Ships that use methanol as fuel

Abstract

To provide a methanol-fueled vessel that does not incur increased equipment costs even with the addition of a methanol drain tank. [Solution] The methanol discharge system stops the discharge operation of the pressure-reducing discharge mechanism when inert gas is supplied to the internal combustion engine 1 and methanol supply system MSS through the inert gas supply unit 13. When inert gas is not supplied to the internal combustion engine 1 and methanol supply system MSS through the inert gas supply unit 13, the pressure-reducing discharge mechanism is activated to discharge the gas in the return chamber 15 to the methanol drain tank 17 at a pressure below a predetermined pressure. The number of times inert gas is supplied to the internal combustion engine and methanol supply system through the inert gas supply unit is determined so that the amount of residual methanol remaining in the internal combustion engine 1 and methanol supply system MSS is less than a predetermined value.

Description

Technical Field

[0001] The present invention relates to a ship using methanol as fuel.

Background Art

[0002] In FIG. 1 of Japanese Patent No. 6262076 (Patent Document 1), a conventional methanol-powered ship is disclosed, which includes a methanol discharge system for discharging methanol remaining in a methanol supply system that supplies methanol from a methanol fuel tank to an internal combustion engine when switching the fuel of the internal combustion engine. The conventional methanol-powered ship is arranged in the engine room and includes an internal combustion engine 11 that can operate using methanol as fuel, a methanol fuel tank 12 that stores methanol as fuel, a methanol supply system 13 that supplies methanol from the methanol fuel tank to the internal combustion engine, a valve unit 14 including a plurality of control valves for controlling the supply and supply amount of methanol supplied from the methanol fuel tank to the internal combustion engine, an inert gas generation system 15 that generates inert gas, and a methanol discharge system that discharges methanol remaining in the internal combustion engine 11 and the methanol supply system 13 into a methanol drain tank 16 through a discharge line. In the ship described in Patent Document 1, there is a problem that the discharged methanol cannot be reused. 12 From the methanol fuel tank to the internal combustion engine, it includes a valve unit 14 including a plurality of control valves for controlling the supply and supply amount of methanol supplied to the internal combustion engine, an inert gas generation system 15 that generates inert gas, and an inert gas (inert gas) is used to discharge the methanol remaining in the internal combustion engine 11 and the methanol supply system 13 through the discharge line. n24 It is provided with a methanol discharge system that discharges it into a methanol drain tank 16. In the ship described in Patent Document 1, there is a problem that the discharged methanol cannot be reused.

[0003] Therefore, as proposed in the fuel supply device shown in FIG. 1 of Japanese Patent No. 7357726 (Patent Document 2), it has been proposed to provide a service tank 4 between the fuel tank 2 and the fuel supply system. This service tank 4 mixes the fuel (methanol) sent from the fuel tank 2 through the fuel supply line and a part of the fuel returned from the internal combustion engine through the fuel return line, enabling the reuse of the purged fuel.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Patent No. 6262076 [Patent Document 2] Patent No. 7357726 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] If a service tank is provided, as in the fuel supply device shown in Figure 1 of Patent Document 2, it becomes necessary to secure a place to install the service tank, and the service tank will not only have the same installation requirements as a methanol fuel tank (such as the need for fire extinguishing equipment), but it will also be necessary to reinforce the service tank so that it can withstand the pressure of the inert gas (minimum 8 bar), which presents a problem.

[0006] Furthermore, as in the invention of Patent Document 1, residual methanol remaining in the methanol supply system 13 inert gas In a methanol discharge system that discharges methanol into a methanol drain tank 16 along with other substances, the methanol drain tank also needs to be pressure-resistant, which leads to increased equipment costs.

[0007] The objective of the present invention is to provide a methanol-fueled vessel that does not incur high equipment costs. [Means for solving the problem]

[0008] The methanol-fueled vessel of the present invention is equipped with a methanol supply system and a methanol discharge system. The methanol supply system includes an internal combustion engine located in the engine room and capable of operating on methanol as fuel, a methanol fuel tank for storing methanol as fuel, and a methanol supply device (LFSS) for supplying methanol from the methanol fuel tank to the internal combustion engine. The methanol discharge system includes an inert gas storage tank for storing inert gas, an inert gas supply unit that supplies (injects) inert gas from the inert gas storage tank to the internal combustion engine and methanol supply system after the methanol supply system has stopped supplying methanol from the methanol fuel tank to the internal combustion engine, and a methanol drain tank. The inert gas supplied from the inert gas supply unit to the internal combustion engine and methanol supply system is used to discharge residual methanol remaining in the internal combustion engine and methanol supply device (LFSS) together with the inert gas through a return chamber into the methanol drain tank.

[0009] The methanol discharge system used in the present invention is methanol drain tank The methanol discharge system includes a return chamber for temporarily storing residual methanol and inert gas discharged from the internal combustion engine and the methanol supply system (LFSS) in amounts less than the system's capacity, and a depressurized discharge mechanism for discharging residual methanol and inert gas from the return chamber to the methanol drain tank at a pressure below a predetermined pressure. The methanol discharge system stops the discharge operation of the depressurized discharge mechanism when inert gas is being supplied (injected) to the internal combustion engine and methanol supply system through the inert gas supply unit, and operates the depressurized discharge mechanism to discharge the gas in the return chamber to the methanol drain tank at a pressure below a predetermined pressure when inert gas is not being supplied to the internal combustion engine and methanol supply system through the inert gas supply unit. The methanol discharge system has a predetermined number of times in which inert gas is supplied to the internal combustion engine and methanol supply system through the inert gas supply unit so that the amount of residual methanol remaining in the internal combustion engine and methanol supply system is less than a predetermined value.

[0010] According to the present invention, when inert gas is supplied to the internal combustion engine and methanol supply system through an inert gas supply unit, residual methanol remaining in the internal combustion engine and methanol supply system is partially purged by the inert gas, and the purged residual methanol and inert gas are temporarily stored in a return chamber. Then, a discharge operation is performed to discharge the residual methanol and inert gas temporarily stored in the return chamber to a methanol drain tank at a pressure below a predetermined pressure. As a result, according to the present invention, it is not necessary to use a methanol drain tank that has high pressure resistance and is expensive, as in the conventional method, and equipment costs can be reduced significantly.

[0011] The number of times inert gas is supplied to the internal combustion engine and methanol supply system through the inert gas supply unit is two or more. The more times this is done, the smaller the methanol drain tank capacity can be.

[0012] The methanol discharge system has a function to count the number of times i inert gas is supplied to the internal combustion engine and methanol supply system through the inert gas supply unit. This function can be achieved by installing a counter that counts the number of times an on-off valve V0, located within the inert gas supply unit and on the outlet side of the inert gas storage tank, is opened or closed, or by counting the on-off commands supplied to the on-off valve V0. When the number i reaches a predetermined number n, the supply of inert gas to the internal combustion engine and methanol supply system through the inert gas supply unit is stopped, and the purge operation is turned off. Then, 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 drain tank is stopped.

[0013] Until the number of cycles i reaches a predetermined number of cycles n, when the gas pressure in the return chamber reaches a predetermined first set value while inert gas is being supplied (injected) through the inert gas supply unit, the supply of inert gas to the internal combustion engine and methanol supply system is stopped, and the pressure reduction discharge mechanism is activated to discharge the gas in the return chamber to the methanol drain tank at a pressure below a predetermined pressure. When the gas pressure in the return chamber drops to a second set value lower than the first set value, the operation of the pressure reduction discharge mechanism is stopped, and the discharge operation is stopped, and this process is repeated. return You may do so.

[0014] In a specific example, the methanol supply system may include a methanol supply device having the function of selectively supplying methanol supplied from a methanol fuel tank or inert gas supplied from an inert gas storage tank to an internal combustion engine, and supplying residual methanol to a return chamber; a buffer tank positioned between the methanol fuel tank and the methanol supply device to adjust the pressure of methanol supplied from the methanol fuel tank; a main shut-off valve V that controls the supply and cessation of methanol supplied from the methanol fuel tank; and a first valve train VT1 positioned between the methanol supply device and the internal combustion engine to control the passage of methanol, residual methanol, and inert gas. Of course, the function of a main shut-off valve may be achieved by switching a pump provided for the methanol fuel tank on and off instead of using a main shut-off valve. Furthermore, pressure adjustment may be performed using a valve train including a pressure reducing valve, etc., instead of using a buffer tank.

[0015] Furthermore, the methanol discharge system's pressure reduction discharge mechanism includes a pressure measuring instrument PS for measuring the pressure in the return chamber, a second valve train VT2 having a sub-on-off valve V2 between the methanol supply device and the return chamber, a third valve train VT3 having a sub-on-off valve V3 between the internal combustion engine and the return chamber, a fourth valve train VT4 including a sub-on-off valve V4 and a pressure reducing valve RV1 between the return chamber and the methanol drain tank, and the second valve train receiving the output of the pressure measuring instrument as input. first thingIt can be configured to include a valve controller that controls the sub - opening / closing valves V2 to V4 within the 4 - valve row. With such a configuration of the pressure - reducing discharge mechanism, the pressure - reducing discharge mechanism can be easily configured.

[0016] The third valve row VT3 preferably includes a remotely - operated valve PV that is opened when purging the inert gas. If the remotely - operated valve PV is provided in the third valve row VT3, purging can be surely carried out.

[0017] The values of the first set value and the second set value may be determined according to the design conditions, but it is preferable that the first set value is 8 bar or less and the second set value is 1 bar or less.

[0018] The storage capacity of the return chamber is preferably 1 / 10 or less of the capacity of the methanol drain tank. Under such conditions, it becomes possible to use the above - mentioned first set value and second set value.

Brief Description of the Drawings

[0019] [Figure 1] It is a block diagram of the main part of a fuel supply and discharge system that supplies fuel to and discharges fuel from an internal combustion engine of a ship using methanol as fuel in this embodiment. [Figure 2] It is a block diagram specifically showing each valve row included in FIG. 1. [Figure 3] It is a flowchart of the operation of the methanol discharge system.

Embodiments for Carrying Out the Invention

[0020] An example of an embodiment of the methanol-fueled vessel of the present invention will be described in detail below with reference to the drawings. Figure 1 is a block diagram of the main part of the fuel supply and discharge system that supplies fuel to and discharges fuel to the internal combustion engine of the methanol-fueled vessel of this embodiment. Figure 2 is a block diagram that specifically shows each valve row included in Figure 1. Figure 3 is a flowchart of the operation of the methanol discharge system. The fuel supply and discharge system of the methanol-fueled vessel of this embodiment is broadly divided into a methanol supply system MSS, which is located in the engine room and supplies methanol from a methanol fuel tank 3 to an internal combustion engine 1 that can operate on methanol as fuel, and a methanol discharge system MDS, which discharges (purges) methanol remaining in the methanol supply system MSS using an inert gas (nitrogen gas in this example) stored in an inert gas storage tank 11 when the fuel of the internal combustion engine 1 is switched.

[0021] The methanol supply system MSS is configured to control the supply and supply amount of methanol supplied from the methanol fuel tank 3 to the internal combustion engine 1. The methanol supply system MSS used in this embodiment includes a buffer tank 5, a main on-off valve 7, and a first valve train VT1. The buffer tank 5 is disposed between the methanol fuel tank 3 and the methanol supply device 9 to adjust the pressure of the methanol supplied from the methanol fuel tank 3. The main on-off valve 7 controls the supply and stop of the methanol supplied from the methanol fuel tank 3. The methanol supply device 9 has a function of supplying the methanol supplied from the methanol fuel tank 3 to the internal combustion engine 1 via the first valve train, and a function of supplying a part of the inert gas supplied from the inert gas storage tank 11 to the return chamber 15 described later together with the residual methanol via the second valve train VT2 during fuel switching. The first valve train VT1 includes a sub on-off valve for controlling the supply of methanol, and a sub on-off valve for controlling the discharge of a part of the inert gas supplied from the inert gas storage tank 11 and the residual methanol to the methanol supply device 9 during fuel switching. The first valve train VT1 has an arbitrary configuration including a sub on-off valve for controlling the discharge of a part of the inert gas supplied from the inert gas storage tank 11 and the residual methanol to the return chamber 15 via the internal combustion engine 1 during fuel switching.

[0022] During fuel switching of the internal combustion engine 1, the sub on-off valve in the first valve train VT1 closes to prevent methanol from being supplied to the internal combustion engine 1, and another sub on-off valve opens to allow the inert gas to be supplied to the internal combustion engine 1. The buffer tank 5 is provided for the purpose of stabilizing the inlet pressure of the methanol supply device 9. Of course, it is also possible to realize the role of the main on-off valve 7 by turning on and off a pump provided for the methanol fuel tank 3 without using the main on-off valve 7.

[0023] The methanol discharge system MDS comprises an inert gas storage tank 11 for storing inert gas, an inert gas supply unit 13 for supplying inert gas from the inert gas storage tank 11 to the internal combustion engine and methanol supply device 9, a return chamber 15, a methanol drain tank 17, a pressure measuring instrument PS (Figure 2) for measuring the pressure in the return chamber 15, a second valve train VT2, a third valve train VT3, and a fourth valve train VT4, and a valve controller VC (Figure 2) that primarily controls the sub-on-off valves in the first to fourth valve trains VT1 to VT4 based on the output of the pressure measuring instrument PS. In this embodiment, the valve controller VC is also included in the inert gas supply unit 13 and controls the on-off valve V0 that controls the supply and cessation of inert gas.

[0024] As shown in Figure 2, the second valve train VT2 has a secondary shut-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 train VT3 has secondary shut-off valves V1 and V3, a check valve NRV1 and a remote control valve PV arranged in series between the internal combustion engine 1 and the return chamber 15. The remote control valve PV supplies inert gas from the inert gas storage tank 11 after the methanol supply system MSS stops supplying methanol from the methanol fuel tank 3 to the internal combustion engine. Internal combustion engine Furthermore, when supplying methanol to the methanol supply system, it opens and closes in sync with the on-off valve V0 in the inert gas supply unit 13. The fourth valve row VT4 has a sub-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 drain tank 17.

[0025] In this embodiment, a pressure measuring instrument PS measures the pressure inside the return chamber 15, a second valve train VT2 having a sub-on-off valve V2 between the methanol supply device 9 and the return chamber 15, a third valve train VT3 having a sub-on-off valve V3 between the internal combustion engine 1 and the return chamber 15, a fourth valve train VT4 including a sub-on-off valve V4 and a pressure reducing valve RV1 between the return chamber 15 and the methanol drain tank 17, and the output of the pressure measuring instrument PS is used as a partial input to the first valve train first thingA valve controller VC controls the sub-on-off valves V2 to V4 in the 4-valve row, and a pressure-reducing discharge mechanism RDM is configured to discharge residual methanol and inert gas from the return chamber 15 to the methanol drain tank 17 at a pressure below a predetermined pressure. In this embodiment, the valve controller VC stores the number of times (purge count) that inert gas is supplied to the internal combustion engine 1 and the methanol supply system MSS through the inert 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 a predetermined value (e.g., 1 μbar or less). Since this count can be predetermined by calculation based on the amount of inert gas supplied in one instance and the volume of the gas flow path, there is no need to detect residual methanol using a gas sensor or the like.

[0026] The amount of inert gas supplied from the inert gas supply unit 13 in one go is determined by the storage capacity of the return chamber 15. In this embodiment, the storage capacity of the return chamber 15 is set such that the amount of residual methanol remaining in the internal combustion engine 1 and methanol supply system MSS is less than the predetermined value mentioned above, by supplying inert gas twice from the inert gas supply unit 13. In this embodiment, the storage capacity of the return chamber 15 is 1 / 10 or less of the storage capacity of the methanol drain tank 17.

[0027] 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 into the methanol drain tank 17 together with the inert gas. Here, the return chamber 15 temporarily stores the residual methanol discharged from the internal combustion engine 1 and the residual methanol discharged from the methanol supply device 9 in the methanol supply system MSS after the methanol supply system MSS stops supplying methanol from the methanol fuel tank 3 to the internal combustion engine 1, using the inert gas supplied from the inert gas supply unit 13.

[0028] And the vacuum discharge mechanism RDM discharges the residual methanol and inert gas from the return chamber 15 to the methanol drain tank 17 at a pressure of a predetermined pressure (1 bar) or less. Fig. 3 shows the operation flow of this embodiment. In the operation flow of Fig. 3, in step ST1, the vacuum discharge mechanism RDM opens the sub-opening / closing valve V2 of the second valve train VT2 and the sub-opening / closing valve V3 of the third valve train VT3 in synchronization with the opening / closing valve V0 in the inert gas supply section 13 (at this time, the sub-opening / closing valve V1 and the remote operation valve PV are also in the open state), and closes the sub-opening / closing valve V4 of the fourth valve train VT4, thereby starting a purge operation to discharge the residual methanol remaining in the internal combustion engine 1 and the methanol supply system MSS into the return chamber 15 together with the inert gas. The valve controller VC opens the opening / closing valves V0 to V3 in step ST1 , vice and closes the opening / closing valve V4.

[0029] Then, it is confirmed in step ST2 that the predetermined time period has ended. This predetermined time period is the time period during which the inert gas supply section 13 ejects the inert gas once. When this time period ends, the inert gas supply section 13 finishes ejecting the inert gas for one time. When the predetermined time period ends in step ST2, it proceeds to step ST3. In step ST3, it is confirmed which time the inert gas S ejection is (which purge is it: i (purge number) < n (set number)), and the pressure in the return chamber 15 is determined.

[0030] Regardless of whether the pressure P in the return chamber 15 has reached 8 bar, when i = n, it proceeds to step ST5, the opening / closing valves V0 to V3 are closed, and in step ST6 Deputy the opening / closing valve V4 is opened. Then it proceeds to step ST7, and the vacuum discharge mechanism RDM discharges the residual methanol and inert gas in the return chamber 15 to the methanol drain tank 17 until the pressure P in the return chamber 15 becomes less than 1 bar (the third set value). When the pressure P in the return chamber 15 becomes less than 1 bar Deputy the opening / closing valve V4 is closed and the purge operation ends (step ST 8).

[0031] When proceeding to step ST3 in the state of i < n, if the pressure P in the return chamber 15 is 8 bar (the first set value) or more, proceed to step ST9 , open The shut-off valves V0 to V3 are closed, Deputy The on-off valve V4 is opened. And proceed to step ST 10 Proceed to and the pressure reducing and discharging mechanism RDM discharges the residual methanol and inert gas in the return chamber 15 to the methanol drain tank 17 until the pressure P in the return chamber 15 becomes less than 1 bar (the second set value). When the pressure P in the return chamber 15 becomes less than 1 bar, proceed to step ST11, the on-off valves V0 to V3 are opened, Deputy The on-off valve V4 is closed, and proceed to step ST2. Thereafter, this discharging operation is repeated until i = n, and when i = n, proceed from step ST3 to step ST5 and the purge operation ends. According to the above operation flow, even when the pressure in the return chamber 15 does not reach the first set value (8 bar), the residual methanol and inert gas in the return chamber 15 are discharged to the methanol drain tank 17.

[0032] Note that the operation flow of FIG. 3 can be realized by using an arithmetic processing unit equipped with a computer. Such an arithmetic processing unit can be mounted in the valve controller VC.

[0033] According to the present embodiment, the residual methanol and inert gas are temporarily stored in the return chamber 15 and discharged from the return chamber 15 to the methanol drain tank 17 at a pressure of a predetermined pressure (8 bar) or less. Therefore, the methanol drain tank 17 is filled with the residual methanol and inert gas at a pressure of a predetermined pressure or less. As a result, according to the present embodiment, it is not necessary to use an expensive methanol drain tank having high pressure resistance as in the prior art, and the equipment cost can be significantly reduced.

Industrial Applicability

[0034] According to the present invention, when inert gas is supplied to the internal combustion engine and methanol supply system through the inert gas supply unit, residual methanol remaining in the internal combustion engine and methanol supply system is partially purged by the inert gas, and the purged residual methanol and inert gas are temporarily stored in the return chamber. Then, the residual methanol and inert gas temporarily stored in the return chamber are discharged to the methanol drain tank at a pressure below a predetermined pressure. As a result, there is no need to use a high-pressure-resistant and expensive methanol drain tank as in the conventional method, and equipment costs can be significantly reduced. [Explanation of Symbols]

[0035] 1. Internal combustion engine 3. Methanol fuel tank 5 Buffer Tank 7 Main valve 9. Methanol supply device 11. Inert gas storage tank 13. Inert gas supply unit 15. Return Chamber 17. Methanol drain tank MSS Methanol Supply System MDS Methanol Emission System RMD (Reduced Pressure Discharge Mechanism) VT1 First valve train VT2 Second valve train VT3 Third valve train VT4 4th valve train PS pressure measuring instrument VC valve controller

Claims

1. A methanol supply system comprising an internal combustion engine located in the engine room and capable of operating on methanol as fuel, a methanol fuel tank for storing the methanol as fuel, and a methanol supply device for supplying the methanol from the methanol fuel tank to the internal combustion engine, The system comprises an inert gas storage tank for storing inert gas, an inert gas supply unit that supplies a predetermined amount of the inert gas from the inert gas storage tank to the internal combustion engine and the methanol supply system after the methanol supply system has stopped supplying methanol from the methanol fuel tank to the internal combustion engine, and a methanol drain tank, and a methanol discharge system that 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 device into the methanol drain tank together with the inert gas. The methanol discharge system includes a return chamber that temporarily stores the residual methanol and inert gas discharged from the internal combustion engine and the residual methanol and inert gas discharged from the methanol supply device, with a capacity less than that of the methanol drain tank and supplied by the inert gas supply unit, and a depressurized discharge mechanism that discharges the residual methanol and inert gas from the return chamber to the methanol drain tank at a pressure below a predetermined pressure. The methanol discharge system is When the inert gas is supplied to the internal combustion engine and the methanol supply system through the inert gas supply unit, the discharge operation of the pressure reduction discharge mechanism is stopped. When the inert gas is not supplied to the internal combustion engine and the methanol supply system through the inert gas supply unit, the pressure reduction discharge mechanism is operated to discharge the gas in the return chamber to the methanol drain tank at a pressure below the predetermined pressure. A methanol-fueled vessel characterized in that the number of times the inert gas is supplied to the internal combustion engine and the methanol supply system through the inert gas supply unit is determined so 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 methanol-fueled vessel according to claim 1, wherein the number of times the inert gas is supplied to the internal combustion engine and the methanol supply system through the inert gas supply unit is two or more.

3. The methanol discharge system is The number of times i is supplied to the internal combustion engine and the methanol supply system through the inert gas supply unit is counted. When the number of times reaches a predetermined number n, the supply of the inert gas to the internal combustion engine and the methanol supply system through the inert gas supply unit is stopped. When the pressure in the return chamber drops to a predetermined pressure, the operation of discharging the residual methanol and the inert gas from the return chamber to the methanol drain tank is stopped. Until the number of times i reaches a predetermined number of times n, if the gas pressure in the return chamber reaches a predetermined first set value during the supply operation of the inert gas through the inert gas supply unit, the supply of the inert gas to the internal combustion engine and the methanol supply system is stopped, and the pressure reduction discharge mechanism is operated to discharge the gas in the return chamber to the methanol drain tank at a pressure below the predetermined pressure. A methanol-fueled vessel according to claim 1, characterized in that when the pressure of the gas in the return chamber falls to a second set value lower than the first set value, the operation of the decompression discharge mechanism is stopped and the discharge operation is stopped, and this operation is repeated.

4. The methanol supply system is A buffer tank is positioned between the methanol fuel tank and the methanol supply device to adjust the pressure of the methanol supplied from the methanol fuel tank. A main on / off valve V controls the supply and cessation of methanol supplied from the methanol fuel tank, A methanol-fueled vessel according to claim 1, comprising a first valve row disposed between the methanol supply device and the internal combustion engine for controlling the passage of methanol, residual methanol, and inert gas.

5. The aforementioned pressure reduction discharge mechanism is A pressure measuring instrument for measuring the pressure inside the return chamber, A second valve row having a secondary on / off valve is provided between the methanol supply device and the return chamber. A third valve row having a sub-on / off valve is provided between the internal combustion engine and the return chamber, A fourth valve row including a secondary shut-off valve and a pressure reducing valve is provided between the return chamber and the methanol drain tank. A methanol-fueled vessel according to claim 2, further comprising a valve controller that controls the auxiliary on-off valves in the second to fourth valve rows using the output of the pressure measuring instrument as input.

6. A methanol-fueled vessel according to claim 2, wherein the first setting value is 8 bar or less and the second setting value is 1 bar or less.

7. The methanol-fueled vessel according to claim 1, wherein the storage capacity of the return chamber is 1 / 10 or less of the capacity of the methanol drain tank.

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