Fuel supply system

Abstract

The fuel supply system according to the present invention comprises: a fuel tank in which a fuel gas is stored, the fuel tank being capable of accommodating a purge gas usable for a purge operation and a boil-off gas of the fuel gas; a fuel supply line for supplying fuel from the fuel tank to the engine; a purge gas generation unit for generating a purge gas suitable for a purge operation by using a mixed gas of a boil-off gas and a purge gas accommodated in the fuel tank; a purge line for purging the engine and the duct with the purge gas generated by the purge gas generation unit; and a recovery line connected to the purge line such that purge gas for the purge operation is recovered in the fuel tank.

Description

Technical Field

[0001] Cross-reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0129794, filed with the Korean Intellectual Property Office on September 26, 2023, under 35 USC §119, the entire contents of which are incorporated herein by reference.

[0003] This disclosure relates to a fuel supply system, and more specifically, to a fuel supply system designed to address the problems of toxic fuel gas emissions and purge gas loss through closed-loop purging of purge gas. Background Technology

[0004] In typical fuel systems, fuel used to power an engine can remain in the engine or piping. For example, when methanol is used as fuel, it is a low flash point fuel, so there is a risk of fire and explosion if methanol remains in the engine or piping. As another example, when ammonia is used as fuel, there is a risk of poisoning if ammonia leaks. Therefore, a fuel supply system should be installed to remove residual fuel from such engine systems.

[0005] Figure 1 This is a view of a fuel supply system (1) according to related technology. Typically, the fuel supply system is configured to use an inert gas, such as nitrogen, to purge and expel residual fuel inside the engine and piping. Fuel in the fuel tank (4) is supplied to the engine (2) via a fuel supply line (8) for power generation. When the engine stops and a purging operation is performed, purging gas is supplied via a purging gas supply line (6) to purge the engine (2) and piping. For reference, during the purging operation, a fuel shut-off valve (7) is closed, thereby preventing purging gas from flowing into the fuel supply line (8). The purging gas used in the purging operation flows into the fuel tank (4) along with residual fuel in the engine and piping via a fuel recovery line (3). Therefore, the pressure inside the fuel tank (4) increases, and to prevent overpressure (e.g., 0.2 bar), the fuel gas and purging gas in the fuel tank (4) are discharged into the atmosphere via a vent line (5).

[0006] Since the purging gas is discharged into the exhaust and consumed, new purging gas should be supplied again through the purging gas supply line (6) for the next purging operation, resulting in purging gas loss. Summary of the Invention

[0007] Technical issues

[0008] Therefore, this disclosure aims to solve the problems of fuel supply systems according to the related art, and to provide a fuel supply system that prevents the loss of purge gas by forming a closed loop, wherein the purge gas circulates within the fuel system.

[0009] Technical solution

[0010] A fuel supply system according to an embodiment of the present disclosure includes: a fuel tank storing fuel gas, the fuel tank being capable of containing purge gas for purging operations and evaporated fuel gas; a fuel supply line supplying fuel from the fuel tank to an engine; a purge gas generating unit utilizing a mixture of evaporated gas and purge gas contained in the fuel tank to generate purge gas suitable for purging operations; a purge line using the purge gas generated by the purge gas generating unit to purge the engine and pipes; and a recovery line connected to the purge line and recovering the purge gas used in the purging operations back to the fuel tank.

[0011] According to embodiments of this disclosure, the fuel supply system may include a supply valve disposed in a purge line and regulating the flow rate of purge gas.

[0012] According to embodiments of this disclosure, the fuel supply system may include a purge gas supply line connected to the fuel tank and supplying purge gas.

[0013] According to embodiments of the present disclosure, the fuel supply system may include a ventilation line connected to the fuel tank and discharging the mixed gas inside the fuel tank.

[0014] According to embodiments of the present disclosure, the purging gas generating unit may include: a compressor that compresses a mixed gas stored in a fuel tank; and a buffer tank disposed at the rear end of the compressor and temporarily storing the mixed gas compressed by the compressor.

[0015] According to embodiments of the present disclosure, the purging gas generating unit may include: a compressor that compresses a mixed gas stored in a fuel tank; and a purging gas purifier disposed at the rear end of the compressor and separating evaporated gas from the compressed mixed gas.

[0016] According to embodiments of this disclosure, the evaporated gas or liquid fuel separated by the purging gas purifier can be recovered to the fuel tank via an exhaust line.

[0017] According to embodiments of this disclosure, a purging gas purifier may include: an absorption purifier using an absorbent; a wastewater tank storing the absorbent used in the absorption purifier; and a degassing device separating the fuel absorbed in the absorbent in the wastewater tank.

[0018] According to embodiments of this disclosure, a purging gas purifier may include: an adsorption purifier using an adsorbent; and an adsorption supply valve disposed between the compressor and the adsorption purifier and regulating the supply pressure of the mixed gas to the adsorption purifier.

[0019] According to embodiments of this disclosure, a purging gas purifier may include: a heat exchanger that cools a mixed gas compressed by a compressor; and a gas-liquid separator disposed at the rear end of the heat exchanger and separating liquid fuel and purging gas from the mixed gas.

[0020] According to embodiments of this disclosure, the purging gas purifier may further include a buffer tank disposed at the rear end of the gas-liquid separator and temporarily storing the purging gas separated by the gas-liquid separator.

[0021] According to embodiments of this disclosure, in the recovery pipeline, residual fuel can be recovered together with the purging gas used in the purging operation.

[0022] According to embodiments of this disclosure, a pressure reducing valve can be installed in the recovery line to reduce the pressure of the purging gas used in the purging operation.

[0023] According to embodiments of this disclosure, the evaporating gas of the fuel gas may be methanol or ammonia, the purging gas may be nitrogen, and the purging gas may be a mixture of methanol or ammonia and nitrogen, or the purging gas may be nitrogen.

[0024] A fuel supply system according to another embodiment of the present disclosure includes: a fuel tank storing fuel gas, the fuel tank being capable of containing purge gas for purging operations and evaporated fuel gas; a fuel supply line supplying fuel from the fuel tank to an engine; a purge gas generating unit utilizing a mixture of evaporated gas and purge gas contained in the fuel tank to generate purge gas suitable for purging operations; an exhaust line recovering evaporated gas or liquid fuel separated by the purge gas generating unit back to the fuel tank; a purge line using the purge gas generated by the purge gas generating unit to purge the engine and pipes; and a recovery line connected to the purge line and recovering the purge gas used in the purging operations back to the fuel tank.

[0025] Beneficial effects

[0026] According to this disclosure, since the purging gas flows along a closed loop circulating within the fuel system, the purging operation can be performed without purging gas loss.

[0027] According to this disclosure, since it is not necessary to resupply purge gas, the problem of excessive pressure increase inside the fuel tank due to continuous purge gas supply, which in turn leads to frequent venting of toxic fuel gases along with the purge gas, can be solved. Attached Figure Description

[0028] Figure 1 It is a view of the fuel supply system based on relevant technologies.

[0029] Figure 2 A fuel supply system according to this disclosure is shown.

[0030] Figure 3 A fuel supply system for a purge gas generating unit according to a first embodiment of the present disclosure is shown.

[0031] Figure 4 A fuel supply system for a purge gas generating unit according to the (2-1) embodiment of the present disclosure is shown.

[0032] Figure 5 A fuel supply system for a purge gas generating unit according to the second (2-2) embodiment of the present disclosure is shown.

[0033] Figure 6 A fuel supply system for a purge gas generating unit according to embodiments (2-3) of this disclosure is shown. Detailed Implementation

[0034] In the following, some embodiments of the present disclosure will be described in detail with reference to the exemplary accompanying drawings. When adding reference numerals to components in each drawing, it should be noted that even if the same or equivalent components are shown in other drawings, these components are indicated by the same numerals. Furthermore, in describing embodiments of the present disclosure, detailed descriptions of related known configurations or functions will be omitted if it is determined that such detailed descriptions would interfere with the understanding of the embodiments of the present disclosure.

[0035] Furthermore, in the description of components in the embodiments of this disclosure, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended only to distinguish one component from other components, and they do not limit the nature, order, or sequence of the components. It should be understood that when one component is “connected,” “coupled,” or “engaged” to another component, the former may be directly connected or engaged to the latter, or may be “connected,” “coupled,” or “engaged” to the latter through a third component inserted between the two.

[0036] In this specification, for ease of description, the front-back direction, left-right direction, and up-down direction are mentioned, and these directions can be perpendicular to each other. However, these directions are determined relative to the orientation of the gas cutting device, and the up-down direction does not necessarily mean the vertical direction.

[0037] refer to Figure 1 This document describes a fuel supply system 100 according to an embodiment of the present disclosure. The fuel supply system 100 includes: a fuel tank 10 in which fuel gas is stored, the fuel tank 10 being capable of containing evaporated fuel gas and purge gas suitable for purging operations; a fuel supply line 340 for supplying fuel from the fuel tank 10 to an engine; a purge gas generating unit 200 that utilizes the evaporated gas and purge gas contained in the fuel tank 10 to generate purge gas suitable for purging operations; a purge line 310 that uses the purge gas generated by the purge gas generating unit 200 to purge the engine and pipes; and a recovery line 320 connected to the purge line 310 and recovering the purge gas used in the purging operation back to the fuel tank 10.

[0038] Fuel gas can be used as a term to encompass all gaseous fuels that are typically stored in a liquid state, such as liquefied petroleum gas (LPG), ethylene, ammonia, methanol, and hydrogen, and for convenience, fuels that are not in a liquid state due to heating or pressurization can also be referred to as fuel gas. The same applies to evaporating gases.

[0039] Inert gases such as nitrogen or argon can be used as purge gases, but this disclosure is not limited thereto. The term "purge gas" is used in this specification to distinguish it from "purge gas". "Purge gas" refers to the gas actually used in the purging operation, which is generated by the purge gas generating unit 200 and flows along the purge line 310. The purge gas can be a mixture of evaporating gas and purge gas, or it can be a pure purge gas. This can vary depending on the processing method of the purge gas generating unit 200, which will be described below.

[0040] Fuel gas can be stored in fuel tank 10, and purge gas and fuel gas vapors used for purging operations can be contained together in the upper part of the fuel tank. A purge gas supply line 330 can be connected to fuel tank 10 to supply purge gas to fuel tank 10. This purge gas can also be used to prevent pressure drop inside fuel tank 10. A regulator 12 for adjusting the flow rate of the purge gas can be provided in the purge gas supply line 330. When the amount of purge gas used to maintain the pressure of fuel tank 10 is insufficient, the regulator 12 can automatically open to supply additional purge gas through the purge gas supply line 330 to prevent structural damage to fuel tank 10.

[0041] In the purging system according to this disclosure, a closed loop of purging gas is configured so that once purging gas is supplied to the fuel tank 10 through the purging gas supply line 330, no subsequent resupply of purging gas is required.

[0042] Furthermore, since there is no need to resupply purge gas, the problem of excessive pressure increase inside the fuel tank 10 due to continuous purge gas supply, which would require frequent venting of toxic fuel gases (e.g., methanol or ammonia) along with the purge gas, can be solved.

[0043] The purging gas generating unit 200 utilizes the mixed gas inside the fuel tank 10 to generate purging gas suitable for purging operations. Liquefied fuel or evaporated gas separated by the purging gas generating unit 200 can be recovered to the fuel tank 10 via the discharge line 350. Detailed configuration of the purging gas generating unit 200 will be provided in [reference needed]. Figures 3 to 6 Detailed description.

[0044] The engine and pipes are purged using purging gas generated by the purging gas generating unit 200. According to... Figure 2 The purge line 310 is shown as a line extending from the pipe connected to the purge gas generating unit 200 and passing through a portion of the fuel supply line 340 and the interior of the engine 20, but the purge line 310 can also be understood as a line circulating through the equipment and pipes required for the purge operation. A supply valve 30 may be provided in the purge line 310 to regulate the flow rate of the purge gas.

[0045] according to Figure 2 A heat exchanger 16 and a fuel shut-off valve 18 are shown in the fuel supply line 340, but these components can be replaced with other parts depending on the fuel system. A fuel discharge line 332 for discharging fuel when the engine is stopped can be provided in the fuel supply line 340.

[0046] Ventilation line 360 ​​can be connected to fuel tank 10 to vent the gas mixture inside fuel tank 10. Pressure relief valve 14 can be provided in ventilation line 360, thus preventing overpressure inside fuel tank 10.

[0047] The recovery line 320 is connected to the purge line 310 and recovers the purge gas used in the purge operation to the fuel tank 10. In the recovery line 320, residual fuel can be recovered along with the purge gas used in the purge operation. Therefore, the purge gas flows along the fuel tank 10, the purge gas generation unit 200, the purge line 310, and the recovery line 320, and is then recovered back to the fuel tank 10. Figure 2 The closed-loop flow of the purge gas is shown. Because the purge gas flows along the closed loop, the purging operation can be performed without purge gas loss (through reuse). A pressure reducing valve 50 for reducing the pressure of the purge gas used in the purging operation can be installed in the recovery line 320.

[0048] <First Embodiment>

[0049] Figure 3 A purging gas generating unit 200 according to a first embodiment is shown. The purging gas generating unit 200 may include: a compressor 210 that compresses a mixed gas stored in a fuel tank; and a buffer tank 220 disposed at the rear end of the compressor 210 and temporarily storing the mixed gas compressed by the compressor 210.

[0050] Compressor 210 compresses the mixture of evaporating gas and purge gas. The high-pressure mixture can be used as a purge gas, flowing along purge line 310 and recovery line 320, and then recovered back to fuel tank 10. The high-pressure mixture may contain a portion of the evaporating gas from the fuel gas, but when the mixing ratio is below the permissible reference value (e.g., 5% or less in the case of methanol), the purging operation can be performed even using a mixture containing the evaporating gas from the fuel gas.

[0051] Buffer tank 220 is used to temporarily store high-pressure purging gas. The amount of purging gas used in the purging operation is small compared to the total amount of purging gas contained in fuel tank 10, so the purging gas can be adequately contained in buffer tank 220. The mass of purging gas that can be contained in fuel tank 10 (e.g., at least 440 kg) is four times or more the mass of purging gas used for a single purging operation (e.g., up to 110 kg). In related art, purging gas (e.g., 110 kg) is supplied via purging gas supply line 330 each time a purging operation is performed. However, in this embodiment, the purging gas can be supplied to fuel tank 10 once via purging gas supply line 330, and then stored in buffer tank 220 for purging. Thereafter, the purging gas recovered to fuel tank 10 and stored in buffer tank 220 can be recycled. Values ​​such as 440 kg and 110 kg are exemplary, and this disclosure is not limited thereto.

[0052] Because the high-pressure purging gas is temporarily stored in the buffer tank 220, the capacity of the compressor 210 can be reduced. In other words, the high-pressure purging gas is pre-stored in the buffer tank 220, and during the purging operation, the compressor 210 additionally generates high-pressure purging gas, which is then discharged along with the gas. Therefore, the buffer tank 220 is provided to maintain sufficient purging gas pressure even when the compressor capacity is reduced.

[0053] When compressor 210 runs for an extended period, a large amount of gas inside fuel tank 10 is stored in buffer tank 220, reducing the amount of gas inside fuel tank 10 and thus lowering its pressure. Conversely, when compressor 210 runs for a short period, a small amount of gas inside fuel tank 10 is stored in buffer tank 220, and the amount of gas inside fuel tank 10 does not change significantly, thus maintaining the pressure of fuel tank 10. Therefore, the pressure inside fuel tank 10 can be regulated by adjusting the operation of compressor 210.

[0054] <Second Embodiment>

[0055] Figures 4 to 6 A purge gas generating unit 200 according to a second embodiment is shown. The purge gas generating unit 200 includes: a compressor 210 that compresses a mixed gas stored in a fuel tank 10; and a purge gas purifier 230 disposed at the rear end of the compressor 210 and separating evaporated gas from the compressed mixed gas. The separation of evaporated gas by the purge gas purifier 230 can improve the purity of the purge gas, thereby meeting permissible reference values ​​for purge gas (e.g., 5% or less in the case of methanol). The high-purity purge gas passing through the purge gas purifier 230 flows along a purge line 310 and a recovery line 320, and is then recovered back to the fuel tank 10.

[0056] Depending on the specific purification method, the purging gas purifier 230 is divided into the (2-1) embodiment (absorption purifier), the (2-2) embodiment (adsorption purifier), and the (2-3) embodiment (gas-liquid separator).

[0057] <Example (2-1)>

[0058] Reference Figure 4 The purging gas purifier 230 may include an absorption purifier 240 using an absorbent. For example, when the vaporized fuel gas is methanol or ammonia and the purging gas is nitrogen, a high-purity nitrogen gas can be generated using an absorbent. The absorbent used in the absorption purifier 240 is stored in a wastewater tank 242. To recover the absorbed fuel, a degassing device 244 can be used, which separates the fuel by heating the absorbent in the wastewater tank 242. Furthermore, the absorbent inside the wastewater tank 242 can be supplied to the absorption purifier 240 using an absorbent pump 246. The separated vaporized gas can be recovered to the fuel tank 10 through a discharge line 350. A discharge valve 40 may be installed in the discharge line 350.

[0059] The purge gas purifier 230 according to embodiment (2-1) may further include a buffer tank 264, which is disposed at the rear end of the absorption purifier 240 and temporarily stores the high-purity purge gas separated by the absorption purifier 240. Since the buffer tank 264 performs the same function as the buffer tank 220, a detailed description of the buffer tank 264 will be omitted.

[0060] <Example (2-2)>

[0061] Reference Figure 5 The purge gas purifier 230 may include an adsorption purifier 250 that uses an adsorbent. For example, when the vaporized fuel gas is methanol or ammonia and the purge gas is nitrogen, an adsorbent can be used to produce high-purity nitrogen. An adsorption supply valve 252 for regulating the supply pressure of the mixed gas to the adsorption purifier 250 may be provided between the compressor 210 and the adsorption purifier 250.

[0062] When compressor 210 is running, adsorption supply valve 252 is open, and supply valve 30 and discharge valve 40 are closed, creating a high-pressure environment inside adsorption purifier 250. Conversely, when compressor 210 stops, adsorption supply valve 252 is closed, and either supply valve 30 or discharge valve 40 is open, creating a low-pressure environment inside adsorption purifier 250. When this low-pressure environment is established, the evaporated gas can be desorbed from the adsorbent. The desorbed evaporated gas can be recovered to fuel tank 10 through discharge line 350. Discharge valve 40 can be installed in discharge line 350.

[0063] The purging gas purifier 230 according to embodiment (2-2) may further include a buffer tank 264, which is disposed at the rear end of the adsorption purifier 250 and temporarily stores the high-purity purging gas separated by the adsorption purifier 250. Since the buffer tank 264 performs the same function as the buffer tank 220, a detailed description of the buffer tank 264 will be omitted.

[0064] <Example (2-3)>

[0065] Reference Figure 6 The purging gas purifier 230 may include: a heat exchanger 262 that cools the mixed gas compressed by the compressor 210; and a gas-liquid separator 260 disposed at the rear end of the heat exchanger 262 and separating liquid fuel and purging gas from the mixed gas.

[0066] When the mixed gas is compressed by compressor 210, it forms a high-temperature, high-pressure mixed gas. When the high-temperature, high-pressure mixed gas is cooled by heat exchanger 262, the mixed gas is transformed into a low-temperature, high-pressure state, thus the evaporated gas is condensed into liquid fuel. The liquid fuel is collected in the lower part of gas-liquid separator 260, and the high-purity purge gas is collected in the upper part of gas-liquid separator 260, thereby separating the liquid fuel and the purge gas.

[0067] The purging gas purifier 230 according to embodiments (2-3) may further include a buffer tank 264, which is disposed at the rear end of the gas-liquid separator 260 and temporarily stores the high-purity purging gas separated by the gas-liquid separator 260. Since the buffer tank 264 performs the same function as the buffer tank 220, a detailed description of the buffer tank 264 will be omitted.

[0068] The above description is merely an illustration of the technical concept of this disclosure, and those skilled in the art can make various modifications and variations without departing from the basic characteristics of this disclosure. Therefore, the embodiments disclosed herein are not intended to limit the technical concept of this disclosure, but rather to describe it, and the scope of the technical concept of this disclosure is not limited by these embodiments. The scope of protection of this disclosure should be interpreted by the appended claims, and all technical concepts within the same scope should be interpreted as including within the scope of this disclosure.

[0069] List of reference numerals

[0070] 100: Fuel Supply System

[0071] 10: Fuel tank 20: Engine

[0072] 30: Supply valve 40: Discharge valve

[0073] 200: Purging gas generation unit

[0074] 210: Compressor 220: Buffer tank

[0075] 230: Purge gas purifier; 240: Absorption purifier.

[0076] 242: Wastewater tank; 244: Degassing device

[0077] 246: Absorbent pump; 250: Adsorption purifier

[0078] 252: Adsorption supply valve; 260: Gas-liquid separator

[0079] 262: Heat exchanger 264: Buffer tank

[0080] 310: Purge line; 320: Recovery line

[0081] 330: Purge gas supply line

[0082] 332: Fuel emission line

[0083] 340: Fuel supply line; 350: Emission line

[0084] 360: Ventilation ducts

Claims

1. A fuel supply system, comprising: A fuel tank containing fuel gas, the fuel tank being capable of holding purge gas for purging operations and evaporated fuel gas; A fuel supply line configured to supply fuel from the fuel tank to the engine; A purging gas generating unit is configured to generate purging gas suitable for the purging operation using a mixture of evaporated gas and purging gas contained in the fuel tank. A purging line configured to purge the engine and pipelines using purging gas generated by the purging gas generating unit; and A recovery line is connected to the purging line and configured to recover the purging gas used in the purging operation to the fuel tank.

2. The fuel supply system according to claim 1, comprising: A supply valve is provided in the purging line and configured to regulate the flow rate of the purging gas.

3. The fuel supply system according to claim 1, comprising: A purge gas supply line is connected to the fuel tank and configured to supply the purge gas.

4. The fuel supply system according to claim 1, comprising: A ventilation duct that is connected to the fuel tank and configured to discharge the mixed gas inside the fuel tank.

5. The fuel supply system according to claim 1, wherein The purging gas generating unit includes: A compressor configured to compress the gas mixture stored in the fuel tank; and A buffer tank is located at the rear end of the compressor and configured to temporarily store the mixed gas compressed by the compressor.

6. The fuel supply system according to claim 1, wherein The purging gas generating unit includes: A compressor configured to compress the gas mixture stored in the fuel tank; and A purging gas purifier is disposed at the rear end of the compressor and configured to separate the evaporated gas from the compressed gas mixture.

7. The fuel supply system according to claim 6, wherein The evaporated gas or liquid fuel separated by the purging gas purifier is recovered to the fuel tank through the discharge pipeline.

8. The fuel supply system according to claim 6, wherein The purging gas purifier includes: Absorption purifiers that use absorbents; Wastewater tank, configured to store the absorbent used in the absorption purifier; and A degassing device configured to separate fuel absorbed in the absorbent in the wastewater tank.

9. The fuel supply system according to claim 8, wherein The purging gas purifier also includes: A buffer tank is located at the rear end of the absorption purifier and configured to temporarily store the purge gas purified by the absorption purifier.

10. The fuel supply system according to claim 6, wherein, The purging gas purifier includes: Adsorption-type air purifiers that use adsorbents; and An adsorption supply valve is disposed between the compressor and the adsorption purifier and configured to regulate the supply pressure of the mixed gas to the adsorption purifier.

11. The fuel supply system according to claim 10, wherein, The purging gas purifier also includes: A buffer tank is located at the rear end of the adsorption purifier and configured to temporarily store the purging gas purified by the adsorption purifier.

12. The fuel supply system according to claim 6, wherein, The purging gas purifier includes: A heat exchanger configured to cool the mixed gas compressed by the compressor; and A gas-liquid separator is disposed at the rear end of the heat exchanger and configured to separate liquid fuel and purging gas from the mixed gas.

13. The fuel supply system according to claim 12, wherein, The purging gas purifier also includes: A buffer tank is located at the rear end of the gas-liquid separator and configured to temporarily store the purging gas separated by the gas-liquid separator.

14. The fuel supply system according to claim 1, wherein, A pressure reducing valve is provided in the recovery pipeline, the pressure reducing valve being configured to reduce the pressure of the purging gas used in the purging operation.

15. A fuel supply system, comprising: A fuel tank containing fuel gas, the fuel tank being capable of holding purge gas for purging operations and evaporated fuel gas; A fuel supply line configured to supply fuel from the fuel tank to the engine; A purging gas generating unit is configured to generate purging gas suitable for the purging operation using a mixture of evaporated gas and purging gas contained in the fuel tank. The discharge pipeline is configured to recover the evaporated gas or liquid fuel separated by the purge gas generating unit back to the fuel tank; A purging line configured to purge the engine and pipelines using purging gas generated by the purging gas generating unit; and A recovery line is connected to the purging line and configured to recover the purging gas used in the purging operation to the fuel tank.

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