Leak detection system for marine reliquefaction systems

Abstract

A leak detection system for a ship reliquefaction system is disclosed. The leak detection system of the present invention includes a gas supply line that supplies evaporated gas generated from liquefied gas stored in a storage tank to a compressor, a reliquefaction line that cools the compressed gas compressed by the compressor in a heat exchanger to reliquefy it and return it to the storage tank, a refrigerant circulation line in which a refrigerant that cools the compressed gas in the heat exchanger circulates, a refrigerant compressor that compresses the refrigerant discharged from the heat exchanger after cooling the compressed gas in the heat exchanger, a refrigerant expander that expands and cools the refrigerant compressed by the refrigerant compressor and then supplied to the heat exchanger and supplies it to the heat exchanger as a refrigerant, and a refrigerant filling line that connects an inventory tank filled with nitrogen gas and the upstream side of the refrigerant compressor of the refrigerant circulation line. At the initial start or restart of the reliquefaction process, nitrogen gas is supplied from the refrigerant filling line to the upstream side of the refrigerant compressor of the refrigerant circulation line to check for the presence or absence of a leak in the refrigerant circulation line.

Description

[Technical Field]

[0001] The present invention relates to a leak detection system for a reliquefaction system for a ship, and more particularly to a reliquefaction system that reliquefies evaporated gas generated in a storage tank installed on a ship, and to a leak detection system that detects leakage of a refrigerant or the like from a heat exchanger during initial startup or restart of the reliquefaction system. [Background technology]

[0002] Natural gas, primarily composed of methane, emits almost no environmental pollutants when burned, and is therefore gaining attention as an environmentally friendly fuel. Liquefied natural gas (LNG) is obtained by liquefying natural gas by cooling it to approximately -163°C at atmospheric pressure. LNG occupies approximately 1 / 600 of the volume of natural gas in its gaseous state, making it highly suitable for long-distance transportation via sea routes. For this reason, natural gas is primarily stored and transported in the liquid form of LNG, which is advantageous for storage and transportation.

[0003] Because the liquefaction point of natural gas is an extremely low temperature of approximately -163°C at normal pressure, LNG storage tanks are usually insulated to maintain the LNG in a liquid state. However, even with insulation, it is difficult to completely block external heat. Therefore, as external heat continues to be transferred to the LNG storage tank, the LNG in the LNG storage tank naturally vaporizes during the LNG transportation process, generating boil-off gas (BOG).

[0004] If evaporation continues to occur in an LNG storage tank, the pressure inside the tank will rise. If the pressure inside the storage tank exceeds the set safety pressure, an emergency such as tank rupture may occur, so it is necessary to use a safety valve to release the evaporation outside the storage tank. However, since evaporation is one type of LNG loss and is a significant issue in terms of LNG transportation efficiency and fuel efficiency, various methods are used to deal with evaporation generated in storage tanks.

[0005] In recent years, methods have been developed and are being used, such as using evaporated gas at fuel demand points such as ship engines, re-liquefying evaporated gas and recovering it in storage tanks, or combining these two methods. Summary of the Invention [Problem to be solved by the invention]

[0006] When applying a reliquefaction cycle to a ship to reliquefy evaporated gas, typical reliquefaction cycles include the SMR cycle and the C3MR cycle. The C3MR cycle (Propane-precooled Mixed Refrigerant Cycle) uses a single refrigerant, propane, to cool the evaporated gas, and then cools it again using a mixed refrigerant to reliquefy it. The SMR cycle (Single Mixed Refrigerant Cycle) uses a mixed refrigerant composed of multiple components to reliquefy the evaporated gas.

[0007] These SMR and C3MR cycles use a mixed refrigerant, and as the liquefaction process progresses, the refrigerant leaks. This causes the composition ratio of the mixed refrigerant to change, reducing the liquefaction efficiency. Therefore, it is necessary to continuously measure the composition ratio of the mixed refrigerant and replenish any missing refrigerant components to maintain the refrigerant composition.

[0008] Another known reliquefaction method that utilizes a reliquefaction cycle is a single-cycle reliquefaction method that uses nitrogen refrigerant.

[0009] Nitrogen refrigerants have a lower cooling efficiency than refrigeration cycles that use mixed refrigerants. However, because nitrogen refrigerants are an inert substance, they are highly safe, and because the refrigerant does not undergo phase change, they have the advantage of being easily applicable to ships.

[0010] The reliquefaction system includes a compressor that compresses the evaporated gas, a heat exchanger that cools the compressed gas compressed by the compressor by heat exchange with a refrigerant, and a refrigerant circulation unit in which the refrigerant used for heat exchange with the compressed gas in the heat exchanger circulates. In the case of a reliquefaction system that utilizes a refrigeration cycle using a nitrogen refrigerant, the nitrogen refrigerant discharged from the heat exchanger after heat exchange in the refrigerant circulation unit is compressed, supplied to the heat exchanger and cooled, further cooled by expansion, and then supplied to the heat exchanger again, thereby circulating the nitrogen refrigerant.

[0011] In this way, the reliquefaction system, particularly the heat exchanger, is supplied with cryogenic evaporated gas (LNG) or nitrogen refrigerant, which is colder than the evaporated gas. However, if damage to the heat exchanger causes a leak of cryogenic flammable material, this could pose a serious risk to the safety of the crew and the ship.

[0012] While the reliquefaction system is in operation, warning signals from pressure sensors installed upstream and downstream of each line connected to the heat exchanger immediately confirm any leaks of refrigerant, flammable materials, etc. However, when the reliquefaction system is initially started up or restarted after being stopped, the pressure sensors cannot detect leaks of refrigerant, etc., and if there is no device or indicator that can independently check for leaks, there is a problem that the discovery of leaks is delayed.

[0013] The present invention solves these problems and proposes a method for quickly checking for leaks of refrigerant or the like from a heat exchanger, even during initial start-up or restart of a reliquefaction system, thereby ensuring the safety of the ship. [Means for solving the problem]

[0014] In order to solve the above problem, an embodiment of the present invention includes a gas supply line that supplies evaporated gas generated from liquefied gas stored in a storage tank of a ship to a compressor; a re-liquefaction line that cools the compressed gas obtained by compressing the evaporated gas in the compressor in a heat exchanger to re-liquefy the compressed gas and returns it to the storage tank; a refrigerant circulation line that circulates a refrigerant that cools the compressed gas in the heat exchanger; a refrigerant compressor that is provided in the refrigerant circulation line and compresses the refrigerant discharged from the heat exchanger after cooling the compressed gas in the heat exchanger; and a refrigerant compressor that compresses the refrigerant after being compressed in the refrigerant compressor. and a refrigerant filling line connecting an inventory tank filled with nitrogen gas to the refrigerant circulation line upstream of the refrigerant compressor, wherein at the initial start or restart of the reliquefaction process, nitrogen gas is supplied from the refrigerant filling line to the refrigerant circulation line upstream of the refrigerant compressor, to check for the presence or absence of a leak in the refrigerant circulation line.

[0015] Preferably, the refrigerant circulation system further includes a first valve provided upstream of a connection point between the refrigerant circulation line and the refrigerant charging line, a second valve provided upstream of the first valve in the refrigerant circulation line between the refrigerant expander and the heat exchanger, and a third valve provided in the refrigerant charging line.

[0016] Preferably, the first and second valves are closed, the third valve is opened, nitrogen gas is supplied to the refrigerant circulation line, and it is confirmed whether there is any leakage in the portion of the refrigerant circulation line from the low-pressure portion upstream of the refrigerant compressor to the low-pressure portion downstream of the refrigerant expander. Then, the first and second valves are opened to fill the refrigerant circulation line with nitrogen refrigerant, and it is confirmed whether there is any leakage in the portion of the refrigerant circulation line from the low-pressure portion downstream of the refrigerant expander to the low-pressure portion upstream of the refrigerant compressor.

[0017] Preferably, the gas supply line is connected to the compressor via the heat exchanger and further comprises a fourth valve provided upstream of the heat exchanger on the gas supply line, and a fifth valve provided between the heat exchanger and the compressor on the gas supply line; and at the initial start or restart of the reliquefaction process, the fourth and fifth valves are closed to check for leaks in the low-pressure section of the heat exchanger through which the evaporated gas passes via the gas supply line, in parallel with checking for leaks in the refrigerant circulation line.

[0018] Preferably, the system further comprises a preheating line branching off from the gas supply line upstream of the fourth valve on the gas supply line and connected between the fourth valve and the heat exchanger on the gas supply line, a preheater provided in the preheating line and heating the evaporated gas passing through the preheating line, a sixth valve provided in the preheating line downstream of the preheater, and a seventh valve provided in a line branching off from the preheating line between the preheater and the sixth valve, bypassing the heat exchanger and connected to the gas supply line upstream of the compressor.

[0019] Preferably, the system further comprises a gas-liquid separator provided downstream of the heat exchanger on the reliquefaction line for separating the reliquefied gas into gas and liquid, a bypass line branching off from the reliquefaction line downstream of the heat exchanger and connecting to a storage tank, bypassing the gas-liquid separator, an eighth valve provided upstream of the heat exchanger on the reliquefaction line, a ninth valve provided on the reliquefaction line between the branching point of the bypass line and the gas-liquid separator, and a tenth valve provided on the bypass line, and at the initial start or restart of the reliquefaction process, the eighth to tenth valves are closed to check for leaks in the refrigerant circulation line and, in parallel with checking for leaks in the refrigerant circulation line, check for leaks in the high-pressure section of the heat exchanger through which the compressed gas passes via the reliquefaction line.

[0020] Preferably, the system further comprises a pressure compensation line branching off from the reliquefaction line between the compressor and the heat exchanger of the reliquefaction line and connected to an upper part of the gas-liquid separator, a nitrogen blanket line connected to the pressure compensation line and supplying nitrogen gas to the pressure compensation line, an eleventh valve provided upstream of the connection point of the pressure compensation line with the nitrogen blanket line, a twelfth valve provided in the nitrogen blanket line, and a thirteenth valve provided downstream of the connection point of the pressure compensation line with the nitrogen blanket line, and the pressure in the gas-liquid separator is adjusted by supplying evaporated gas or nitrogen gas from the pressure compensation line.

[0021] Preferably, the eighth to tenth valves and the thirteenth valve are closed, the eleventh and twelfth valves are opened, nitrogen gas is supplied from the nitrogen blanket line, and the presence or absence of leakage in the high-pressure section of the heat exchanger through which the compressed gas passes via the reliquefaction line is confirmed. [Effects of the Invention]

[0022] The present invention makes it possible to quickly check for leaks of refrigerant or the like from heat exchangers or the lines connected to the heat exchangers during the process of filling the refrigerant circulation line with refrigerant during the initial start-up or restart of a reliquefaction system.

[0023] Furthermore, the leak detection system of the present invention eliminates the need to install additional equipment to detect leaks, thereby reducing the installation costs of the reliquefaction system and leak detection system. Furthermore, by opening and closing the valves provided in the lines connected to the heat exchanger, it is possible to check for refrigerant leaks from the heat exchanger or the lines connected to the heat exchanger during the process of filling the refrigerant circulation line with refrigerant, thereby shortening the start-up preparation time of the reliquefaction system and ensuring the safety of the ship. [Brief explanation of the drawings]

[0024] [Figure 1]10A to 10C are schematic diagrams illustrating a process for detecting leakage of refrigerant or the like from a heat exchanger and each line connected to the heat exchanger using a leakage detection system for a marine reliquefaction system according to an embodiment of the present invention. [Figure 2] 10A to 10C are schematic diagrams illustrating a process for detecting leakage of refrigerant or the like from a heat exchanger and each line connected to the heat exchanger using a leakage detection system for a marine reliquefaction system according to an embodiment of the present invention. [Figure 3] 10A to 10C are schematic diagrams illustrating a process for detecting leakage of refrigerant or the like from a heat exchanger and each line connected to the heat exchanger using a leakage detection system for a marine reliquefaction system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] The operational advantages of the present invention and the objects achieved by the embodiments of the present invention will now be described by way of example with reference to the drawings and the contents depicted in the drawings.

[0026] The configuration and operation of the embodiment of the present invention will be described below with reference to the drawings. Note that, with respect to the reference numerals given to components in each drawing, the same reference numerals are used to designate the same components in other drawings as far as possible.

[0027] The vessels of the embodiments of the present invention described below may be any type of vessel equipped with storage tanks for storing liquefied gas. Typical examples include self-propelled vessels such as LNG carriers, liquid hydrogen carriers, and LNG regasification vessels (RVs), as well as floating offshore structures without propulsion capabilities, such as LNG floating production storage offloading systems (FPSOs) and LNG floating storage regasification units (FSRUs).

[0028] Furthermore, this embodiment can liquefy gas at low temperatures for transportation and can be applied to the re-liquefaction cycle of all types of liquefied gases that generate evaporated gas during storage. Examples of such liquefied gases include liquefied natural gas (LNG), liquefied ethane gas (LEG), liquefied petroleum gas (LPG), liquefied ethylene gas, and liquefied propylene gas. Note that in the embodiments described below, LNG, one of the representative liquefied gases, will be used as an example.

[0029] Figures 1 to 3 schematically show the process of detecting leakage of refrigerant or the like from a heat exchanger and each line connected to the heat exchanger using a leakage detection system for a marine reliquefaction system according to an embodiment of the present invention.

[0030] The marine vessel reliquefaction system equipped with the leak detection system of this embodiment discharges evaporated gas generated from liquefied gas stored in a storage tank of the vessel from a vapor header VH, supplies the discharged evaporated gas to the onboard engine as fuel, and reliquefies the remaining evaporated gas that is not supplied as fuel and collects it in a storage tank CT.

[0031] As shown in Figures 1 to 3, the reliquefaction system in which the leak detection system of this embodiment is installed is provided with a gas supply line GSL that connects the vapor header VH and the compressor 100 and supplies the evaporated gas discharged from the storage tank CT to the compressor 100, a reliquefaction line RL that cools and re-liquefies the compressed gas obtained by compressing the evaporated gas in the compressor 100 in a heat exchanger 200 and recovers it in the storage tank CT, and a refrigerant circulation line CL that circulates a refrigerant that cools the compressed gas in the heat exchanger 200.

[0032] The refrigerant circulation line CL is provided with a refrigerant compressor 300 that cools the compressed gas in the heat exchanger 200 and then compresses the refrigerant discharged from the heat exchanger 200, and a refrigerant expander 350 that expands and cools the refrigerant compressed in the refrigerant compressor 300 and then cooled in the heat exchanger 200, and supplies the refrigerant to the heat exchanger 200. Also provided on board is an inventory tank that stores nitrogen gas, and a refrigerant filling line NL connects the inventory tank to the refrigerant circulation line CL on the upstream side of the refrigerant compressor 300.

[0033] The gas supply line GSL connects the storage tank and the compressor 100 via the heat exchanger 200. The gas supply line GSL allows the uncompressed evaporated gas discharged from the storage tank CT and before being supplied to the compressor 100 to be supplied to the heat exchanger 200 as a refrigerant, and then supplied to the compressor 100 where it is compressed.

[0034] The evaporative gas is compressed in the compressor 100, for example, to a pressure that is the fuel supply pressure of the ship's main engine. For example, the pressure is compressed to 5.5 barg if a DF engine is installed, to 15 barg if an X-DF engine is installed, and to 300 barg if an ME-GI engine is installed. The compressed evaporative gas is supplied as fuel to the ship's main engine (not shown), and the remaining evaporative gas that is not supplied as fuel is re-liquefied.

[0035] According to ship regulations, compressors that supply fuel to engines are required to have a redundant design (redundancy) in preparation for emergency situations. While the present embodiment will be described mainly using a single compressor as an example, the compressor may also be configured to include a main compressor and a standby compressor. Furthermore, the compressor may also be a multi-stage compressor that includes multiple compression sections and an intercooler.

[0036] The evaporated gas compressed by the compressor 100 is supplied to the heat exchanger 200 through a re-liquefaction line RL and cooled in the heat exchanger 200 .

[0037] The reliquefaction line RL is provided with a heat exchanger 200 that cools the evaporated gas compressed by the compressor 100, and a gas-liquid separator 400 that separates the evaporated gas cooled by the heat exchanger 200 into gas and liquid and supplies the separated liquefied gas to the storage tank CT.

[0038] The compressed evaporative gas is cooled in heat exchanger 200 by refrigerant circulating through refrigerant circulation line CL. Refrigerant circulation line CL is provided with a refrigerant expander 350, which expands and cools the refrigerant supplied to heat exchanger 200, and a refrigerant compressor 300, which compresses the refrigerant discharged from heat exchanger 200 after the evaporative gas is cooled in heat exchanger 200. The refrigerant compressor 300 and refrigerant expander 350 are connected via a shaft, and a compander type compressor is provided, which utilizes the expansion energy of the refrigerant to compress the refrigerant. This reduces the power required to drive the refrigeration cycle.

[0039] The refrigerant that circulates through the refrigerant circulation line CL and is supplied to the heat exchanger 200 is, for example, a nitrogen refrigerant (N2).

[0040] The nitrogen refrigerant compressed by the refrigerant compressor 300 is cooled by the heat exchanger 200, then cooled by expansion in the refrigerant expander 350, and is supplied again to the heat exchanger 200 as a refrigerant, and circulates through the refrigerant circulation line CL. As a result, in the heat exchanger 200, heat is exchanged among four flows: the evaporated gas compressed by the compressor 100, the uncompressed evaporated gas before being supplied to the compressor 100, the nitrogen refrigerant cooled by expansion in the refrigerant expander 350, and the nitrogen refrigerant compressed by the refrigerant compressor 300.

[0041] In addition, upstream of the heat exchanger 200 on the gas supply line GSL, a preheating line PHL is provided to adjust the temperature of the evaporated gas supplied to the heat exchanger 200 in order to minimize the thermal stress on the heat exchanger 200.

[0042] The preheating line PHL branches off from the gas supply line GSL upstream of the heat exchanger 200 of the gas supply line GSL, heats all or part of the evaporated gas, and supplies the heated evaporated gas to the gas supply line GSL upstream of the heat exchanger 200. The preheating line PHL is provided with a preheater 250 that heats the evaporated gas. Note that, for example, glycol water, steam, seawater, clean water (fresh water), etc. are supplied as a heat source for the preheater 250.

[0043] The evaporated gas that has passed through the preheating line PHL is combined with the evaporated gas that has not been supplied to the preheating line PHL but has passed through the gas supply line GSL, and is then supplied to the heat exchanger 200. The evaporated gas supplied to the heat exchanger 200 is compressed by the compressor 100, and then supplied to the heat exchanger 200 again, where it is cooled by heat exchange with the nitrogen refrigerant flowing through the refrigerant circulation line CL and the uncompressed evaporated gas flowing through the gas supply line GSL.

[0044] The evaporated gas cooled in the heat exchanger 200 is separated into gas and liquid in the gas-liquid separator 400, and the separated re-liquefied gas is supplied to the storage tank CT. In addition, downstream of the heat exchanger 200 on the re-liquefaction line RL, a bypass line BL is provided which branches off from the re-liquefaction line RL and bypasses the gas-liquid separator 400 to be connected to the storage tank CT. The bypass line BL also allows the re-liquefied gas cooled in the heat exchanger 200 to be supplied directly to the storage tank CT.

[0045] Here, when a valve provided downstream of the gas-liquid separator 400 is opened in order to supply the reliquefied gas in the gas-liquid separator 400 to the storage tank CT, the pressure inside the gas-liquid separator 400 changes. Even in such a case, the pressure inside the gas-liquid separator 400 can be maintained by using flash gas (i.e., off-gas) generated from the reliquefied gas supplied into the gas-liquid separator 400, thereby allowing the reliquefied gas in the gas-liquid separator 400 to be supplied to the storage tank CT.

[0046] In this case, if the liquefied gas cooled by heat exchange with the nitrogen refrigerant becomes supercooled and is supplied to the gas-liquid separator 400, almost no off-gas is generated, and opening the valve downstream of the gas-liquid separator 400 may cause a sudden drop in pressure within the gas-liquid separator 400. To compensate for the pressure within the gas-liquid separator 400 and maintain the pressure within the gas-liquid separator 400 even in such a case, the re-liquefaction system equipped with the leak detection system of this embodiment is provided with a pressure compensation line PL that branches off from the re-liquefaction line RL downstream of the compressor 100 of the re-liquefaction line RL and connects to the top of the gas-liquid separator 400, and a nitrogen blanket line BKL that supplies nitrogen gas to the pressure compensation line PL. Thus, when the re-liquefied gas within the gas-liquid separator 400 is supplied to the storage tank CT, the pressure within the gas-liquid separator 400 is maintained by supplying evaporated gas or nitrogen gas to the gas-liquid separator 400 through the pressure compensation line PL.

[0047] In a reliquefaction system equipped with the leak detection system of this embodiment, it is necessary to fill the refrigerant circulation line CL of the reliquefaction system with nitrogen refrigerant prior to starting the reliquefaction process, when the reliquefaction process is initially started or when the reliquefaction process is restarted after being stopped.

[0048] When charging the refrigerant circulation line CL with nitrogen refrigerant, the nitrogen refrigerant is supplied from the refrigerant charging line NL to the refrigerant circulation line CL upstream of the refrigerant compressor 300. In this embodiment, during the process of charging the refrigerant circulation line CL with refrigerant, leakage of the refrigerant, etc. from the heat exchanger 200 and each line connecting to the heat exchanger 200 can be simultaneously detected. This shortens the preparation time required to start the re-liquefaction process and ensures the safety of the ship.

[0049] The reliquefaction system is provided with valves for opening and closing each line (piping), and in this embodiment, by operating the opening and closing of these valves, it is possible to check for leakage of refrigerant, etc. from the heat exchanger 200 and each line (piping) connected to the heat exchanger 200 during the process of filling the refrigerant circulation line CL with refrigerant.

[0050] 1 to 3, a first valve V1 is provided on the refrigerant circulation line CL upstream of the connection point with the refrigerant charging line NL. A second valve V2 is provided on the refrigerant circulation line CL between the refrigerant expander 350 and the heat exchanger 200. A third valve V3 is provided on the refrigerant charging line NL.

[0051] A fourth valve V4 is provided on the gas supply line GSL upstream of the heat exchanger 200. A fifth valve V5 is provided on the gas supply line GSL downstream of the heat exchanger 200 and upstream of the compressor 100 (i.e., between the heat exchanger 200 and the compressor 100). The preheating line PHL branches off from the gas supply line GSL upstream of the fourth valve V4 of the gas supply line GSL. A sixth valve V6 is provided on the preheating line PHL downstream of the preheater 250. A seventh valve V7 is provided on a line that branches off from the preheating line PHL downstream of the preheater 250, bypasses the heat exchanger 200, and is connected to the gas supply line GSL upstream of the compressor 100.

[0052] An eighth valve V8 is provided on the reliquefaction line RL upstream of the heat exchanger 200. A ninth valve V9 is provided on the reliquefaction line RL upstream of the gas-liquid separator 400. A tenth valve V10 is provided on the bypass line BL branching off from the reliquefaction line RL upstream of the ninth valve V9.

[0053] An eleventh valve V11 is provided upstream of the connection point of the pressure compensation line PL with the nitrogen blanket line BKL. A twelfth valve V12 is provided in the nitrogen blanket line BKL. A thirteenth valve V13 is provided downstream of the connection point of the pressure compensation line PL with the nitrogen blanket line BKL.

[0054] Below, with reference to Figures 1 to 3, we will explain a method for detecting leakage of refrigerant, etc. from heat exchanger 200 and each line connected to heat exchanger 200 when the reliquefaction process is initially started or when the reliquefaction process is restarted after being stopped.

[0055] First, as shown in Figure 1, when the reliquefaction process is initially started or restarted after being stopped, nitrogen gas stored in the inventory tank is filled into the refrigerant circulation line CL as nitrogen refrigerant prior to starting the reliquefaction process.

[0056] At this time, the first and second valves V1 and V2 are closed, and the third valve V3 is opened. Nitrogen gas in the inventory tank is supplied from the refrigerant filling line NL to the refrigerant circulation line CL from the upstream side of the refrigerant compressor 300 of the refrigerant circulation line CL. First, it is checked whether there is any leakage of nitrogen refrigerant from the section of the refrigerant circulation line CL between the high-pressure section downstream of the refrigerant compressor 300 and the low-pressure section downstream of the refrigerant expander 350.

[0057] In parallel with the leak detection for the refrigerant circulation line CL, the fourth and fifth valves V4 and V5 can be closed to check for leakage from the low-pressure section of the heat exchanger 200 through which the evaporated gas passes via the gas supply line GSL, and the eighth to tenth valves V8, V9, and V10 can be closed to check for leakage from the high-pressure section of the heat exchanger 200 through which the evaporated gas passes via the reliquefaction line RL. At this time, the sixth and seventh valves V6 and V7 and the eleventh to thirteenth valves V11, V12, and V13 are also closed.

[0058] After leak detection is completed for the portion of the refrigerant circulation line CL shown in FIG. 1 from the position where the first valve V1 is installed to the position where the second valve V2 is installed, including the section from the high-pressure section downstream of the refrigerant compressor 300 to the low-pressure section downstream of the refrigerant expander 350, the first and second valves V1 and V2 are then opened to check for leaks in the remaining portion of the refrigerant circulation line CL shown in FIG. 2.

[0059] Specifically, the first and second valves V1 and V2 are opened, nitrogen refrigerant is filled into the refrigerant circulation line CL, and it is checked whether or not there is any leakage of nitrogen refrigerant from the section between the low-pressure section downstream of the refrigerant expander 350 and the low-pressure section upstream of the refrigerant compressor 300, including the low-temperature section of the heat exchanger 200 through which the nitrogen refrigerant passes via the refrigerant circulation line CL.

[0060] As described above, in parallel with detecting leaks in the refrigerant circulation line CL, the fourth and fifth valves V4, V5 and the eighth to tenth valves V8, V9, V10 can be closed to check for leaks from the low-pressure section of the heat exchanger 200 through which the evaporated gas passes via the gas supply line GSL, or the high-pressure section of the heat exchanger 200 through which the evaporated gas passes via the re-liquefaction line RL.

[0061] Furthermore, once the leak detection for the refrigerant circulation line CL is completed, the refrigerant circulation line CL continues to be filled with nitrogen refrigerant, and nitrogen gas for pressure compensation is filled into the gas-liquid separator 400 via the nitrogen blanket line BKL, and the presence or absence of nitrogen gas leakage from the high-pressure section of the heat exchanger 200 through which the compressed gas being reliquefied passes via the reliquefaction line RL is confirmed.

[0062] Specifically, as shown in Figure 3, the eighth to tenth valves V8, V9, V10 and the thirteenth valve V13 are closed, and the eleventh and twelfth valves V11 and V12 are opened to supply nitrogen gas from the nitrogen blanket line BKL and send the nitrogen gas upstream of the heat exchanger 200 in the reliquefaction line RL, and check for any leakage of nitrogen gas from the high-pressure section of the heat exchanger 200 through which the compressed gas being reliquefied via the reliquefaction line RL passes.

[0063] When the leak detection of the high-pressure section of the heat exchanger 200 is completed, nitrogen gas is supplied to the gas-liquid separator 400 and filled into the gas-liquid separator 400 as nitrogen gas for pressure compensation.

[0064] As described above, in the leak detection system of this embodiment, by operating the opening and closing of the valves provided in each line during the process of filling the refrigerant circulation line CL with refrigerant, which is performed prior to the initial start or restart of the reliquefaction process, it is possible to simultaneously detect leaks in the heat exchanger 200 and each line connected to the heat exchanger 200. This shortens the preparation time for starting the reliquefaction process and ensures the safety of the ship.

[0065] The present invention is not limited to the above-described embodiments, and it will be obvious to those skilled in the art to which the present invention pertains that various changes or modifications can be made without departing from the technical gist of the present invention.

Claims

1. a gas supply line for supplying evaporated gas generated from liquefied gas stored in a storage tank of the ship to the compressor; and a re-liquefaction line in which the compressed gas obtained by compressing the evaporated gas in the compressor is cooled in a heat exchanger to be re-liquefied and returned to the storage tank; and a refrigerant circulation line through which a refrigerant that cools the compressed gas in the heat exchanger circulates; and a refrigerant compressor provided in the refrigerant circulation line and configured to compress the refrigerant discharged from the heat exchanger after the compressed gas has been cooled by the heat exchanger; and a refrigerant expander that expands and cools the refrigerant compressed by the refrigerant compressor and then supplied to and cooled in the heat exchanger, and supplies the cooled refrigerant to the heat exchanger; and a refrigerant filling line connecting an inventory tank filled with nitrogen gas and the refrigerant circulation line on an upstream side of the refrigerant compressor; At the initial start or restart of the reliquefaction process, nitrogen gas is supplied from the refrigerant charging line to the refrigerant circulation line upstream of the refrigerant compressor to check for leakage in the refrigerant circulation line; a first valve provided upstream of a connection point of the refrigerant circulation line with the refrigerant charging line; and a second valve provided in the refrigerant circulation line between the refrigerant expander and the heat exchanger, upstream of the first valve; and a third valve provided in the refrigerant charging line; Leak detection system for marine reliquefaction systems.

2. the first and second valves are closed, the third valve is opened, nitrogen gas is supplied to the refrigerant circulation line, and it is confirmed whether there is any leakage from the low pressure section of the refrigerant circulation line upstream of the refrigerant compressor to the low pressure section of the refrigerant circulation line downstream of the refrigerant expander, and then the first and second valves are opened to fill the refrigerant circulation line with nitrogen refrigerant, and it is confirmed whether there is any leakage from the low pressure section of the refrigerant circulation line downstream of the refrigerant expander to the low pressure section of the refrigerant circulation line upstream of the refrigerant compressor. The leak detection system for a marine reliquefaction system according to claim 1.

3. the gas supply line is connected to the compressor via the heat exchanger; a fourth valve provided on the gas supply line upstream of the heat exchanger; and a fifth valve provided in the gas supply line between the heat exchanger and the compressor; At the time of initial start or restart of the reliquefaction process, the fourth and fifth valves are closed, and in parallel with checking for leakage in the refrigerant circulation line, the presence or absence of leakage in the low pressure section of the heat exchanger through which the evaporated gas passes via the gas supply line is checked. The leak detection system for a marine reliquefaction system according to claim 1.

4. a preheating line branching off from the gas supply line at a position upstream of the fourth valve of the gas supply line and connected between the fourth valve of the gas supply line and the heat exchanger; and a preheater provided in the preheat line for heating the evaporated gas passing through the preheat line; and a sixth valve provided on the preheating line downstream of the preheater; and a seventh valve provided in a line that branches off from the preheating line between the preheater and the sixth valve, bypasses the heat exchanger, and is connected to the gas supply line upstream of the compressor, The leak detection system for a marine reliquefaction system according to claim 3.

5. a gas-liquid separator provided on the reliquefaction line downstream of the heat exchanger, for separating the reliquefied gas into gas and liquid; and a bypass line branching off from the reliquefaction line downstream of the heat exchanger, bypassing the gas-liquid separator and connected to a storage tank; and an eighth valve provided on the reliquefaction line upstream of the heat exchanger; and a ninth valve provided between the branch point of the bypass line of the reliquefaction line and the gas-liquid separator; and a tenth valve provided in the bypass line; At the time of initial start or restart of the reliquefaction process, the eighth to tenth valves are closed, and in parallel with checking for leakage in the refrigerant circulation line, the presence or absence of leakage in the high-pressure section of the heat exchanger through which the compressed gas passes via the reliquefaction line is checked. The leak detection system for a marine reliquefaction system according to claim 3.

6. a pressure compensation line branching off from the reliquefaction line between the compressor and the heat exchanger of the reliquefaction line and connected to an upper portion of the gas-liquid separator; and a nitrogen blanket line connected to the pressure compensation line and supplying nitrogen gas to the pressure compensation line; and an eleventh valve provided upstream of the connection point of the pressure compensation line with the nitrogen blanket line; and a twelfth valve provided in the nitrogen blanketing line; and a thirteenth valve provided downstream of the connection point of the pressure compensation line with the nitrogen blanket line; The pressure in the gas-liquid separator is adjusted by supplying evaporation gas or nitrogen gas through the pressure compensation line. The leak detection system for a marine reliquefaction system according to claim 5.

7. the eighth to tenth valves and the thirteenth valve are closed, the eleventh and twelfth valves are opened, nitrogen gas is supplied from the nitrogen blanketing line, and the presence or absence of leakage from the high-pressure section of the heat exchanger through which the compressed gas passes through the heat exchanger via the reliquefaction line is confirmed. The leak detection system for a marine reliquefaction system according to claim 6.

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