gas supply section, when the pressure of the gas in the return chamber reaches a predetermined first set value, the supply of inactive gas to the internal combustion engine and the methanol supply system is stopped, and the pressure reducing and discharge mechanism is activated to discharge the gas in the return chamber to the methanol discharge tank at a pressure below a predetermined pressure. When the pressure of the gas in the return chamber drops to a second set value lower than the first set value, the operation of the pressure reducing and discharge mechanism is stopped, and the discharge action is stopped, until the number of times i reaches the predetermined number of times n.

[0019] It should be noted that, in specific examples, the methanol supply system may also include: a methanol supply device, which has the function of selectively supplying methanol from a methanol fuel tank or inert gas from an inert gas storage tank to the internal combustion engine, and the function of supplying residual methanol to the return chamber; a buffer tank, which is disposed between the methanol fuel tank and the methanol supply device and adjusts the pressure of the methanol supplied from the methanol fuel tank; a main on / off valve V, which controls the supply and stop of methanol from the methanol fuel tank; and a first valve group VT1, which is disposed between the methanol supply device and the internal combustion engine and controls the passage of methanol, residual methanol, and inert gas. It should be noted that, of course, the main on / off valve may not be used, and its function may be achieved by opening and closing a pump installed for the methanol fuel tank. Alternatively, the buffer tank may not be used, and a valve group including a pressure reducing valve may be used for pressure adjustment.

[0020] Furthermore, the pressure-reducing discharge mechanism of the methanol discharge system can be configured to include: a pressure gauge PS that measures the pressure in the reflux chamber; a second valve group VT2, which has a secondary on / off valve V2 between the methanol supply device and the reflux chamber; a third valve group VT3, which has a secondary on / off valve V3 between the internal combustion engine and the reflux chamber; a fourth valve group VT4, which includes a secondary on / off valve V4 and a pressure-reducing valve RV1 between the reflux chamber and the methanol discharge tank; and a valve controller that uses the output of the pressure gauge as input to control the secondary on / off valves V2 to V4 in the second to fourth valve groups. If the pressure-reducing discharge mechanism is configured in this way, it can be easily constructed.

[0021] Preferably, the third valve group VT3 includes a remotely operated valve PV that opens when purifying inactive gases. If the remotely operated valve PV is installed in the third valve group VT3, purification can be reliably implemented.

[0022] It should be noted that the values ​​of the first setting and the second setting can be determined by the design conditions, but it is preferred that the first setting is below 8 bar and the second setting is below 1 bar.

[0023] The storage capacity of the reflux chamber is preferably less than 1 / 10 of the capacity of the methanol discharge tank. Under such conditions, the first and second settings described above can be used. Attached Figure Description

[0024] Figure 1 This is a block diagram of the main parts of the fuel supply and exhaust system of the internal combustion engine of a ship that uses methanol as fuel, as described in this embodiment.

[0025] Figure 2 It is specifically shown Figure 1 A block diagram of the included valve groups.

[0026] Figure 3 This is a flowchart of the operation of the methanol discharge system.

[0027] Explanation of reference numerals in the attached figures

[0028] 1. Internal Combustion Engine

[0029] 3. Methanol fuel tank

[0030] 5. Buffer tank

[0031] 7 Main on / off valve

[0032] 9. Methanol supply unit

[0033] 11. Inactive gas storage tank

[0034] 13. Inactive Gas Supply Department

[0035] 15 Reflux chamber

[0036] 17 Methanol Discharge Tank

[0037] MSS Methanol Supply System

[0038] MDS Methanol Discharge System

[0039] RMD pressure relief mechanism

[0040] VT1 First Valve Group

[0041] VT2 Second Valve Group

[0042] VT3 Third Valve Group

[0043] VT4 Fourth Valve Group

[0044] PS pressure gauge

[0045] VC valve controller. Detailed Implementation

[0046] Hereinafter, an example of an embodiment of the ship using methanol as fuel according to the present invention will be described in detail with reference to the accompanying drawings. Figure 1 This is a block diagram of the main components of the fuel supply and exhaust system for the internal combustion engine of a ship using methanol as fuel, as described in this embodiment. Additionally, Figure 2 It is specifically shown Figure 1 A block diagram of all included valve assemblies. Furthermore, Figure 3This is a flowchart of the operation of the methanol discharge system. The methanol supply and discharge system of the ship using methanol as fuel in this embodiment generally includes: a methanol supply system MSS, which supplies methanol from the methanol fuel tank 3 to the internal combustion engine 1 located in the engine room and capable of operating with methanol as fuel; and a methanol discharge system MDS, which discharges (purifies) the methanol remaining in the methanol supply system MSS using an inactive gas (nitrogen in this example) stored in the inactive gas storage tank 11 when the internal combustion engine 1 is switching fuels.

[0047] The methanol supply system (MSS) is configured to control the supply and quantity of methanol from the methanol fuel tank 3 to the internal combustion engine 1. The MSS used in this embodiment includes a buffer tank 5, a main on / off valve 7, and a first valve group VT1. The buffer tank 5 is located between the methanol fuel tank 3 and the methanol supply device 9, and adjusts the pressure of the methanol supplied from the methanol fuel tank 3. The main on / off valve 7 controls the supply and stop of methanol from the methanol fuel tank 3. Furthermore, the methanol supply device 9 has the following functions: supplying methanol from the methanol fuel tank 3 to the internal combustion engine 1 via the first valve group; and, during fuel switching, supplying a portion of the inert gas supplied from the inert gas storage tank 11, along with residual methanol, to the return chamber 15 (described later) via the second valve group VT2. It should be noted that the first valve group VT1 includes: a secondary on / off valve for controlling the methanol supply; and a secondary on / off valve for controlling the discharge of a portion of the inert gas supplied from the inert gas storage tank 11 and residual methanol to the methanol supply device 9 during fuel switching. In addition, the first valve group VT1 has an arbitrary structure, which includes a secondary opening and closing valve for controlling the discharge of a portion of the inactive gas supplied from the inactive gas storage tank 11 and residual methanol through the internal combustion engine 1 to the return chamber 15 during fuel switching.

[0048] When the internal combustion engine 1 undergoes fuel switching, the auxiliary on / off valve in the first valve group VT1 closes to prevent methanol from being supplied to the internal combustion engine 1, while other auxiliary on / off valves open to allow inactive gases to be supplied to the internal combustion engine 1. Additionally, a buffer tank 5 is provided to stabilize the inlet pressure of the methanol supply device 9. Alternatively, the main on / off valve 7 can be used without employing it, and its function can be achieved by opening and closing a pump connected to the methanol fuel tank 3.

[0049] The methanol discharge system (MDS) comprises: an inactive gas storage tank 11 for storing inactive gas; an inactive gas supply unit 13 for supplying inactive gas from the inactive gas storage tank 11 to the internal combustion engine and the methanol supply device 9; a reflux chamber 15; a methanol discharge tank 17; and a pressure gauge PS (Pressure Sensor PS). Figure 2The pressure in the return chamber 15 is measured; the second valve group VT2, the third valve group VT3 and the fourth valve group VT4; and the valve controller VC ( Figure 2 It primarily controls the auxiliary on / off valves within the first to fourth valve groups VT1 to VT4 based on the output of the pressure gauge PS. It should be noted that in this embodiment, the valve controller VC also controls the on / off valve V0, which is included within the inactive gas supply unit 13 and controls the supply and cessation of the inactive gas.

[0050] like Figure 2 As shown, the second valve group VT2 includes a secondary on / off valve V2 and a check valve NRV2 arranged in series between the methanol supply device 9 and the return chamber 15. The third valve group VT3 includes secondary on / off valves V1 and V3, a check valve NRV1, and a remote operating valve PV arranged in series between the internal combustion engine 1 and the return chamber 15. After the methanol supply system MSS stops supplying methanol from the methanol fuel tank 3 to the internal combustion engine, when inactive gas is supplied from the inactive gas storage tank 11 to the internal combustion engine and the methanol supply system, the remote operating valve PV and the on / off valve V0 in the inactive gas supply section 13 open and close synchronously. Furthermore, the fourth valve group VT4 includes a secondary on / off valve V4, a pressure reducing valve RV1, and a check valve NRV3 arranged in series between the return chamber 15 and the methanol discharge tank 17.

[0051] In this embodiment, the pressure-reducing discharge mechanism RDM is configured to include: a pressure gauge PS that measures the pressure in the return chamber 15; a second valve group VT2 that has a secondary on / off valve V2 between the methanol supply device 9 and the return chamber 15; a third valve group VT3 that has a secondary on / off valve V3 between the internal combustion engine 1 and the return chamber 15; a fourth valve group VT4 that includes a secondary on / off valve V4 and a pressure-reducing valve RV1 between the return chamber 15 and the methanol discharge tank 17; and a valve controller VC that uses the output of the pressure gauge PS as part of the input to control the secondary on / off valves V2 to V4 in the first to fourth valve groups. The pressure-reducing discharge mechanism RDM discharges residual methanol and inactive gases from the return chamber 15 to the methanol discharge tank 17 at a pressure below a specified pressure. It should be noted that, in this embodiment, the valve controller VC stores the number of times (purification times) the inactive gas is supplied to the internal combustion engine 1 and the methanol supply system MSS via the inactive gas supply unit 13, such that the amount of residual methanol remaining in the internal combustion engine 1 and the methanol supply system MSS is less than a predetermined value (e.g., less than 1 μbar). This number can be predetermined by calculation based on the amount of inactive gas supplied in one operation and the internal volume of the gas flow path, so it is not necessary to detect residual methanol based on gas sensors or the like.

[0052] The amount of inactive gas supplied once from the inactive gas supply unit 13 is determined by the storage capacity of the reflux chamber 15. In this embodiment, the storage capacity of the reflux chamber 15 is determined by supplying inactive gas twice from the inactive gas supply unit 13, so that the amount of residual methanol remaining in the internal combustion engine 1 and the methanol supply system MSS is less than the aforementioned specified value. In this embodiment, the storage capacity of the reflux chamber 15 is less than 1 / 10 of the storage capacity of the methanol discharge tank 17.

[0053] The methanol discharge system MDS uses inert gas supplied from the inert gas supply unit 13 to the methanol supply system MSS to discharge residual methanol remaining in the internal combustion engine 1 and the methanol supply system MSS together with the inert gas into the methanol discharge tank 17. Here, after the methanol supply system MSS stops supplying methanol from the methanol fuel tank 3 to the internal combustion engine 1, the return chamber 15 temporarily stores the residual methanol discharged from the internal combustion engine 1 using the inert gas supplied from the inert gas supply unit 13 and the residual methanol discharged from the methanol supply device 9 in the methanol supply system MSS.

[0054] Furthermore, the pressure relief discharge mechanism RDM discharges residual methanol and inactive gases from the reflux chamber 15 to the methanol discharge tank 17 at a pressure below the specified pressure (1 bar). Figure 3 The operation flow of this embodiment is shown. Figure 3 In the operation process, in step ST1, the pressure reducing and exhaust mechanism RDM and the on / off valve V0 in the inactive gas supply section 13 simultaneously set the auxiliary on / off valve V2 of the second valve group VT2 and the auxiliary on / off valve V3 of the third valve group VT3 to the open state (at this time, the auxiliary on / off valve V1 and the remote operation valve PV are also in the open state), and set the auxiliary on / off valve V4 of the fourth valve group VT4 to the closed state, thereby starting a purification operation to discharge the residual methanol and inactive gas remaining in the internal combustion engine 1 and the methanol supply system MSS into the return chamber 15. In step ST1, the valve controller VC opens the on / off valves V0~V3 and closes the auxiliary on / off valve V4.

[0055] Then, in step ST2, the predetermined time period is confirmed to have ended. This predetermined time period is the time during which the inactive gas supply unit 13 ejects inactive gas once. When this time period ends, the inactive gas supply unit 13 stops ejecting a single amount of inactive gas. If the predetermined time period in step ST2 has ended, the process proceeds to step ST3, where it is confirmed that this is the nth time the inactive gas has been ejected [nth purification: i (number of purifications) < n (set number of times)], and the pressure in the return chamber 15 is determined.

[0056] Regardless of whether the pressure P in the reflux chamber 15 reaches 8 bar, when i=n, ​​proceed to step ST5 and close the on / off valves V0~V3, while in step ST6, the auxiliary on / off valve V4 opens. Then proceed to step ST7, where the pressure reducing and venting mechanism RDM discharges the residual methanol and inactive gases in the reflux chamber 15 to the methanol discharge tank 17 until the pressure P in the reflux chamber 15 becomes less than 1 bar (the third set value). When the pressure P in the reflux chamber 15 is less than 1 bar, the auxiliary on / off valve V4 closes and the purification operation ends (step 8).

[0057] When i < n, upon entering step ST3, if the pressure P in the reflux chamber 15 is above 8 bar (the first set value), then proceed to step ST9, where the opening and closing valves V0-V3 close and the auxiliary opening and closing valve V4 opens. Then proceed to step ST10, where the pressure-reducing discharge mechanism RDM discharges the residual methanol and inactive gases in the reflux chamber 15 to the methanol discharge tank 17 until the pressure P in the reflux chamber 15 becomes less than 1 bar (the second set value). When the pressure P in the reflux chamber 15 is less than 1 bar, proceed to step ST11, where the opening and closing valves V0-V3 open and the auxiliary opening and closing valve V4 closes, and proceed to step ST2. This discharge action is repeated until i = n. When i = n, the purification process ends at step ST5, proceeding from step ST3. It should be noted that, according to the above procedure, even if the pressure in the reflux chamber 15 does not reach the first set value (8 bar), the residual methanol and inactive gases in the reflux chamber 15 are still discharged to the methanol discharge tank 17.

[0058] It should be noted that, Figure 3 The operational process can be implemented using a computer-equipped processing unit. Such a processing unit can be installed within the valve controller VC.

[0059] According to this embodiment, residual methanol and inert gases are temporarily stored in the reflux chamber 15 and discharged from the reflux chamber 15 to the methanol discharge tank 17 at a pressure below a specified pressure (8 bar). Therefore, the methanol discharge tank 17 is filled with residual methanol and inert gases at a pressure below the specified pressure. As a result, according to this embodiment, it is not necessary to use expensive methanol discharge tanks with high pressure resistance as in the past, thereby significantly reducing equipment costs.

[0060] Industrial availability

[0061] According to the present invention, when inert gas is supplied to the internal combustion engine and the methanol supply system via the inert gas supply unit, the residual methanol remaining in the internal combustion engine and the methanol supply system is partially purified by the inert gas, and the purified residual methanol and inert gas are temporarily stored in the reflux chamber. Furthermore, a discharge operation is performed to discharge the residual methanol and inert gas temporarily stored in the reflux chamber to the methanol discharge tank at a pressure below a specified pressure. Therefore, it is unnecessary to use the expensive methanol discharge tank with high pressure resistance as in the past, thereby significantly reducing equipment costs.

Claims

1. A ship that uses methanol as fuel, characterized in that, The ship that uses methanol as fuel is equipped with a methanol supply system and a methanol discharge system. The methanol supply system includes: an internal combustion engine located in an engine room and capable of operating with methanol as fuel; and a methanol fuel tank for storing the methanol as fuel. And a methanol supply device that supplies methanol from the methanol fuel tank to the internal combustion engine. The methanol discharge system comprises: an inert gas storage tank for storing inert gas; an inert gas supply unit that, after the methanol supply system stops supplying methanol from the methanol fuel tank to the internal combustion engine, supplies a predetermined amount of the inert gas from the inert gas storage tank to the internal combustion engine and the methanol supply system; and a methanol discharge tank, wherein the methanol discharge system uses the inert gas supplied from the inert gas supply unit to the internal combustion engine and the methanol supply system to discharge residual methanol remaining in the internal combustion engine and the methanol supply unit, together with the inert gas, into the methanol discharge tank. The methanol discharge system comprises: a reflux chamber, which has a smaller capacity than the methanol discharge tank and temporarily stores the residual methanol and the inactive gas discharged from the internal combustion engine via the supply of the inactive gas from the inactive gas supply unit, as well as the residual methanol and the inactive gas discharged from the methanol supply device; and a pressure-reducing discharge mechanism that discharges the residual methanol and the inactive gas from the reflux chamber to the methanol discharge tank at a pressure below a predetermined pressure. When the methanol discharge system supplies the inert gas to the internal combustion engine and the methanol supply system through the inert gas supply section, it causes the discharge action of the pressure relief discharge mechanism to stop. When the methanol discharge system does not supply the inactive gas to the internal combustion engine and the methanol supply system through the inactive gas supply section, the pressure-reducing discharge mechanism is activated to discharge the gas in the return chamber to the methanol discharge tank at a pressure below the specified pressure. The methanol discharge system determines the number of times it supplies inert gas to the internal combustion engine and the methanol supply system via the inert gas supply unit, such that the amount of residual methanol remaining in the internal combustion engine and the methanol supply system is less than a predetermined value.

2. The ship using methanol as fuel according to claim 1, wherein, The inactive gas is supplied to the internal combustion engine and the methanol supply system more than twice via the inactive gas supply unit.

3. The ship using methanol as fuel according to claim 1, characterized in that, The methanol discharge system counts the number of times (i) the inactive gas is supplied to the internal combustion engine and the methanol supply system via the inactive gas supply unit. When the predetermined number n is reached, the methanol discharge system stops supplying the inactive gas to the internal combustion engine and the methanol supply system through the inactive gas supply unit. When the pressure in the reflux chamber drops to a predetermined pressure, the methanol discharge system stops discharging the residual methanol and the inactive gas from the reflux chamber to the methanol discharge tank. The methanol discharge system repeatedly performs the following actions: In the supply operation of supplying the inactive gas through the inactive gas supply unit, when the pressure of the gas in the return chamber reaches a predetermined first set value, the supply of the inactive gas to the internal combustion engine and the methanol supply system is stopped, and the pressure reducing and venting mechanism is activated to perform a venting operation to discharge the gas in the return chamber to the methanol discharge tank at a pressure below the predetermined pressure, until the number of times i reaches a predetermined number of times n; as well as When the pressure of the gas in the reflux chamber drops to a second set value that is lower than the first set value, the operation of the pressure relief and discharge mechanism is stopped, thus stopping the discharge operation.

4. The ship using methanol as fuel according to claim 1, wherein, The methanol supply system has the following features: A buffer tank is disposed between the methanol fuel tank and the methanol supply device and adjusts the pressure of the methanol supplied from the methanol fuel tank; The main on / off valve controls the supply and stoppage of methanol from the methanol fuel tank; as well as A first valve assembly is configured between the methanol supply device and the internal combustion engine to control the passage of the methanol, the residual methanol, and the inactive gas.

5. The ship using methanol as fuel according to claim 2, wherein, The pressure relief mechanism includes: A pressure gauge that measures the pressure within the reflux chamber; The second valve assembly has a secondary on / off valve between the methanol supply device and the reflux chamber; The third valve assembly has a secondary on / off valve between the internal combustion engine and the return chamber; The fourth valve assembly includes a secondary on / off valve and a pressure reducing valve between the reflux chamber and the methanol discharge tank; as well as A valve controller that uses the output of the pressure gauge as input to control the auxiliary on / off valves in the second to fourth valve groups.

6. The ship using methanol as fuel according to claim 2, wherein, The first setting is below 8 bar, and the second setting is below 1 bar.

7. The ship using methanol as fuel according to claim 1, wherein, The storage capacity of the reflux chamber is less than 1 / 10 of the capacity of the methanol discharge tank.

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