KR20120103406A - System and method for supplying fuel for high pressure natural gas injection engine - Google Patents

Abstract

PURPOSE: A system and method for supplying fuel for a high pressure natural gas injection engine are provided to reduce the thermal loads of a heat medium for evaporation. CONSTITUTION: A system for supplying fuel for a high pressure natural gas injection engine comprises a compressing unit(13) for evaporation gas, a re-liquefaction unit(20), a high pressure pump(33), a high pressure vaporizer(37), and a heat exchanger. The re-liquefaction unit comprises a cold box(21), a compressing unit, an expansion unit, a gas-liquid separator(22). The cold box heat exchanges refrigerants with the evaporation gas. The compressing unit compresses the refrigerants heated in the cold box. The expansion unit decreases the temperature of the compressed refrigerants. The gas-liquid separator separates gas and liquid from the refrigerants.

Description

Fuel supply system and method for high pressure natural gas injection engine {SYSTEM AND METHOD FOR SUPPLYING FUEL FOR HIGH PRESSURE NATURAL GAS INJECTION ENGINE}

The present invention relates to a fuel supply system and a supply method of a high pressure natural gas injection engine, and more particularly, it is discarded after being used for reliquefaction of boil-off gas in offshore structures using a high pressure natural gas injection engine, such as a ME-GI engine. Relates to a fuel supply system and method for a high pressure natural gas injection engine capable of recovering liquefied energy and reducing the overall energy requirement for reliquefaction.

Recently, the consumption of liquefied gas such as LNG (Liquefied Natural Gas) and LPG (Liquefied Petroleum Gas) is increasing worldwide. The liquefied gas is transported in a gas state through a gas pipe on land or sea, or transported to a distant consumer while stored in a liquefied gas carrier in a liquefied state. Liquefied gas such as LNG or LPG is obtained by cooling natural gas or petroleum gas to cryogenic temperature (approximately -163 ℃ in case of LNG), and its volume is greatly reduced than in gas state, so it is very suitable for long distance transportation by sea. .

Liquefied gas carriers are used to load liquefied gas into the sea and unload this liquefied gas to land requirements. To this end, a liquefied gas carrier includes a storage tank (commonly referred to as a cargo hold) that can withstand the cryogenic temperature of liquefied gas. do.

Examples of offshore structures in which storage tanks for storing liquefied gas in such a cryogenic state are provided include vessels such as LNG Regasification Vessel (LV RV), LNG Floating Storage and Regasification Unit (FSRU), LNG Floating, Production, Structures such as storage and off-loading).

LNG RV is a LNG regasification facility installed on a liquefied gas carrier that can be self-driving and floating. LNG FSRU stores liquefied natural gas, which is unloaded from LNG carriers, in a storage tank after liquefaction as needed. It is an offshore structure that vaporizes natural gas and supplies it to land demand. In addition, LNG FPSO is a marine structure that is used to directly purify mined natural gas from the sea and liquefy directly to store it in a storage tank, and to transfer LNG stored in the storage tank to an LNG carrier if necessary. In the present specification, the offshore structure is a concept including not only vessels such as liquefied gas carriers and LNG RVs but also structures such as LNG FPSO and LNG FSRU.

The liquefaction temperature of natural gas is about -163 ° C at ambient pressure, so LNG is evaporated even if its temperature is slightly higher than -163 ° C at normal pressure. In the case of a conventional LNG carrier, for example, the LNG storage tank of the LNG carrier is insulated, but since the external heat is continuously transmitted to the LNG, LNG is transported while the LNG carrier is transporting the LNG. Boil-off gas (BOG) is generated in the LNG storage tank by continuously vaporizing it in the LNG storage tank.

Since the generated boil-off gas increases the pressure in the storage tank and accelerates the flow of the liquefied gas in response to the fluctuation of the vessel, it may cause structural problems, so it is necessary to suppress the generation of the boil-off gas.

Conventionally, in order to suppress evaporated gas in a storage tank of a liquefied gas carrier, a method of discharging the evaporated gas to the outside of the storage tank for incineration, and discharging the evaporated gas to the outside of the storage tank to reliquefy through a reliquefaction apparatus. And the method of returning to the storage tank again, using the boil-off gas as fuel used in the ship's propulsion engine, and suppressing the generation of the boil-off gas by maintaining the internal pressure of the storage tank alone or in combination. It was used.

In the case of a conventional offshore structure equipped with a boil-off gas reliquefaction device, the boil-off gas inside the storage tank is discharged to the outside of the storage tank in order to maintain an appropriate pressure in the storage tank to be re-liquefied through the re-liquefaction device. The evaporated gas is compressed to a low pressure of approximately 4 to 8 bara and fed to the reliquefaction apparatus before it is done. The compressed boil-off gas is liquefied through heat exchange with nitrogen cooled to cryogenic temperatures in a reliquefaction apparatus including a nitrogen refrigeration cycle and then returned to the storage tank.

In order to increase the efficiency of reliquefaction of the boil-off gas, it is preferable to compress the boil-off gas to a high pressure. However, since the LNG stored in the storage tank is kept at a normal pressure, if the pressure of the re-liquefied liquefied liquefied gas is too high, When flash gas (flash gas) is generated. Therefore, although the re-liquefaction efficiency is low, there is a problem in that the boil-off gas can be compressed at a low pressure of about 4 to 8 bara.

That is, as shown in FIG. 1, conventionally, after supplying the boil-off gas generated in the storage tank, that is, NBOG to the boil-off gas compressor and compressing it to a low pressure of about 4 to 8 bara, the low-pressure BOG is a nitrogen gas refrigerant. It is supplied to the reliquefaction apparatus used. In the reliquefaction apparatus, the liquefied boil-off gas, that is, LBOG, had a problem in that flash gas was generated when it returned to the storage tank, thereby compressing the pressure of the boil-off gas to a low pressure in the boil-off gas compressor.

In addition, a method of using evaporated gas generated in a storage tank as a fuel used in a propulsion engine of a ship has been known. As a conventional propulsion engine capable of using evaporated gas as a fuel, an engine such as a steam turbine or a DFDE is known. there was. By the way, steam turbines and DFDEs can consume the boil-off gas compressed at a pressure of several bar to several tens of bar as fuel, but they are less efficient than diesel engines using heavy oil as fuel. There were many problems that had to be pre-empted to be used as a driving agency.

As a result, conventionally, the evaporated gas generated from the storage tank is re-liquefied through the reliquefaction apparatus and then returned to the storage tank. As a typical method of treating the evaporated gas, the flash gas is generated as much as possible. The basic concept was to not raise the pressure of the re-liquefied boil-off gas to suppress it.

As the reliquefaction apparatus for reliquefying the boil-off gas, those disclosed in WO 2007/117148 and WO 2009/136793 can be used.

In addition, conventionally, a nitrogen refrigeration cycle, a mixed refrigerant cycle, and the like are used to reliquefy the boil-off gas. However, the nitrogen refrigeration cycle has a problem of low liquefaction efficiency using nitrogen gas (N ₂ ) as a refrigerant. Since a refrigerant in which nitrogen and a hydrocarbon gas, etc. are mixed as the refrigerant is used, there is a problem of inferior stability.

More specifically, in a conventional LNG reliquefaction apparatus such as a ship or a marine plant, a turbo expander-type nitrogen reverse Brayton cycle was implemented to reliquefy the boil-off gas, and a mixed refrigerant in a land LNG liquefaction plant. A Joule-Thompson refrigeration cycle was implemented to liquefy natural gas. Nitrogen reverse Brayton cycles used for marine use are advantageous in ships or offshore structures where space is limited due to their relatively simple configuration, but have low efficiency. The mixed refrigerant Joule-Thomson refrigeration cycles used for land use are relatively Although the efficiency is high, due to the characteristics of the mixed refrigerant, there is a problem in that the device configuration is complicated, such as the use of a separator to separate when a gas-liquid state exists at the same time.

In addition, for offshore structures equipped with storage tanks for storing liquefied gas such as LNG, research and development on how to efficiently treat the evaporated gas continuously generated in the storage tanks and suppress the generation of flash gas It needs to be done over and over again.

The present invention is to solve the conventional problems as described above, while utilizing the boil-off gas generated from the liquefied gas storage tank as a fuel of a high-pressure natural gas injection engine, for example, ME-GI engine, used to re-liquefy the boil-off gas It is to provide a fuel supply system and a supply method for a high-pressure natural gas injection engine that can recover the liquefied energy that is discarded afterwards to reduce the total energy required for reliquefaction.

According to an aspect of the present invention for achieving the above object, the evaporation gas compression unit for compressing the evaporation gas generated in the storage tank received from the storage tank, the liquefied gas supplied by the evaporation gas compressed in the evaporation gas compression unit A high pressure natural gas injection engine comprising a reliquefaction apparatus, a high pressure pump for compressing liquefied liquefied gas liquefied in the reliquefaction apparatus, and a high pressure vaporizer for vaporizing liquefied liquefied gas compressed in the high pressure pump. A system comprising: cooling an evaporation gas by heat-exchanging an evaporation gas compressed by the evaporation gas compression unit with a liquefied evaporation gas compressed by the high pressure pump, and supplying the liquefied evaporation gas to the high pressure vaporizer. And a heat exchanger, wherein the reliquefaction apparatus includes a heat bridge between a refrigerant and an evaporation gas. The cold box, compression means for compressing the refrigerant heated in the cold box, expansion means for reducing the temperature by expanding the compressed refrigerant, and refrigerant gas-liquid separator for separating the refrigerant in the gas state and the liquid state Provided is a fuel supply system for a high pressure natural gas injection engine comprising a.

The fuel supply system preferably further includes a buffer tank for receiving a cooled and liquefied liquefied evaporation gas from the reliquefaction apparatus to separate gaseous components and supply only liquid components to the high pressure pump.

The boil-off gas compressor may include at least one boil-off gas compressor for compressing the boil-off gas and at least one intermediate cooler for cooling the boil-off gas whose temperature has risen while being compressed by the boil-off gas compressor.

The boil-off gas generated and discharged from the storage tank is preferably compressed to 12 to 45 bara (absolute pressure) in the boil-off gas compression unit and then supplied to the reliquefaction apparatus.

The reliquefaction apparatus includes a plurality of refrigerant gas-liquid separators, and among the plurality of refrigerant gas-liquid separators, the refrigerant gas-liquid separator disposed at the downstream side is a gaseous refrigerant and a liquid state separated from the refrigerant gas-liquid separator disposed upstream. It is preferable that the refrigerants of the mixture are supplied after being mixed again.

The gaseous refrigerant separated from the refrigerant gas-liquid separator disposed upstream of the plurality of refrigerant gas-liquid separators is compressed by the refrigerant compressor and cooled by the refrigerant cooler before being supplied to the refrigerant gas-liquid separator disposed most downstream. It is preferable to go through.

In addition, according to another aspect of the present invention, the evaporated gas generated in the storage tank for storing the liquefied gas is discharged from the storage tank and compressed, liquefied compressed boiled gas in the reliquefaction apparatus, liquefied liquefied evaporation gas Is a fuel supply method for compressing the gas to a high pressure and then vaporizing and supplying it as a fuel to the high pressure natural gas injection engine, wherein the reliquefaction apparatus is configured to compress a cold box in which heat exchange between a refrigerant and an evaporation gas is performed, And a plurality of refrigerant gas-liquid separators for separating the refrigerant in the gaseous state and the liquid state, and an expansion means for expanding the compressed refrigerant to lower the temperature, and the most downstream of the plurality of refrigerant gas-liquid separators. The refrigerant gas-liquid separator disposed in the gaseous phase separator separated from the refrigerant gas-liquid separator disposed upstream Provided is a fuel supply method for a high pressure natural gas injection engine, wherein the refrigerant and the liquid refrigerant are mixed again and supplied.

In the fuel supply method, it is preferable to reduce the energy for liquefying the boil-off gas by recovering and using the liquefied energy of the liquefied boil-off gas by heat-exchanging the boil-off gas before liquefaction with the liquefied evaporation gas before vaporization.

According to the present invention, while using the evaporated gas generated from the liquefied gas storage tank as a fuel of a high-pressure natural gas injection engine, such as a ME-GI engine, to recover the liquefied energy that is discarded after being used for the reliquefaction of the boil-off gas for reliquefaction A fuel supply system and method can be provided for a high pressure natural gas injection engine that can reduce the overall energy requirement required.

According to the fuel supply system and method for a high-pressure natural gas injection engine of the present invention, it is possible to save the liquefied energy by recovering and utilizing the cold heat used for the reliquefaction of the boil-off gas.

Further, according to the fuel supply system and method for a high pressure natural gas injection engine of the present invention, the heat load of the heat medium required for vaporization can be reduced in the step of vaporizing liquefied evaporation gas for supplying as a fuel to the high pressure natural gas injection engine. Will be.

1 is a schematic block diagram for explaining a method for treating boil-off gas through re-liquefaction of boil-off gas according to the prior art;
2 is a schematic block diagram for explaining a method for treating boil-off gas through fuel supply according to the present invention;
3A is a configuration diagram showing a fuel supply system for a high pressure natural gas injection engine according to the first embodiment of the present invention;
3B is a configuration diagram showing a fuel supply system for a high pressure natural gas injection engine according to a modification of the first embodiment of the present invention;
Figure 4a is a graph showing the freezing point and boiling point of the components contained in the non-explosive mixed refrigerant of the present invention,
Figure 4b is a graph showing the freezing point and boiling point of the components contained in the hydrocarbon mixed refrigerant,
Figure 4c is a graph showing the liquefaction temperature according to the pressurized pressure of natural gas,
5 is a graph showing boiling points of refrigerant components for constructing a non-explosive mixed refrigerant;
Figure 6 is a graph comparing the power consumption when using the non-explosive mixed refrigerant refrigeration cycle and the nitrogen gas refrigeration cycle in the reliquefaction apparatus of the boil-off gas,
7A is a configuration diagram showing a fuel supply system for a high pressure natural gas injection engine according to a second embodiment of the present invention;
7B is a block diagram showing a fuel supply system for a high pressure natural gas injection engine according to a modification of the second embodiment of the present invention;
8A is a block diagram showing a fuel supply system for a high pressure natural gas injection engine according to a third embodiment of the present invention;
8B is a block diagram showing a fuel supply system for a high pressure natural gas injection engine according to a modification of the third embodiment of the present invention;
9A is a configuration diagram showing a fuel supply system for a high pressure natural gas injection engine according to a fourth embodiment of the present invention;
9B is a configuration diagram showing a fuel supply system for a high pressure natural gas injection engine according to a modification of the fourth embodiment of the present invention;
10A is a configuration diagram showing a fuel supply system for a high pressure natural gas injection engine according to a fifth embodiment of the present invention; and
10B is a configuration diagram showing a fuel supply system for a high pressure natural gas injection engine according to a modification of the fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the following examples can be modified in various forms, and the scope of the present invention is not limited to the following examples.

In general, it is nitrogen oxides (NOx) and sulfur oxides (SOx) that are regulated by the International Maritime Organization among the waste gas discharged from ships, and is trying to regulate the emission of carbon dioxide (CO ₂ ). Particularly, in the case of nitrogen oxide (NOx) and sulfur oxides (SOx), it was submitted through the Protocol of the Maritime Pollution Prevention Convention (MARPOL) in 1997, In May, the requirements for the fermentation were satisfied and the regulations are being implemented.

Therefore, in order to meet these regulations, various methods have been introduced to reduce NOx emissions. Among these methods, a high pressure natural gas injection engine, for example, a ME-GI engine, has been developed and used for LNG carriers. .

Such ME-GI engines are marine structures such as LNG carriers for storing and transporting LNG (Liquefied Natural Gas) in cryogenic storage tanks. It can be installed in a marine plant such as LNG FPSO and LNG FSRU.) In this case, natural gas is used as fuel, and high pressure of about 150 ~ 400 bara (absolute pressure) depending on the load. Gas supply pressure is required.

Even for offshore structures equipped with high pressure natural gas injection engines, such as ME-GI engines, a reliquefaction device is still needed to treat Boil Off Gas (BOG) from LNG storage tanks. . In the case of a conventional offshore structure equipped with both a high-pressure natural gas injection engine such as a ME-GI engine and a reliquefaction device for treating boil-off gas, the boil-off gas is changed depending on the change in gas and fuel oil prices and the degree of regulation of exhaust gas. Can be used as a fuel or to liquefy evaporated gas to a storage tank and use heavy fuel oil (HFO) .In particular, it is possible to easily vaporize LNG when passing through certain regulated waters. It has the advantage of being able to be used as fuel, and is the next-generation eco-friendly engine, which can reach 50% efficiency and can be used as the main engine of LNG carriers in the future.

2 is a schematic block diagram illustrating a fuel supply method according to the present invention. According to the fuel supplying method of the present invention, after supplying the boil-off gas generated from the storage tank, that is, NBOG to the boil-off gas compressor and compressing it to medium pressure of about 12 to 45 bara, the medium pressure BOG is a non-flammable mixed refrigerant (Non Flammable). Mixed Refrigerant) is supplied to the reliquefaction apparatus using the refrigerant. The liquefied boil-off gas, LBOG, in the reliquefaction apparatus is compressed to the pressure required by the ME-GI engine in the fuel supply system (high pressure of about 400 bara, for example) and then supplied as fuel to the ME-GI engine. According to the present invention, since the LBOG supplied to the fuel supply system in the reliquefaction apparatus does not return to the storage tank, it is possible to prevent a problem of generating flash gas as in the prior art, and thus, the pressure of the boil-off gas in the evaporative gas compressor. Can be compressed to medium pressure.

In the present specification, the pressure range of the high pressure means a pressure of about 150 to 400 bara, which is a fuel supply pressure required by the high pressure natural gas injection engine, and the pressure range of the medium pressure means the evaporation in the evaporation gas compression unit 13. The pressure ranges from about 12 to 45 bara to compress the gas, and the low pressure means the pressure range from about 4 to 8 bara to compress to supply the boil-off gas to the reliquefaction apparatus in the prior art.

(First embodiment)

FIG. 3A is a block diagram showing a fuel supply system of an offshore structure, in particular a liquefied natural gas carrier, having a high pressure natural gas injection engine, such as a ME-GI engine, according to a first embodiment of the present invention. 3A shows an example in which a fuel supply system for a high pressure natural gas injection engine of the present invention is applied to an LNG carrier equipped with a ME-GI engine capable of using natural gas as a fuel, but for the high pressure natural gas injection engine of the present invention The fuel supply system can be applied to all types of offshore structures with liquefied gas storage tanks, namely ships such as LNG carriers, LNG RVs, as well as offshore plants such as LNG FPSOs and LNG FSRUs.

According to the fuel supply system of the offshore structure having the high pressure natural gas injection engine according to the first embodiment of the present invention, the boil-off gas (NBOG) generated and discharged from the liquefied gas storage tank 11 is the boil-off gas compression unit 13. ) Is compressed to a medium pressure of about 12 to 45 bara (absolute pressure) and then supplied to the reliquefaction apparatus 20. The liquefied liquefied gas (LBOG), which is supplied with liquefied energy, that is, cold heat from the reliquefaction apparatus 20, is compressed to a high pressure of about 150 to 400 bara by a high pressure pump 33, and then, to the high pressure vaporizer 37. Supplied. The boil-off gas vaporized in the high pressure vaporizer 37 is subsequently supplied as fuel to a high pressure natural gas injection engine, such as a ME-GI engine.

The liquefied evaporation gas (ie, liquefied natural gas) compressed to a high pressure by the high pressure pump 33 is in a supercritical pressure state, and thus it is virtually indistinguishable from liquid phase and gas phase. However, in the present specification, it is expressed as vaporizing the heating of the liquefied evaporation gas to the ambient temperature (or the temperature required by the high-pressure natural gas injection engine) in the high pressure state, the high-pressure device for heating the liquefied evaporation gas to the ambient temperature in the high pressure state Express it as a carburetor.

Storage tanks are equipped with sealed and insulated barriers to store liquefied gases, such as LNG, in cryogenic conditions, but they cannot completely block heat from the outside. Accordingly, the liquefied gas is continuously evaporated in the storage tank 11, and the evaporated gas is discharged through the evaporated gas discharge line L1 to maintain the pressure of the evaporated gas at an appropriate level. Let's do it.

The discharged boil-off gas is supplied to the boil-off gas compression unit 13 through the boil-off gas discharge line L1. The boil-off gas compressor 13 includes one or more boil-off gas compressors 14 and one or more intermediate coolers 15 for cooling the boil-off gas whose temperature has risen while being compressed by the boil-off gas compressor 14. In FIG. 3A there is illustrated a 5-stage compressed boil-off gas compression unit 13 comprising five boil-off gas compressors 14 and five intermediate coolers 15.

The boil-off gas compressed by the boil-off gas compression unit 13 is supplied to the reliquefaction apparatus 20 through the boil-off gas supply line L2. The boil-off gas supplied to the reliquefaction apparatus 20 is cooled by the refrigerant and reliquefied while passing through the cold box 21 of the reliquefaction apparatus 20. As the reliquefaction apparatus 20, any structure can be used as long as it can liquefy evaporated gas generated from liquefied gas such as LNG.

The evaporated gas re-liquefied through heat exchange in the cold box 21 is separated into a gas and a liquid state in the buffer tank 31, and only the liquid liquefied evaporation gas in the liquid state is supplied to the high pressure pump 33 through the fuel supply line L3. Is supplied. The high pressure pump 33 may be provided in plural, for example two in parallel.

In the high pressure pump 33, liquefied evaporation gas is pressurized to a fuel supply pressure required by a high pressure natural gas injection engine (for example, a ME-GI engine) and sent out. The liquefied evaporation gas sent from the high pressure pump 33 has a high pressure of about 150 to 400 bara (absolute pressure).

The reliquefaction apparatus 20 illustrated in FIG. 3A includes a cold box 21 for reliquefying the boil-off gas by heat exchange between the refrigerant and the boil-off gas, and a refrigerant partially heated and vaporized in the cold box 21. At least one refrigerant gas-liquid separator 22 for separating gaseous and liquid refrigerants, at least one refrigerant compressor 23 for compressing the gaseous refrigerant separated from the refrigerant gas-liquid separator 22, A refrigerant cooler 24 for cooling the refrigerant compressed by the refrigerant compressor 23, and a refrigerant expansion valve 25 for expanding the refrigerant cooled in the refrigerant cooler 24 after being compressed by the refrigerant compressor 23 to lower the temperature. And a refrigerant pump 26 for supplying the refrigerant in the liquid state separated from the refrigerant gas-liquid separator 22 to the refrigerant expansion valve 25.

The refrigerant supplied to the refrigerant expansion valve 25 through the refrigerant pump 26 is mixed with the refrigerant supplied to the refrigerant expansion valve 25 after passing through the refrigerant cooler 24 upstream of the refrigerant expansion valve 25. It is preferable.

On the other hand, the refrigerant supplied to the refrigerant expansion valve 25 may be configured to exchange heat with the refrigerant in the cryogenic state after expansion while passing through the cold box 21 before expansion.

In addition, the refrigerant cooled in the refrigerant cooler 24 may be supplied to another refrigerant gas-liquid separator to be processed into a refrigerant in a gas state and a refrigerant in a liquid state. To this end, the reliquefaction apparatus 20 of FIG. 3A is illustrated as including two refrigerant gas-liquid separators 22, a refrigerant compressor 23, a refrigerant cooler, and a refrigerant pump 26, but this is intended to explain the present invention. It is not limited and the number of installations can be added or subtracted as needed in the design.

(Modified example of the first embodiment)

3b shows a fuel supply system according to a variant of the first preferred embodiment of the invention. Since the structure of the boil-off gas compression part 13 and the reliquefaction apparatus 20 differs in part from the 1st embodiment mentioned above in the modified example of this 1st embodiment, only the difference is demonstrated below.

The boil-off gas compression section 13 according to the modification of the first embodiment illustrated in FIG. 3B is the same as that shown in FIG. 3A in that it has five boil-off gas compressors 14, but the boil-off gas compression section ( 3A differs from that illustrated in FIG. 3A in that the intermediate cooler 15 is omitted between the first and second boil-off compressors and between the second and third boil-off compressors included in 13). Do. According to the present invention, the intermediate cooler 15 may or may not be disposed between the boil-off compressors 14 as described above.

In addition, the reliquefaction apparatus 20 which concerns on the modification of this 1st Embodiment illustrated in FIG. 3B is the cold box 21 which heat-exchanges a refrigerant | coolant and boil-off gas, and is heated in this cold box 21 at least partially. Compressing means for compressing the vaporized refrigerant to expand, the expansion means for expanding the compressed refrigerant to lower the temperature.

More specifically, the reliquefaction apparatus 20 according to the modification of the first embodiment illustrated in FIG. 3B includes a cold box 21 for reliquefying the boil-off gas by heat exchange between the refrigerant and the boil-off gas, The first refrigerant gas-liquid separator 22a for separating the partially vaporized refrigerant heated in the cold box 21 into a gaseous refrigerant and a liquid refrigerant, and separated from the first refrigerant gas-liquid separator 22a. A first refrigerant compressor 23a for compressing the gaseous refrigerant, a first refrigerant cooler 24a for cooling the refrigerant compressed in the first refrigerant compressor 23a, and the first refrigerant cooler 24a. The second refrigerant gas-liquid separator 22b for separating the refrigerant cooled in the gas state into a refrigerant in the liquid state and a refrigerant in the liquid state and compressing the gaseous refrigerant separated in the second refrigerant gas-liquid separator 22b. Second refrigerant compressor (23b) and the second refrigerant compressor (2) The first refrigerant pump for supplying the second refrigerant cooler 24b for cooling the refrigerant compressed by 3b) and the liquid refrigerant separated in the first refrigerant gas-liquid separator 22a to the second refrigerant cooler 24b. The second refrigerant pump 26b for supplying the liquid refrigerant separated in the second refrigerant gas-liquid separator 22b to the second refrigerant cooler 24b and the second refrigerant cooler 24b. The third refrigerant gas-liquid separator 22c for separating the refrigerant into gaseous and liquid refrigerants, and the liquid refrigerant separated by the third refrigerant gas-liquid separator 22c to expand the temperature. And a third refrigerant pump 26c for supplying the refrigerant in the liquid state to the refrigerant expansion valve 25 from the third refrigerant gas-liquid separator 22c.

The liquid refrigerant supplied to the second refrigerant cooler 24b from the first and second refrigerant gas-liquid separators 22a and 22b is joined and then supplied from the second refrigerant compressor 23b to the second refrigerant cooler 24b. The second refrigerant cooler 24b may be supplied to the second refrigerant cooler 24b in a mixed state with the gaseous refrigerant. In addition, the gaseous refrigerant separated from the third gas-liquid separator 22c may be mixed with the liquid refrigerant supplied to the refrigerant expansion valve 25 by the third refrigerant pump 26c. In addition, the refrigerant supplied to the refrigerant expansion valve 25 may be configured to exchange heat with the refrigerant in the cryogenic state after expansion while passing through the cold box 21 before expansion.

The reliquefaction apparatus 20 of FIG. 3B is merely an example and does not limit the present invention, and the configuration of the reliquefaction apparatus may be changed as necessary in design.

(Non-explosive mixed refrigerant)

According to the present invention, as the refrigerant circulating in the reliquefaction apparatus 20, a non-explosive mixed refrigerant containing R14 is used, unlike the conventional art. The non-explosive mixed refrigerant formed by mixing a plurality of non-explosive refrigerants has a mixed composition ratio such that the non-explosive mixed refrigerant does not condense even at the liquefaction temperature when re-liquefying the compressed boil-off gas at medium pressure.

The refrigeration cycle using the phase change of the mixed refrigerant is more efficient than the nitrogen gas refrigeration cycle using only nitrogen as a refrigerant. Conventional mixed refrigerants have a problem in safety due to the mixing of explosive refrigerant, but the non-explosive mixed refrigerant of the present invention is high in stability because it is a mixture of non-explosive refrigerant.

With the non-explosive mixed refrigerant of the present invention, it is possible to apply the mixed refrigerant Joule-Thomson refrigeration cycle to the marine LNG reliquefaction apparatus. On the other hand, it has been known to use a mixed refrigerant in an onshore LNG liquefaction plant, but this mixed refrigerant is a hydrocarbon (Hydro-Carbon; hereinafter referred to as "HC") mixed refrigerant and has difficulty in handling. The non-explosive mixed refrigerant of the present invention is composed of argon, hydrofluorocarbon (hereinafter referred to as "HFC") refrigerant, and fluorocarbon refrigerant (hereinafter referred to as "FC") refrigerant. There is no

As the HFC / FC refrigerant, those shown in Table 1 may be used. Table 1 also shows the argon.

Refrigerant number Chemical formula Mole. weight Boiling Point (NBP) (℃) Ar Ar 39.95 -185.9 R14 CF4 88 -128.1 R23 CHF3 70.01 -82.1 R116 CF3CF3 138.01 -78.2 R41 CH3F 34.03 -78.1 R32 CH2F2 52.02 -51.7 R125 CHF2CF3 120.02 -48.1 R143a CH3CF3 84.04 -47.2 R161 CH3CHF2 48.06 -37.1 R218 CF3CF2CF3 188.02 -36.6 R134a CH2FCF3 102.03 -26.1 R152a CH3CHF2 66.05 -24 R227ea CF3CHFCF3 170.03 -15.6 R236fa CF3CH2CF3 152.04 -1.4 R245fa CHF2CH2CF3 134.05 15.1

In addition to the refrigerants shown in Table 1, two or more of these refrigerants may be mixed and used with different refrigerant numbers (R400 and R500 series). These HFC / FC mixed refrigerants are shown in Table 2.

Refrigerant number Mass ratio Mole. weight Boiling Point (NBP) (℃) R410A R32 / 125 (50/50) 72.58 -51.6 R410B R32 / 125 (45/55) 75.57 -51.5 R507 R125 / 143a (50/50) 98.86 -47.1 R407B R32 / 125 / 134a (10/70/20) 102.94 -46.8 R404A R125 / 143a / 134a (44/52/4) 97.6 -46.6 R407A R32 / 125 / 134a (20/40/40) 90.11 -45.2 R407C R32 / 125 / 134a (23/25/52) 86.2 -43.8 R407E R32 / 125 / 134a (25/15/60) 83.78 -42.8 R407D R32 / 125 / 134a (15/15/70) 90.96 -39.4

However, as illustrated in FIGS. 4A and 4B, in the case of the HFC / FC refrigerant, the freezing point is higher than the general temperature of LNG (−163 ° C.) and thus cannot be used as a refrigerant during LNG reliquefaction. However, the inventors pay attention to the fact that the liquefaction (or reliquefaction) temperature rises as the pressure of the natural gas (or evaporated gas) increases, as shown in FIG. 4C, and thus a highly efficient and safe HFC / FC mixed refrigerant. A non-explosive mixed refrigerant has been developed to reliquefy the boil-off gas from LNG storage tanks in offshore structures by Joule-Thomson refrigeration cycle. In other words, according to the present invention, before the reliquefaction of the boil-off gas by pressurizing to a medium pressure of 12 to 45 bara, the boil-off gas at a temperature higher than the temperature of the boil-off liquid reliquefaction at normal pressure, that is, higher than the freezing point of the non-explosive mixed refrigerant Allow reliquefaction of

Non-explosive mixed refrigerant of the present invention, the boiling point is evenly distributed between natural gas liquefaction temperature (or evaporation gas reliquefaction temperature) and room temperature is made by mixing the refrigerant of various components to use a wide phase change section. It is preferable to classify the refrigerants having similar boiling points into five series, and to select one or more components from each series to constitute the non-explosive mixed refrigerant of the present invention. That is, the non-explosive mixed refrigerant of the present invention is made by selecting and mixing at least one component from each of five series.

As shown in FIG. 5, Series I includes Ar having the lowest boiling point among refrigerants, Series II includes R14, Series III includes R23, R116, and R41, and Series IV includes R32, R410A , R410B, R125, R143a, R507, R407B, R404A, R407A, R407C, R407E, R407D, R161, R218, R134a, R152a, and R227ea, and Series V include R236fa and R245fa.

The non-explosive mixed refrigerant of the present invention in which at least one refrigerant is selected from each of these five series has a component and a composition as shown in the following Table 1 in view of ease of supply of refrigerant, cost, and the like. The composition ratio of the non-explosive mixed refrigerant is a temperature difference between the heat exchanger that exchanges heat with the boil-off gas, that is, the hot fluid (ie, the boil-off gas) in the cold box 21 and the low-temperature fluid (that is, the non-explosive mixed refrigerant). It is desirable in terms of efficiency to be determined to be as constant as possible.

Ingredient Composition (% mole) Ar 20 to 55 R14 15 to 30 R23 5 to 15 R410a 10 to 15 R245fa 15 to 20

When the non-explosive mixed refrigerant is used, power consumption, that is, power (kW) can be reduced as compared to when the evaporated gas is reliquefied using nitrogen gas refrigerant as in the prior art, thereby improving reliquefaction efficiency.

More specifically, since the present invention compresses and reliquefies the evaporated gas to a medium pressure of about 12 to 45 bara, which is a relatively high pressure, compared to the evaporated gas pressure used in the conventional reliquefaction apparatus, when reliquefying It is possible to reduce the power required, wherein the pressure range according to the present invention (ie 12 to 45 bara) is determined due to the characteristics of the non-explosive mixed refrigerant of the composition used as the refrigerant in the reliquefaction apparatus. That is, when using the non-explosive mixed refrigerant of the composition, it is possible to maintain the best re-liquefaction efficiency in the reliquefaction apparatus when the boil-off gas preferably has a pressure of about 12 to 45 bara.

In addition, when the pressure of the boil-off gas is 12 bara, the reliquefaction temperature is about -130 ° C, and the temperature of the non-explosive mixed refrigerant is lowered to about -155 ° C in order to cool the boil-off gas to this temperature. Since the non-explosive mixed refrigerant having the composition may cause freezing at -155 ° C. or lower, a refrigeration cycle using the non-explosive mixed refrigerant is difficult to configure when the pressure of the boil-off gas is lower than 12 bara.

In addition, since the critical pressure of the boil-off gas whose main component is methane is about 46 bara, and there is no phase above this critical pressure, the meaning of liquefaction becomes meaningless, and the upper limit of the boil-off gas pressure is preferably set to about 45 bara.

Referring to Figure 6 (a), in the medium pressure, that is, the pressure range of 12 to 45 bara (based on 4.3 ton / h of evaporation gas), the above-mentioned of the present invention compared to the conventional reliquefaction apparatus using a nitrogen gas refrigerant It can be seen that the reliquefaction apparatus using the non-explosive mixed refrigerant having the composition as described above saves power by approximately 10 to 20%.

6 (b) shows the conditions of the reliquefaction apparatus according to the prior art (i.e., when the refrigerant used in the reliquefaction apparatus is nitrogen gas (N2) and the pressure of the boil-off gas supplied to the reliquefaction apparatus is 8 bara). Power requirements and the conditions of the reliquefaction apparatus using the non-explosive mixed refrigerant (NFMR) according to the present invention (i.e., the refrigerant used in the reliquefaction apparatus is a non-explosive mixed refrigerant (NFMR) and evaporation supplied to the reliquefaction apparatus). A graph comparing the power requirement at the pressure of the gas (from 12 to 45 bara) is shown. Referring to Figure 6 (b), compared to the power consumed in the conventional reliquefaction apparatus (refrigeration cycle) using a nitrogen refrigerant, the reliquefaction apparatus of the present invention can be operated with only about 50 to 80% of the power. Able to know. As described above, since the present invention can be operated with considerably less power than in the related art, the generator capacity can be reduced and the generator can be miniaturized.

On the other hand, the reliquefaction apparatus of the present invention uses a Joule Thomson valve as an expansion means of the refrigerant, so that the entire system is simpler and more economical than the conventional N2 compander using an expander. You can get the advantage.

Although not shown in Table 1, the non-explosive mixed refrigerant of the present invention may contain a small amount of non-explosive refrigerant components other than those shown in Table 1.

(Second Embodiment)

FIG. 7A is a block diagram showing a fuel supply system for an offshore structure having a high pressure natural gas injection engine (eg, a ME-GI engine) according to a second embodiment of the present invention. FIG. The fuel supply system of the second embodiment shown in FIG. 7A has a high pressure pump 33 before compressing the boil-off gas to medium pressure and re-liquefying in the reliquefaction apparatus as compared with the fuel supply system of the first embodiment described above. Since they differ from each other only in that they are pre-cooled by heat exchange with LNG supplied to the high-pressure vaporizer 37, the following description focuses on differences from the first embodiment.

As shown in FIG. 7A, the liquefied evaporated gas compressed at high pressure in the high pressure pump 33 is supplied to the reliquefaction apparatus 20 and the heat exchanger 35 to be supplied to the reliquefaction apparatus 20 before being supplied to the high pressure vaporizer 37. Heat exchange at Since the liquefied evaporation gas supplied to the high pressure vaporizer 37 is relatively low temperature compared to the evaporated gas supplied to the reliquefaction apparatus 20, the liquefied evaporation gas supplied to the reliquefaction apparatus 20 passes through the heat exchanger 35. The temperature can be lowered, thereby reducing the reliquefaction energy in the reliquefaction apparatus 20. At the same time, the liquefied evaporation gas supplied to the high pressure vaporizer 37 may be heated while passing through the heat exchanger 35 to reduce the vaporization energy of the high pressure vaporizer 37.

The boil-off gas compressed by the boil-off gas compression unit 13 is supplied to the reliquefaction apparatus 20 through the boil-off gas supply line L2. A heat exchanger 35 is installed in the middle of the boil-off gas supply line L2. As described above, the relatively low-temperature compressed boil-off gas discharged from the high-pressure pump 33 and the compressed high-temperature pump 33 in the heat exchanger 35 are installed. Liquefied evaporation gases exchange heat with each other. The boil-off gas cooled while passing through the heat exchanger 35 is cooled by the refrigerant and re-liquefied while passing through the cold box 21 of the reliquefaction apparatus 20.

(Modification of 2nd Embodiment)

7B shows a fuel supply system according to a modification of the second preferred embodiment of the present invention. The modification of this 2nd Embodiment is partially different from the 2nd Embodiment mentioned above in the structure of the boil-off gas compression part 13 and the reliquefaction apparatus 20 as demonstrated in the modification of 1st Embodiment. Do.

That is, although the boil-off gas compression unit 13 according to the modification of the second embodiment illustrated in FIG. 7B has the same as that shown in FIG. 7A in that it has five boil-off gas compressors 14, the boil-off gas compression 7a in that the intermediate cooler 15 is omitted between the first and second boil-off compressors, and between the second and third boil-off compressors included in section 13. Is different from According to the present invention, the intermediate cooler 15 may or may not be disposed between the boil-off compressors 14 as described above.

In addition, the reliquefaction apparatus 20 which concerns on the modification of this 2nd Embodiment illustrated in FIG. 7B is similar to the reliquefaction apparatus 20 which concerns on the modification of 1st Embodiment illustrated in FIG. A cold box 21 through which heat exchange of the boil-off gas is performed, compression means for compressing a refrigerant at least partially vaporized by heating in the cold box 21, expansion means for expanding the compressed refrigerant to lower the temperature, and gas And a refrigerant gas-liquid separator for separating the refrigerant in the liquid state and the refrigerant in the liquid state.

In particular, the reliquefaction apparatus 20 according to the modification of the second embodiment illustrated in FIG. 7B includes a plurality of refrigerant gas-liquid separators 22a, 22b, and 22c, as in FIG. 2B. The refrigerant gas-liquid separator 22c disposed on the downstream side among the refrigerant gas-liquid separators of the refrigerant gas-liquid separator 22c is supplied after mixing the refrigerant in the gas state and the liquid state in the refrigerant gas-liquid separators 22a and 22b disposed upstream. . The gaseous refrigerant separated in the refrigerant gas-liquid separators 22a and 22b disposed on the upstream side is compressed by the refrigerant compressors 23a and 23b before being supplied to the refrigerant gas-liquid separator 22c disposed on the downstream side. And cooled by the refrigerant coolers 24a and 24b. The liquid refrigerant separated in the refrigerant gas-liquid separators 22a and 22b disposed on the upstream side is more specifically, a gas before the gaseous refrigerant is supplied to the refrigerant gas-liquid separator 22c disposed on the downstream side. The refrigerant in the state is mixed with the gaseous refrigerant before being cooled by the refrigerant cooler 24b.

(Third Embodiment)

8A is a block diagram showing a fuel supply system of an offshore structure having a high pressure natural gas injection engine (for example, a ME-GI engine) according to a third embodiment of the present invention. The fuel supply system of the third embodiment shown in FIG. 8A differs from each other only in that it preheats before compressing the boil-off gas as compared with the fuel supply system of the first embodiment described above, and therefore, in the following description, The differences are explained mainly.

As shown in FIG. 8A, according to the fuel supply system of an offshore structure having a high pressure natural gas injection engine according to a second embodiment of the present invention, the boil-off gas (NBOG) generated and discharged from the liquefied gas storage tank 11 is discharged. Is compressed to a medium pressure of about 12 to 45 bara (absolute pressure) in the boil-off gas compression unit 13, and then the boil-off gas installed upstream of the boil-off gas compression unit 13 before being supplied to the reliquefaction apparatus 20. It is supplied to the preheater 41. The boil-off gas compressed to about 12 to 45 bara in the boil-off gas compression unit 13 and cooled to about 40 ° C. through the intermediate cooler 15 is cryogenically discharged from the liquefied gas storage tank 11 in the boil-off gas preheater 41. It is cooled by heat exchange with the boil-off gas and then supplied to the reliquefaction apparatus 20.

According to the third embodiment, the temperature of the boil-off gas to be supplied to the reliquefaction apparatus 20 can be lowered through the boil-off gas preheater 41, thereby reducing the heat load in the cold box 21. In addition, the cryogenic gas supplied to the boil-off gas compression unit 13 and the boil-off gas having a relatively high temperature compressed by the boil-off gas compression unit 13 are located upstream of the boil-off gas compression unit 13. By exchanging heat in the boil-off gas preheater 41, it is possible to raise the temperature of the boil-off gas supplied to the boil-off gas compression unit and keep the inlet temperature of the boil-off gas compressor (ie, the boil-off gas compressor) constant.

The boil-off gas, which has been compressed by the boil-off gas compression section 13 and passed through the boil-off gas preheater 41, is supplied to the reliquefaction apparatus 20 similarly to the fuel supply system of the first embodiment described above. Subsequently, the liquefied liquefied gas (LBOG) supplied with liquefied energy, that is, cold heat from the reliquefaction apparatus 20 is compressed to a high pressure of about 150 to 400 bara by the high pressure pump 33, and then a high pressure vaporizer ( 37). The boil-off gas vaporized in the high pressure vaporizer 37 is subsequently supplied as fuel to a high pressure natural gas injection engine, such as a ME-GI engine.

(Modification of 3rd Embodiment)

8B shows a fuel supply system according to a modification of the third preferred embodiment of the present invention. The modification of this 3rd Embodiment differs in part from the structure of the reliquefaction apparatus 20 compared with 3rd Embodiment mentioned above.

That is, the reliquefaction apparatus 20 which concerns on the modification of this 3rd embodiment illustrated in FIG. 8B is similar to the reliquefaction apparatus 20 which concerns on the modification of the 1st embodiment illustrated in FIG. A cold box 21 through which heat exchange of the boil-off gas is performed, compression means for compressing a refrigerant at least partially vaporized by heating in the cold box 21, expansion means for expanding the compressed refrigerant to lower the temperature, and gas And a refrigerant gas-liquid separator for separating the refrigerant in the liquid state and the refrigerant in the liquid state.

In particular, the reliquefaction apparatus 20 according to the modification of the third embodiment illustrated in FIG. 8B includes a plurality of refrigerant gas-liquid separators 22a, 22b, and 22c, as in FIG. 2B. The refrigerant gas-liquid separator 22c disposed on the downstream side among the refrigerant gas-liquid separators of the refrigerant gas-liquid separator 22c is supplied after mixing the refrigerant in the gas state and the liquid state in the refrigerant gas-liquid separators 22a and 22b disposed upstream. . The gaseous refrigerant separated in the refrigerant gas-liquid separators 22a and 22b disposed on the upstream side is compressed by the refrigerant compressors 23a and 23b before being supplied to the refrigerant gas-liquid separator 22c disposed on the downstream side. And cooled by the refrigerant coolers 24a and 24b. The liquid refrigerant separated in the refrigerant gas-liquid separators 22a and 22b disposed on the upstream side is more specifically, a gas before the gaseous refrigerant is supplied to the refrigerant gas-liquid separator 22c disposed on the downstream side. The refrigerant in the state is mixed with the gaseous refrigerant before being cooled by the refrigerant cooler 24b.

(Fourth Embodiment)

9A is a block diagram showing a fuel supply system of an offshore structure having a high pressure natural gas injection engine (for example, a ME-GI engine) according to a fourth embodiment of the present invention. The fuel supply system of the fourth embodiment shown in FIG. 9A has a means for treating surplus boil-off gas, that is, a heterogeneous fuel engine (DFDE) and a stable fuel supply, as compared with the fuel supply system of the third embodiment described above. Since the means, that is, the LNG supply line is different from each other in the added, the following description focuses on the differences from the second embodiment.

According to the fuel supply system of the offshore structure having the high pressure natural gas injection engine according to the fourth embodiment of the present invention, when the load of the high pressure natural gas injection engine is reduced or the amount of generated evaporated gas is large, the excess liquefied vaporization gas The LBOG is depressurized through the LBOG expansion valve 51 installed at the LBOG return line L4 branching from the fuel supply line L3 at the rear end of the buffer tank 31, and includes flash gas generated in the depressurization process. After the LBOG is separated into a liquid component (LBOG) and a gas component (flash gas) through a gas-liquid separator, only the liquid component is returned to the storage tank 11 through the LBOG return line (L4).

More specifically, the LBOG containing the flash gas reduced in pressure by the LBOG expansion valve 51 is supplied to the LBOG gas-liquid separator 53 and separated into a liquid component and a gas component, and the gas component separated by the LBOG gas-liquid separator 53. (I.e., flash gas) is supplied as fuel to a heterogeneous fuel engine DFDE that can be installed in an offshore structure for power generation or the like through the fuel gas supply line L6. The pressure of the fuel gas supplied to the heterogeneous fuel engine can be adjusted by a pressure regulating valve installed downstream of the LBOG gas-liquid separator 53 in the middle of the fuel gas supply line L6, and also the fuel gas supply line ( In the fuel gas heater 55 installed in the middle of L6), the temperature of the fuel gas may be heated to a temperature required by the heterogeneous fuel engine. In addition, the liquid component separated in the LBOG gas-liquid separator 53 is returned to the storage tank through the LBOG return line (L4).

At this time, since the fuel gas supply pressure for the heterogeneous fuel engine is generally about 5 to 8 bara, the pressure of the liquid component separated in the LBOG gas-liquid separator 53 may still be higher than the normal pressure. In this case, the liquid component separated from the LBOG gas-liquid separator 53 (i.e., LBOG) is further depressurized through another LBOG expansion valve 52, and is then supplied to another LBOG gas-liquid separator 54 to supply the liquid component ( After separating into LBOG) and a gas component (flash gas), only the liquid component of normal pressure is returned to the storage tank 11 through the LBOG return line L4. The gaseous components separated in another LBOG gas-liquid separator 54 may be consumed by being fed to and combusted with a Gas Combustion Unit (GCU).

On the other hand, when the fuel supplied to the heterogeneous fuel engine is insufficient, the fuel is diverted from the fuel supply line L3 supplying the fuel to the high pressure natural gas injection engine (ie, ME-GI) to supply fuel to the heterogeneous fuel engine (ie, DFDE). Fuel may be additionally supplied to the heterogeneous fuel engine through the branch line L5 connected to the fuel gas supply line L6. The branch line (L5) is provided with a valve for the pressure drop.

In addition, when the boil-off gas reliquefaction apparatus does not operate or the amount of the boil-off gas generated in the storage tank 11 is small, it is stored through the LNG supply pump 57 and the LNG supply line L7 installed in the storage tank 11. Fuel can be supplied by supplying LNG accommodated in the tank 11 to the buffer tank 31.

As such, the heterogeneous fuel engine functions as a flash gas treating means capable of treating flash gas generated from the LBOG on the way back to the storage tank 11 due to the pressure difference.

On the other hand, although not shown in the figure, the gas component separated in the LBOG gas-liquid separator 53 may be supplied to a consumer such as a gas turbine, a boiler or the like instead of a heterogeneous fuel engine, and may be used as fuel. In addition, this gas component can be supplied to and treated by a gas discharge device for releasing natural gas into the atmosphere, or a gas combustion device (for example, a flare tower) for burning in the atmosphere. In this case, a heterogeneous fuel engine, a gas turbine, a boiler, a gas discharge device, a flare tower, and the like are included in the flash gas treating means, and the gas component supplied to the flash gas treating means may be heated in the fuel gas heater 55.

When the boil-off gas liquefied in the reliquefaction apparatus 20 after being compressed to a medium pressure of 12 to 45 bara in the boil-off gas compression unit 13 cannot be consumed by a high-pressure natural gas injection engine such as an ME-GI engine, It is necessary to return the liquefied boil-off gas in the medium pressure state to the storage tank 11. The present inventors, since the pressure of the storage tank 11 is at atmospheric pressure, it is necessary to lower the pressure before supplying the liquefied evaporated gas to the storage tank, but the flash gas is recognized in the process of lowering the pressure, thereby recognizing the flash gas. Invented a fuel supply system having a means for processing. As described above, according to the present invention, since the flash gas treatment means as described above is provided, the boil-off gas supplied to the reliquefaction apparatus can be compressed and supplied to a medium pressure of about 12 to 45 bara, and thus the energy during reliquefaction The consumption can be reduced.

(Modification of 4th Embodiment)

9B shows a fuel supply system according to a modification of the fourth preferred embodiment of the present invention. The modified example of the fourth embodiment is partially different from the above-described fourth embodiment in the configuration of the reliquefaction apparatus 20, and from the evaporative gas compression unit 13 or downstream thereof when excess evaporated gas is generated. It is different from the fourth embodiment in that the excess boil-off gas is treated through a line branching at the side end.

The reliquefaction apparatus 20 according to the modification of the fourth embodiment illustrated in FIG. 9B is similar to the reliquefaction apparatus 20 according to the modification of the first embodiment illustrated in FIG. 2B. A cold box 21 in which heat exchange is performed, compression means for compressing at least partially vaporized refrigerant heated in the cold box 21, expansion means for expanding the compressed refrigerant to lower the temperature, and a gaseous state. Refrigerant gas-liquid separator for separating the refrigerant and the liquid refrigerant.

In particular, the reliquefaction apparatus 20 according to the modification of the fourth embodiment illustrated in FIG. 9B includes a plurality of refrigerant gas-liquid separators 22a, 22b, and 22c as in FIG. 2B. The refrigerant gas-liquid separator 22c disposed on the downstream side among the refrigerant gas-liquid separators of the refrigerant gas-liquid separator 22c is supplied after mixing the refrigerant in the gas state and the liquid state in the refrigerant gas-liquid separators 22a and 22b disposed upstream. . The gaseous refrigerant separated in the refrigerant gas-liquid separators 22a and 22b disposed on the upstream side is compressed by the refrigerant compressors 23a and 23b before being supplied to the refrigerant gas-liquid separator 22c disposed on the downstream side. And cooled by the refrigerant coolers 24a and 24b. The liquid refrigerant separated in the refrigerant gas-liquid separators 22a and 22b disposed on the upstream side is more specifically, a gas before the gaseous refrigerant is supplied to the refrigerant gas-liquid separator 22c disposed on the downstream side. The refrigerant in the state is mixed with the gaseous refrigerant before being cooled by the refrigerant cooler 24b.

In addition, the fuel supply system according to the modification of the fourth embodiment illustrated in FIG. 9B is surplus through the second branch line L8 branching from the boil-off gas compression unit 13 when more boil-off gas is generated than the required amount. It can be configured to supply boil-off gas to a heterogeneous fuel engine (DFDE) for use. In this case, since the temperature of the boil-off gas in the intermediate cooler 15 included in the boil-off gas compression unit 13 is cooled to about 40 ° C., a separate heater or the like for controlling the temperature of the boil-off gas supplied to the different fuel engine is May be omitted.

Alternatively, the excess boil-off gas may be configured to be supplied to the gas turbine through a third branch line L9 branching from the rear end of the boil-off gas compression unit 13. In this case as well, a separate device for controlling the temperature of the boil-off gas supplied to the gas turbine may be omitted.

In addition, the fuel supply system according to the modification of the fourth embodiment illustrated in FIG. 9B is composed of one LBOG expansion valve and one LBOG gas-liquid separator disposed in the LBOG return line L4, respectively, as compared with the fourth embodiment described above. However, as needed, another LBOG expansion valve 52 and LBOG gas-liquid separator 54 may be additionally arranged as necessary in the fourth embodiment.

(Fifth Embodiment)

10A is a block diagram showing a fuel supply system of an offshore structure having a high pressure natural gas injection engine (for example, a ME-GI engine) according to a fifth embodiment of the present invention. The fuel supply system of the fifth embodiment shown in FIG. 10A is more stable than the fuel supply system of the third embodiment described above, that is, a means for treating excess evaporated gas, that is, a gas combustion unit (GCU). They differ from each other in that means for fuel supply, ie LNG supply lines, have been added. In addition, they differ from each other in that they have a means for branching and consuming some of the boil-off gas prior to reliquefaction so as not to generate excess boil-off gas, that is, a heterogeneous fuel engine (DFDE) or a gas turbine. In the following description, the differences from the third embodiment will be mainly described.

According to the fuel supply system of the offshore structure having the high pressure natural gas injection engine according to the fifth embodiment of the present invention, the load of the high pressure natural gas injection engine is reduced or the amount of generated evaporated gas is large, so that the excess liquefied vaporization gas (LBOG) If is expected to occur, the boil-off gas compressed in the boil-off gas compression section 13 or branched through the branch line is used in the boil-off gas consumption means.

That is, the surplus evaporation gas may be configured to be supplied to the heterogeneous fuel engine DFDE through the second branch line L8 branched from the evaporation gas compression unit 13. In this case, since the temperature of the boil-off gas in the intermediate cooler 15 included in the boil-off gas compression unit 13 is cooled to about 40 ° C., a separate heater or the like for controlling the temperature of the boil-off gas supplied to the different fuel engine is May be omitted.

Alternatively, the excess boil-off gas may be configured to be supplied to the gas turbine through a third branch line L9 branching from the rear end of the boil-off gas compression unit 13. In this case as well, a separate device for controlling the temperature of the boil-off gas supplied to the gas turbine may be omitted.

On the other hand, even if the amount of boil-off gas supplied to the reliquefaction apparatus 20 as described above is reduced, if the amount of boil-off gas as the fuel supplied is larger than the amount of boil-off gas required by the high-pressure natural gas injection engine The excess evaporated gas is treated in the same manner as in the above-described fourth embodiment.

That is, the excess evaporated gas is depressurized through the LBOG expansion valve 51 installed in the LBOG return line L4 branching from the fuel supply line L3 at the rear end of the buffer tank 31, and is generated during the depressurization process. The LBOG containing the flash gas is separated into a liquid component (LBOG) and a gas component (flash gas) through the LBOG gas-liquid separator 53, and then only the liquid component is returned to the storage tank 11 through the LBOG return line L4. do. The gas component (that is, flash gas) separated by the LBOG gas-liquid separator 53 is supplied as fuel to the gas combustion unit GCU via the fuel gas supply line L6.

On the other hand, the excess evaporated gas is branched from the fuel supply line (L3) for supplying fuel to the high-pressure natural gas injection engine (ie, ME-GI) and connected to the fuel gas supply line (L6). It can be supplied in addition to the GCU. The branch line (L5) is provided with a valve for the pressure drop.

In addition, as in the fourth embodiment described above, when the boil-off gas reliquefaction apparatus does not operate or the amount of boil-off gas generated in the storage tank 11 is small, the LNG supply pump 57 installed in the storage tank 11 and Fuel may be supplied by supplying LNG contained in the storage tank 11 to the buffer tank 31 through the LNG supply line L7.

In the fourth and fifth embodiments described so far, devices such as DFDE (fourth embodiment) and GCU (fifth embodiment) described as means for treating the generated flash gas, and no flash gas are generated. The devices such as the DFDE (fifth embodiment) and the gas turbine (fifth embodiment), which are described as means for pre-consuming excess evaporated gas before reliquefaction, are all capable of suppressing the generation of flash gas. It can be named as gas suppression means.

(Modification of 5th Embodiment)

10B shows a fuel supply system according to a modification of the fifth preferred embodiment of the present invention. In the modification of the fifth embodiment, the configuration of the reliquefaction apparatus 20 is partially different from that of the fifth embodiment described above.

That is, the reliquefaction apparatus 20 which concerns on the modification of this 5th embodiment illustrated in FIG. 10B is the same as that of the reliquefaction apparatus 20 which concerns on the modification of the 1st embodiment illustrated in FIG. A cold box 21 through which heat exchange of the boil-off gas is performed, compression means for compressing a refrigerant at least partially vaporized by heating in the cold box 21, expansion means for expanding the compressed refrigerant to lower the temperature, and gas And a refrigerant gas-liquid separator for separating the refrigerant in the liquid state and the refrigerant in the liquid state.

In particular, the reliquefaction apparatus 20 according to the modification of the fifth embodiment illustrated in FIG. 10B includes a plurality of refrigerant gas-liquid separators 22a, 22b, and 22c, as in FIG. 2B. The refrigerant gas-liquid separator 22c disposed on the downstream side among the refrigerant gas-liquid separators of the refrigerant gas-liquid separator 22c is supplied after mixing the refrigerant in the gas state and the liquid state in the refrigerant gas-liquid separators 22a and 22b disposed upstream. . The gaseous refrigerant separated in the refrigerant gas-liquid separators 22a and 22b disposed on the upstream side is compressed by the refrigerant compressors 23a and 23b before being supplied to the refrigerant gas-liquid separator 22c disposed on the downstream side. And cooled by the refrigerant coolers 24a and 24b. The liquid refrigerant separated in the refrigerant gas-liquid separators 22a and 22b disposed on the upstream side is more specifically, a gas before the gaseous refrigerant is supplied to the refrigerant gas-liquid separator 22c disposed on the downstream side. The refrigerant in the state is mixed with the gaseous refrigerant before being cooled by the refrigerant cooler 24b.

The fuel supply system of an offshore structure having a high pressure natural gas injection engine according to the first to fifth embodiments of the present invention and its modifications as described above has the following advantages over the prior art.

In general, in order to increase the reliquefaction efficiency of the boil-off gas, it is preferable to compress the boil-off gas to a high pressure. However, conventionally, the liquefied gas is re-liquefied by the reliquefaction apparatus and returned to the storage tank, and since the LNG stored in the storage tank is maintained at atmospheric pressure, the pressure of the reliquefied liquefied liquefied gas is too high to return to the storage tank. In order to prevent flash gas from being generated, the reliquefaction efficiency was low, but the boil-off gas was compressed at a low pressure of about 4 to 8 bara.

In contrast, according to the present invention, since the boil-off gas discharged from the storage tank is used as a fuel in a high-pressure natural gas injection engine, the boil-off gas is compressed and re-liquefied by compressing the boil-off gas to a higher pressure than in the prior art without having to worry about generating flash gas. The liquefaction efficiency can be improved.

Thus, according to the present invention, since the reliquefied evaporated gas is supplied as a fuel to a high-pressure natural gas injection engine, for example, a ME-GI engine, it is not necessary to return the reliquefied evaporated gas to the storage tank for restoring. It is possible to prevent the generation of flash gas, which can be generated upon return to the furnace, and suppresses the generation of flash gas, thereby compressing the pressure of the boil-off gas to a higher pressure than conventionally, that is, 12 to 45 bara before the reliquefaction. To reliquefy. As the evaporated gas is compressed and reliquefied at such a medium pressure, the reliquefaction efficiency by the non-explosive mixed refrigerant can be greatly increased as compared with the use of a nitrogen gas refrigerant as in the prior art. That is, the reliquefaction apparatus of the present invention using a non-explosive mixed refrigerant compared to the conventional nitrogen gas refrigerant can be used to re-liquefy the boil-off gas using a very small amount of energy to supply the engine as fuel.

As the reliquefaction apparatus 20, any structure can be used as long as it can liquefy evaporated gas generated from liquefied gas such as LNG. That is, a reliquefaction system utilizing a non-explosive mixed refrigerant having a configuration as described in the first to fifth embodiments and modifications thereof described above can be used. In addition, a reliquefaction system utilizing a conventionally known nitrogen refrigerant may be used, and for example, those disclosed in WO 2007/117148 and WO 2009/136793 may be used.

According to the fuel gas supply system according to the present invention, during most of the operation of the offshore structure, the liquefied evaporated gas generated in the storage tank is all used as fuel in the high-pressure natural gas injection engine, according to the LBOG return line ( The liquefied gas returned to the storage tank 11 through L4) can be eliminated. The LBOG return line (L4) is used when the towing of offshore structures in the port, when passing through a canal, or when operating at low speed, reduces the fuel consumption of the high pressure natural gas injection engine. Only in extremely exceptional cases, less than the amount, can be used to return the LBOG from the buffer tank 31 to the storage tank 11. In addition, it can be used for the purpose of returning the LBOG remaining in the buffer tank to the storage tank (11) during the failure or maintenance of the buffer tank.

According to this embodiment, since the LBOG can be used in all engines without returning the LBOG to the storage tank during most of the operation of the offshore structure, the returning LBOG itself can be eliminated during that period, and thus the pressure difference during the return of the LBOG. It is possible to remove the flash gas that may occur due to the source. In this specification, the expression "remove flash gas" means that the flash gas is not supplied into the storage tank 11 by consuming the generated flash gas, and the reliquefied evaporated gas is stored in the storage tank 11. It is a concept that includes both preventing the return of the flash gas by preventing the return of the flash gas generated during the return.

In addition, in the present specification, "the fuel consumption of the high pressure natural gas injection engine is more or less than the amount of boil-off gas generated in the storage tank" in the expression "fuel consumption of the high pressure natural gas injection engine" is, the high pressure natural gas injection engine In addition, if there are engines using evaporated gas as fuel in the offshore structure, such as DFDE, gas turbines, etc., the fuel consumption of these engines and the fuel consumption of the high pressure natural gas injection engine should be regarded as added. Of course, if the only engine using the boil-off gas as a fuel is a high pressure natural gas injection engine, it means only the fuel consumption of the high pressure natural gas injection engine.

In the case of the conventionally known reliquefaction apparatus disclosed in WO 2007/117148 and WO 2009/136793, the concept of basically returning the LBOG reliquefied by the reliquefaction apparatus to the LNG storage tank is disclosed. Because of this, the boil-off gas was supercooled to a temperature much lower than the saturation temperature at 4 to 8 bara in accordance with the temperature (approximately -163 ° C) inside the LNG storage tank.

However, according to the fuel supply system of the present invention, since it has a concept of basically supplying the re-liquefied LBOG as a fuel to the high-pressure natural gas injection engine, the evaporated gas is compressed to about 12 to 45 bara, and reliquefaction The reliquefaction temperature in the apparatus is also running the reliquefaction apparatus at a temperature only approximately 1 ° C. below the saturation temperature at that pressure.

According to the present invention, since the reliquefied LBOG is not returned to the storage tank, it is not necessary to consider the temperature and pressure of the LNG stored in the storage tank. In addition, the length of the pipe to transfer the LBOG to the storage tank is relatively long, in the case of the present invention is a relatively short length of the pipe to be transported while maintaining the supercooled state of the LBOG evaporated gas to a temperature too low than the saturation temperature There is no need to overcool it.

Therefore, it is possible to reduce the power consumption of the reliquefaction apparatus by operating the reliquefaction apparatus 20 by setting the liquefaction temperature of the boil-off gas to a temperature slightly lower than the saturation temperature (for example, subcooling only about 1 ° C).

Further, according to the present embodiment, even if the boil-off gas is quenched by only about 1 ° C. below the saturation temperature at the corresponding pressure and liquefied, and then supplied to the buffer tank 31, a high-pressure pump ( As it is pressurized by 33), the saturated LBOG can then remain stable under supercooling due to the pressure increase.

In the offshore structure provided with the conventional reliquefaction apparatus, since the vaporization gas was reliquefied with the intention of returning the vaporization gas to the storage tank, the pressure of the vaporization gas was reduced to 4 to 8 bara to suppress the generation of flash gas upon return. Naturally it was compressed. However, in the fuel gas supply system of the present invention as described above, since all of the vaporized gas is used as a fuel in a high pressure natural gas injection engine after reliquefaction of the boiled gas, the vaporized gas is compressed to a relatively high pressure of about 12 to 45 bara. . This concept can be said to be a novel and progressive concept peculiar to the present invention, which was never conceived before, after re-liquefaction of the boil-off gas and returned to the storage tank.

In addition, in the past, the flash gas is generated by depressurizing the re-liquefied LBOG into the storage tank, and the flash gas is sent back to the reliquefaction apparatus to reduce the efficiency of the reliquefaction apparatus. By using the entire amount of the liquefied LBOG as fuel in the high pressure natural gas injection engine without depressurization (rather than pressurizing), the efficiency of the reliquefaction apparatus can be improved as compared with the conventional art.

Thus, according to the fuel gas supply system of the present invention, since most of the operation period, after the re-liquefaction of the boil off gas is used as fuel in the high-pressure natural gas injection engine, the boil off gas at a relatively high pressure of about 12 to 45 bara It is possible to compress. Accordingly, as described above with reference to FIG. 6, it can be seen that the reliquefaction apparatus of the present invention can operate with only about 50 to 80% of the power compared to the power consumed in the conventional reliquefaction apparatus (refrigeration cycle). have. As described above, since the present invention can be operated with considerably less power than in the related art, the generator capacity can be reduced, so that the generator can be miniaturized and the cost can be reduced.

Moreover, while the conventional reliquefaction apparatus consumes approximately 1 to 1.5 MW of power to operate in the standby state, the reliquefaction apparatus of the present invention can stop the operation of the reliquefaction apparatus for most of the period during the ballast operation. You can save the power consumed by the device. For example, assuming an annual ballast operation of 150 days and using a diesel generator with a fuel consumption of 183 g / kWh for the operation of the reliquefaction unit, an annual HFO of 660 to 923 tonnes can be saved. As of mid-September 2011, Singapore's HFO price is about $ 671 per ton, which can save 0.4 to 0.6 mil USD annually.

In the above description, the fuel supply system and method of the present invention has been described as an example applied to offshore structures such as LNG carriers, but the fuel supply system and method of the present invention is applied to fuel supply for high pressure natural gas injection engines on land. Of course it can.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit and scope of the invention will be.

11: storage tank 13: boil-off gas compression unit
14: boil off gas compressor 15: intermediate cooler
20: reliquefaction apparatus 21: cold box
22: refrigerant gas-liquid separator 23: refrigerant compressor
24: refrigerant cooler 25: refrigerant expansion valve
26 refrigerant pump 31 buffer tank
33: high pressure pump 37: high pressure vaporizer
41: boil-off gas heat exchanger 51, 52: LBOG expansion valve
53, 54: LBOG gas-liquid separator 55: fuel gas heater
57: LNG supply pump L1: boil-off gas discharge line
L2: Evaporative Gas Supply Line L3: Fuel Supply Line
L4: LBOG Return Line L5: Branch Line
L6: Fuel Gas Supply Line L7: LNG Supply Line
L8: second branch line L9: third branch line

Claims (8)

Evaporation gas compression unit for compressing the evaporated gas generated in the storage tank supplied from the storage tank, a reliquefaction apparatus for liquefied by receiving the evaporated gas compressed in the evaporation gas compression unit, liquefied evaporation gas liquefied in the reliquefaction apparatus A system for supplying fuel to a high pressure natural gas injection engine, including a high pressure pump for compressing the gas and a high pressure vaporizer for vaporizing the liquefied evaporated gas compressed in the high pressure pump,
A heat exchanger that cools the evaporated gas by heat-exchanging the evaporated gas compressed by the boil-off gas compression unit and the liquefied evaporated gas compressed by the high pressure pump, and supplies the liquefied evaporated gas to the high-pressure vaporizer. Include,
The reliquefaction apparatus includes a cold box in which heat exchange between a refrigerant and an evaporation gas is performed, compression means for compressing the refrigerant heated in the cold box, expansion means for expanding the compressed refrigerant to lower the temperature, and a gaseous refrigerant. And a refrigerant gas-liquid separator for separating the refrigerant in the liquid state. The method according to claim 1,
The fuel supply system for a high-pressure natural gas injection engine, characterized in that it further comprises a buffer tank for receiving the cooled and liquefied liquefied evaporation gas from the reliquefaction apparatus to separate the gas component and supply only the liquid component to the high pressure pump. The method according to claim 1,
The boil-off gas compression unit includes at least one boil-off gas compressor for compressing the boil-off gas, and at least one intermediate cooler for cooling the boil-off gas whose temperature has risen while being compressed by the boil-off gas compressor. Fuel supply system. The method according to claim 1,
The boil-off gas generated and discharged from the storage tank is compressed to 12 to 45 bara (absolute pressure) in the boil-off gas compression unit and then supplied to the reliquefaction apparatus. . The method according to claim 1,
The reliquefaction apparatus includes a plurality of refrigerant gas-liquid separators, and among the plurality of refrigerant gas-liquid separators, the refrigerant gas-liquid separator disposed at the downstream side is a gaseous refrigerant and a liquid state separated from the refrigerant gas-liquid separator disposed upstream. The fuel supply system for a high-pressure natural gas injection engine, characterized in that the refrigerant is supplied after mixing again. The method according to claim 5,
The gaseous refrigerant separated from the refrigerant gas-liquid separator disposed upstream of the plurality of refrigerant gas-liquid separators is compressed by the refrigerant compressor and cooled by the refrigerant cooler before being supplied to the refrigerant gas-liquid separator disposed most downstream. A fuel supply system for a high pressure natural gas injection engine, characterized in that through. Evaporated gas generated in the storage tank for storing liquefied gas is discharged from the storage tank and compressed, liquefied compressed evaporated gas in the reliquefaction apparatus, compressed liquefied liquefied liquefied gas to high pressure and then vaporized by high pressure natural gas As a fuel supply method for supplying fuel to an injection engine,
The reliquefaction apparatus includes a cold box in which heat exchange between a refrigerant and an evaporation gas is performed, compression means for compressing the refrigerant heated in the cold box, expansion means for expanding the compressed refrigerant to lower the temperature, and a gaseous refrigerant. And a plurality of refrigerant gas-liquid separators for separating a refrigerant in a liquid state,
High-pressure natural gas, characterized in that the refrigerant gas-liquid separator disposed on the downstream side of the plurality of refrigerant gas-liquid separator is supplied after mixing the refrigerant in the gas state and the liquid refrigerant in the refrigerant gas-liquid separator disposed upstream Fuel supply method for injection engines. The method of claim 7,
For high pressure natural gas injection engines, the energy for liquefying evaporated gas is reduced by recovering and using the liquefied energy of the liquefied evaporation gas by heat-exchanging the evaporated gas before liquefaction and the liquefied evaporation gas before vaporization. Fueling method.

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