KR20120107832A - System and method for supplying fuel for high pressure natural gas injection engine - Google Patents

Abstract

PURPOSE: A fuel supply system and method for a high-pressure natural gas injection engine is provided to reduce power of a high pressure pump as LBOG(liquefied boil-off gas) compressed at middle pressure is compressed at high pressure. CONSTITUTION: A fuel supply system and method for a high-pressure natural gas injection engine comprises a BOG(boil-off gas) compression unit(13), a re-liquefying device(20), a buffer tank(31), a high pressure pump(33), and a high pressure vaporizer(37). The BOG compression unit is supplied with BOG from a storage tank(11), and compresses the BOG at 12-45 bar. The re-liquefying device liquefies the compressed BOG. The buffer tank segregates a gaseous component and a liquid component from the liquefied BOG. The high pressure pump compresses the liquid component. The high pressure vaporizer supplies fuel to the high-pressure natural gas injection engine by vaporizing the compressed liquid component. The liquid component supplied from the high pressure pump comprises 12-45 bar pressure.

Description

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

The present invention relates to a fuel supply system and method for a high pressure natural gas injection engine, and more particularly, to an evaporation gas generated from a liquefied natural gas storage tank in a marine structure using a high pressure natural gas injection engine, such as a ME-GI engine. The present invention relates to a fuel supply system and a method of compressing and re-liquefying to medium pressure, and then compressing and vaporizing to high pressure natural gas injection engine.

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 equipped with storage tanks for storing liquefied gas in cryogenic conditions include vessels such as LNG Regasification Vessels, 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. Supplied to a reliquefaction apparatus for use in Korea (Detailed description of Korean Patent Publication No. 10-2006-0123675 describes compression to about 6.8 bara, Korean Patent Publication No. 10-2001-0089142 (corresponding US Patent US 6,530,241) In the detailed description of compression to 4.5 bara is described). 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.

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 a reliquefaction apparatus for reliquefying boil-off gas, nitrogen disclosed in International Patent Publications WO 2007/117148, WO 2009/136793, Korean Patent Publication No. 2006-0123675, Korean Patent Publication No. 2001-0089142, and the like. Refrigeration cycles, mixed refrigerant cycles, and the like have been used. As described above, in such a conventional boil-off gas reliquefaction apparatus, when re-liquefying the boil-off gas, it is generally pressurized at about 4 to 8 bara to reliquefy, and in the art, it is technically reasonable to pressurize more than that. There was widespread perception that they could not. The reason for this is that when the liquefied evaporated gas is reliquefied at a high pressure, when the vaporized gas is later returned to the tank, the pressure is lowered near the normal pressure, so that a lot of flash gas (evaporated gas) is generated.

On the other hand, the nitrogen refrigeration cycle has a problem of low liquefaction efficiency using nitrogen gas (N ₂ ) as the refrigerant, and the mixed refrigerant cycle has a problem of low stability because it uses a refrigerant in which nitrogen and hydrocarbon gas are mixed as the refrigerant. .

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. However, this reliquefaction method is still widely used.

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, using the boil-off gas generated from the liquefied natural gas storage tank as a fuel of a high-pressure natural gas injection engine, for example, ME-GI engine, in the liquefied natural gas storage tank It is to provide a fuel supply system and method that can be supplied to a high pressure natural gas injection engine by compressing and evaporating the generated evaporated gas to medium pressure, and then to high pressure.

Applicant, instead of supplying fuel by the compression of the gas proposed by MAN B & W as a method of supplying fuel to a high-pressure gas injection engine, the fuel (LNG) is compressed (pumped) with a high-pressure pump and then vaporized The company developed the technology to be supplied to Korea and filed it to Korea as of May 8, 2007 (Patent Application No. 10-2007-0044727), and this technology has received great response from ship owners and MAN B & W.

Hamworthy subsequently filed a slight modification of the applicant's technology as filed in WO 2009/136793. However, even after such a technology has been developed, the industry is concerned about the generation of flash gas upon return to the tank after reliquefaction, so the compression range during reliquefaction of heavy gas is a low pressure range (4 to 8 bara) and a higher pressure. The compression of the boil off gas was not considered at all.

After the development of the basic technology of the high pressure pumping of LNG, in the process of developing the technology of using the boil-off gas generated in the LNG storage tank as fuel in the practical application of this technology, 4 to 8 Unlike conventional reliquefaction that compresses and reliquefies to bara, reliquefaction under pressure (12 to 45 bara) in a medium pressure range with a higher pressure than conventional reliquefaction and supplying it with a high pressure pump is required for reliquefaction. It has been found that the energy is significantly reduced, and this finding is the basis for completing the present invention.

In addition, according to the present invention, in addition to the significant reduction in the reliquefaction energy, the power consumption of the high-pressure pump for compressing the LNG pressurized to a high pressure after the reliquefaction is also reduced, and further pressurized by the high-pressure pump after reliquefaction Therefore, it has been found that there is an advantage such as the need for subcooling (subcooling) as in the prior art.

The problems of the invention as described above and the effects thereof are those disclosed for the first time in the present invention.

According to an aspect of the present invention for achieving the above object, a system for supplying a fuel to a high-pressure natural gas injection engine, the evaporation gas for receiving and compressing the evaporated gas generated in the storage tank for storing the liquefied gas from the storage tank A compression unit; A reliquefaction apparatus for liquefying the boil-off gas compressed by the boil-off gas compression unit; A buffer tank for receiving gaseous liquefied gas from the reliquefaction apparatus to separate gaseous and liquid components; A high pressure pump receiving and compressing a liquid component from the buffer tank; A high pressure vaporizer for vaporizing the liquid component compressed by the high pressure pump to supply the high pressure natural gas injection engine; The liquid component supplied to the high pressure pump in the buffer tank is provided with a fuel supply system for a high pressure natural gas injection engine, characterized in that having a pressure of 12 to 45 bara (absolute pressure).

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 reliquefaction apparatus includes a cold box for reliquefying the boil-off gas compressed and supplied from the boil-off gas compression unit by heat exchange between the refrigerant and the boil-off gas, and a refrigerant heated in the cold box and partially vaporized. A refrigerant gas-liquid separator for separating a refrigerant into a liquid refrigerant, a refrigerant compressor for compressing a gaseous refrigerant separated from the refrigerant gas-liquid separator, a refrigerant cooler for cooling the refrigerant compressed in the refrigerant compressor, and And a refrigerant expansion valve for lowering a temperature by expanding the refrigerant cooled in the refrigerant cooler after being compressed by the refrigerant compressor, and a refrigerant pump for supplying the liquid refrigerant separated from the refrigerant gas-liquid separator to the refrigerant expansion valve. desirable.

The fuel supply system returns a portion of the boil-off gas supplied from the buffer tank to the high-pressure pump when the load of the high-pressure natural gas injection engine decreases or the amount of the boil-off gas generated in the storage tank is large. It is preferable to include an LBOG return line.

The fuel supply system preferably includes an LBOG expansion valve installed at the LBOG return line to reduce the liquefied boil-off gas.

The fuel supply system preferably includes an LBOG gas-liquid separator for separating the vaporized gas including the flash gas generated in the depressurization process into a liquid component and a gas component to return only the liquid component to the storage tank.

The fuel supply system may supply LNG contained in the storage tank to the buffer tank when the reliquefaction apparatus is not operated or the amount of boil-off gas generated in the storage tank is less than the consumption of the high pressure natural gas injection engine. It is preferable to include an LNG supply pump and an LNG supply line installed to be able to.

According to another aspect of the present invention, a method for supplying fuel to a high pressure natural gas injection engine, comprising the steps of: compressing the evaporated gas generated in the storage tank from the storage tank; Cooling and re-liquefying the compressed boil-off gas; Separating the reliquefied boil-off gas into a gas component and a liquid component; Compressing the separated liquid component at a high pressure and then vaporizing it to supply the fuel to the high pressure natural gas injection engine; It includes, and the separated liquid component is provided with a fuel supply method for a high pressure natural gas injection engine, characterized in that having a pressure of 12 to 45 bara.

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. Further, before compressing the boil-off gas generated in the storage tank for storing the liquefied gas, the heat-exchanged with the compressed boil-off gas or the nitrogen refrigerant heated in the nitrogen refrigeration cycle of the reliquefaction apparatus preheats the boil-off gas generated in the storage tank. It is preferable. Such cold heat recovery and preheating of the boil-off gas are disclosed in International Patent Publications WO 2007/117148, WO 2009/136793, Korean Patent Publication No. 2006-0123675, and Korean Patent Registration No. 0929250. Can be used. In the present invention, the cooling heat recovery from the liquefied evaporation gas is described, but when the amount of liquefied evaporation gas is less than the fuel required in the high pressure natural gas injection engine, it is necessary to use LNG stored in the LNG storage tank as fuel, in this case The cold heat may be recovered from the LNG supplied from the LNG storage tank.

Examples of the offshore structures include vessels such as LNG RVs, structures such as LNG FSRUs, and LNG FPSOs, in addition to liquefied gas carriers.

The fuel supply method is characterized in that it includes a time for supplying all the liquefied evaporation gas to the high pressure natural gas injection engine during the fuel supply. In other words, during the operation of offshore structures, the amount of fuel required by the high pressure natural gas injection engine is more than the amount of boil-off gas generated in the LNG storage tank for a considerable period of time. By supplying the engine, it is possible to solve the problem of flash gas generated by returning the liquefied evaporation gas to the LNG storage tank.

In still another aspect of the present invention, when the amount of fuel required by the high-pressure natural gas injection engine is greater than or equal to the amount of boil-off gas generated in the LNG storage tank during the operation of the offshore structure, all or a substantial portion of the liquefied evaporation gas may be It is characterized in that the supply to the natural gas injection engine. At this time, the insufficient fuel may use LNG stored in the LNG storage tank as fuel.

According to the present invention, the evaporated gas generated from the liquefied natural gas storage tank is used as a fuel of a high-pressure natural gas injection engine, for example, a ME-GI engine, but the evaporated gas generated from the liquefied natural gas storage tank is compressed to medium pressure and reliquefied. Next, a fuel supply system and method can be provided that can be compressed to high pressure and vaporized to supply a high pressure natural gas injection engine.

According to the fuel supply method for the high-pressure natural gas injection engine of the present invention, instead of compressing the boil-off gas to a low pressure of about 4 to 8 bara of the conventional can be compressed to a medium pressure of about 12 to 45 bara and then re-liquefied, As the pressure of the boil-off gas is increased, the liquefied energy is reduced, thereby reducing the liquefied energy required for reliquefaction.

In addition, according to the fuel supply method for the high-pressure natural gas injection engine of the present invention, since the pressure of the boil-off gas during reliquefaction is higher than the conventional pressure, the liquefied point of the boil-off gas rises and the thermal stress received from the heat exchanger for re-liquefaction This reduces and reduces the heat duty of the high pressure vaporizer, thereby reducing the size of the equipment.

In addition, since the liquefied evaporation gas in a pressurized state at a medium pressure is compressed to high pressure, the power of the high pressure pump is also reduced.

In addition, according to the fuel supply method for the high-pressure natural gas injection engine of the present invention, even in the refrigerant of the reliquefaction apparatus for reliquefaction of the boil-off gas, by using a non-explosive mixed refrigerant is more efficient than the conventional nitrogen refrigeration cycle, conventional mixing Safer reliquefaction is possible than a refrigerant cycle.

The fuel supply method includes a time for supplying all of the liquefied evaporation gas to the high pressure natural gas injection engine during operation of the high pressure natural gas injection engine. In other words, during the operation of offshore structures, the amount of fuel required by the high pressure natural gas injection engine is greater than the amount of boil-off gas generated in the LNG storage tank for a considerable period of time. By supplying the injection engine, it is possible to solve the problem of flash gas generated by returning the liquefied evaporation gas to the LNG storage tank. In addition, in order to reduce the flash gas generated when the liquefied evaporation gas is returned to the LNG storage tank as in the prior art, the energy consumption due to supercooling can be significantly reduced. In the case of a conventional Hamworthy Mark III reliquefaction apparatus (as described in WO 2007/117148), the evaporation gas is pressurized to 8 bara to liquefy to -159 ° C. At this time, since the saturation temperature of the boil-off gas is about -149.5 ° C, about 9-10 ° C is supercooled. This degree of supercooling is required to prevent the generation of flash gas when the liquefied evaporation gas is returned to the LNG storage tank. However, in the present invention, since the liquefied evaporated gas is pressurized by the high pressure pump in the process of supplying the fuel to the high pressure natural gas injection engine, the saturated LBOG may be stably maintained after the supercooled state due to the increased pressure. Therefore, in the present invention, there is an advantage in that the liquefied evaporation gas may be liquefied by subcooling only about 0.5 to 3 ° C, preferably about 1 ° C, than the saturation temperature at the corresponding pressure, and then supplied as fuel.

In addition, according to the fuel supply method for the high-pressure natural gas injection engine of the present invention, if necessary, a heterogeneous fuel engine (DFDE) is mounted to supply the high-pressure natural gas injection engine and the remaining fuel or flash gas generated during decompression of the heterogeneous fuel engine Can be consumed as fuel. In other words, the boil-off gas in excess of the fuel required by the high-pressure natural gas injection engine can be used in the DFDE by compressing directly from the LNG storage tank to about 4 ~ 8 bara without undergoing the reliquefaction process by the medium pressure according to the present invention.

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;
6a to 6c are for comparing the power consumption when using the nitrogen gas refrigeration cycle in the reliquefaction apparatus of the boil-off gas, when using a non-explosive mixed refrigerant refrigeration cycle, and when using a Single Mixed Refrigerant (SMR) refrigeration cycle Graphs,
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 block diagram showing a fuel supply system for a high pressure natural gas injection engine according to a fifth embodiment of the present invention;
10B is a block 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; and
11 is a configuration diagram showing a fuel supply system for a high pressure natural gas injection engine according to a sixth 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 supply method of the present invention, the boil-off gas generated in the storage tank, that is, NBOG is supplied to the boil-off gas compressor and compressed to medium pressure of about 12 to 45 bara, and then the medium pressure BOG is mixed refrigerant, for example, non-explosive mixing. It is supplied to a re-liquefaction apparatus using a refrigerant (Non Flammable Mixed Refrigerant), SMR (Single Mixed Refrigerant), or nitrogen as a 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.

The reliquefaction after compression in the medium pressure range is conventional in both the case of using a nitrogen refrigerant as in FIGS. 6A and 6B, the use of a non-explosive mixed refrigerant, and the use of SMR as in FIG. 6C. Significant re-liquefaction energy savings compared to low pressure reliquefaction.

6A and 6B show data obtained using a Hysys process model (manufactured by Aspentech). The results show that Hamworthy's Mark III reliquefaction unit (technology described in WO 2007/117148), which uses nitrogen gas as a refrigerant, requires the power required for reliquefaction when the pressure of the boil-off compressor is 8 bara. While the pressure is about 2,776 kPa, the pressure of the boil-off gas compressor rises to 12 bara and rapidly decreases to 2,500 kPa. At pressures above 12 bara, the required power for reliquefaction is gradually reduced.

The graph shown in FIG. 6C shows a change in power required when a hydrocarbon-based SMR is used as the refrigerant. Looking at the results, it can be seen that even when using the SMR as the refrigerant, the power required for reliquefaction is rapidly reduced when the pressure of the boil-off gas compressor is 12 bara compared to the pressure of the boil-off gas compressor is 8 bara. At pressures above 12 bara, the required power for reliquefaction is gradually reduced.

The composition of SMR was adjusted as shown in Table 1 below to optimize efficiency for each liquefaction pressure.

Refrigerant Composition (mol%) 8bara 12bara 30bara 45 bara Nitrogen 11.91 5.55 0.00 0.00 Methane 45.11 48.54 45.81 36.63 Ethane 17.68 18.66 22.84 30.74 Propane 10.57 11.30 13.70 13.05 i-Pentane 14.74 15.95 17.65 19.58

In the case of the reliquefaction apparatus using the non-explosive mixed refrigerant (NFMR, the composition of Table 4) described in the present invention, it can be seen that the energy required for reliquefaction is further reduced compared to the case of using the nitrogen gas refrigerant. .

In the present invention, the pressure range of the boil-off gas is preferably a medium pressure range, that is, 12 bara to 45 bara. Below 12 bara, it is not desirable to reduce the power required for reliquefaction. In addition, when it exceeds 45 bara, compared with the power required for pressurization of the boil-off gas, the energy saving required for reliquefaction is not large, which is not preferable.

(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 including R14 may be 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 safety 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 2 may be used. Table 2 shows argon together.

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 2, 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 3.

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 4 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 In particular, when the non-explosive mixed refrigerant of the above composition is used, the reliquefaction efficiency in the reliquefaction apparatus is best when the evaporated gas has a pressure of about 12 to 45 bara. I can keep it.

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, in the case of exceeding 45 bara, it is not preferable because the liquefied energy to be reduced is not large compared to the increase in the power required for pressurization of the boil-off gas.

Referring to FIG. 6A, the present invention is characterized by a medium pressure, that is, a pressure range of 12 to 45 bara (based on 4.3 ton / h of evaporating gas), so that both nitrogen gas refrigerants and non-explosive mixed refrigerants are effective. Compared to the reliquefaction apparatus used, it can be seen that the reliquefaction apparatus using the non-explosive mixed refrigerant having the composition as described above of the present invention further reduces power by approximately 10 to 20%.

6B shows the power requirement in 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). The conditions of the reliquefaction apparatus using the non-explosive mixed refrigerant (NFMR) according to the present invention (ie, the refrigerant used in the reliquefaction apparatus is a non-explosive mixed refrigerant (NFMR) and the pressure of the boil-off gas supplied to the reliquefaction apparatus is A graph comparing the power requirements (in the case of 12 to 45 bara) is shown. Referring to FIG. 6B, 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) using nitrogen refrigerant. 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 2, 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 2.

(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 is more stable than the fuel gas supply system of the third embodiment described above, that is, surplus boil-off gas consumption means for treating surplus boil-off gas, that is, a heterogeneous fuel engine (DFDE) or the like. Since the means for supplying fuel, that is, the LNG supply line is different from each other, the following description focuses on differences from the second embodiment.

In this case, the excess evaporation gas means more evaporation gas than the amount of liquefied evaporation gas required by the high-pressure gas injection engine. If excess evaporated gas is generated, the amount of generated evaporated gas is high even if the high-pressure gas injection engine is in operation, or if the high-pressure gas injection engine operates at low speed or does not operate (for example, when entering a port or opening a canal). May occur).

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, 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 surplus boil-off gas consuming means, i.e., a heterogeneous fuel engine DFDE, which can be installed in the 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), the liquid component of normal pressure is returned to the storage tank 11 through the LBOG return line L4. The gas component separated in another LBOG gas-liquid separator 54 may be consumed by being supplied to and combusted by a gas combustion unit (GCU) as another surplus boil-off gas consumption means.

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. At this time, the heterogeneous fuel engine, gas turbine, boiler, gas discharge device or flare tower is included in the surplus evaporative gas consumption means (flash gas processing means), the gas component supplied to such surplus evaporative gas consumption means is a 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. For example, the present inventors, since the pressure of the storage tank 11 is a normal pressure state, it is necessary to lower the pressure before supplying the liquefied evaporated gas to the storage tank, but recognizes that flash gas is generated in the process of lowering the pressure. A fuel supply system with means capable of treating flash gas, i.e., excess evaporative gas consumption means, has been invented. As such, according to the present invention, since a means capable of treating the flash gas as described above, that is, an excess evaporation gas consumption means is provided, the evaporated gas supplied to the reliquefaction apparatus is compressed to a medium pressure of about 12 to 45 bara. Can be supplied, thereby reducing the energy consumption of reliquefaction.

(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 and use the boil-off gas to a different fuel engine (DFDE) as a surplus boil-off gas consumption means. 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 surplus evaporated gas may be configured to be supplied to the gas turbine as another surplus evaporated gas consumption means through a third branch line L9 branching from the rear end of the evaporated 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, ie, a means for consuming excess evaporated gas, that is, a gas combustion unit (GCU) or the like. 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) ) Is expected to occur, the evaporated gas compressed in the boil-off gas compression section 13 is branched through the branch line and used in the excess boil-off gas consumption means.

That is, it may be configured to supply and use the surplus evaporated gas to the heterologous fuel engine DFDE as the surplus evaporated gas consumption means through the second branch line L8 branched from the evaporated 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 surplus evaporated gas may be configured to be supplied to the gas turbine as another surplus evaporated gas consumption means through a third branch line L9 branching from the rear end of the evaporated 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. After 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, the liquid component is returned to the storage tank 11 through the LBOG return line L4. . The gas component (i.e., flash gas) separated in the LBOG gas-liquid separator 53 is supplied as fuel to the gas combustion unit GCU as the surplus boil-off gas consumption means 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. In addition, since these apparatuses can consume surplus evaporative gas more than the quantity of fuel required by a high pressure gas injection engine, it can also be named as a surplus evaporative gas consumption 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.

(Sixth Embodiment)

FIG. 11 is a configuration diagram showing a fuel supply system for an offshore structure having a high pressure natural gas injection engine (for example, a ME-GI engine) according to a sixth embodiment of the present invention. The fuel supply system of the sixth embodiment shown in FIG. 11 is different from each other in that a recondenser is used in place of the buffer tank included in the fuel supply systems of the first to fifth embodiments described above.

According to the fuel gas supply system of the offshore structure having the high-pressure natural gas injection engine according to the sixth embodiment of the present invention, the boil-off gas (NBOG) generated and discharged from the liquefied gas storage tank 110, the boil-off gas compression unit ( In 113) is supplied to the reliquefaction apparatus 120 after being compressed to a medium pressure of approximately 12 to 45 bara (absolute pressure). The liquefied liquefied gas (LBOG), which is supplied with liquefied energy, that is, cold heat from the reliquefaction apparatus 120, is compressed to a high pressure of about 150 to 400 bara by the high pressure pump 133, and then, to the high pressure vaporizer 137. Supplied. The boil-off gas vaporized in the high pressure vaporizer 137 is subsequently supplied as fuel to a high pressure natural gas injection engine, such as a ME-GI engine.

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 evaporation of the liquefied gas is continuously performed in the storage tank 110, and in order to maintain the pressure of the evaporated gas at an appropriate level, the evaporated gas is discharged through the evaporated gas discharge line L11 in the storage tank 110. Let's do it.

The discharged boil-off gas is supplied to the boil-off gas compression unit 113 through the boil-off gas discharge line L11. The boil-off gas compressor 113 includes one or more boil-off gas compressors 114. Although not shown, the boil-off gas compressor 113 may include one or more intermediate coolers (not shown) for cooling the boil-off gas whose temperature has risen while being compressed by the boil-off gas compressor 114. In FIG. 11, a three-stage compressed boil-off gas compression unit 113 including three boil-off gas compressors 114 is illustrated.

The boil-off gas compressed by the boil-off gas compression unit 113 is supplied to the reliquefaction apparatus 120 through the boil-off gas supply line L12. The boil-off gas supplied to the reliquefaction apparatus 120 is cooled by the refrigerant and re-liquefied while passing through a cold box of the reliquefaction apparatus 120, that is, the main cryogenic heat exchanger 121.

As the reliquefaction apparatus 120, 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.

The boil-off gas liquefied through heat exchange in the cold box 121 is supplied to the recondenser 131 and temporarily stored. According to the present embodiment, the liquefied liquefied gas and the liquefied gas supplied from the liquefied gas storage tank 110, that is, LNG is temporarily stored in the recondenser 131, and reliquefied from the liquefied gas storage tank 110. By bypassing or condensing some or all of the boil-off gas supplied to the device 120 to the re-condenser 131, the overall system efficiency can be improved by reducing or eliminating the amount of boil-off gas entering the re-liquefaction device 120. have. As described in detail below, the recondenser 131 is directly liquefied in the reliquefaction apparatus 120 and then directly supplied to the recondenser 131 to be temporarily stored in the liquefied evaporation gas and the storage tank 110. Cooling heat from at least one of the liquefied gas (ie, LNG) supplied to 131 is used to recondense some or all of the generated boil-off gas.

Since the recondenser 131 may perform a function of separating gas and liquid components, similarly to the buffer tank in the above-described embodiments, the liquefied gas temporarily stored in the recondenser 131 is separated into a gas and a liquid state, Only the liquefied gas in the liquid state is supplied to the high pressure pump 133 through the fuel supply line L13. The high pressure pump 133 may be provided in plural, for example, two in parallel.

In the high pressure pump 133, the liquefied 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 gas sent from the high pressure pump 133 has a high pressure of about 150 to 400 bara (absolute pressure).

If necessary, a booster pump is provided between the high pressure pump 133 and the recondenser 131 of the fuel supply line L13 to ensure a sufficient net suction head (NPSH) in the high pressure pump 133. 132 may be installed.

In addition, as in the above-described second embodiment, the liquefied gas compressed at high pressure in the high pressure pump 133 is supplied to the reliquefaction apparatus 120 and the heat exchanger before being supplied to the high pressure vaporizer 137. The system may be configured to exchange heat at 135. Since the liquefied gas supplied to the high pressure vaporizer 137 is relatively low temperature compared to the boiled gas supplied to the reliquefaction apparatus 120, the temperature of the boiled gas supplied to the reliquefaction apparatus 120 while passing through the heat exchanger 135. Reducing the liquefaction energy in the reliquefaction apparatus 120 can be reduced. In addition, the liquefied gas supplied to the high pressure vaporizer 137 may be heated while passing through the heat exchanger 135 to reduce the vaporization energy of the high pressure vaporizer 137.

The liquefied evaporated gas recondensed and temporarily stored in the recondenser 131 may be returned to the liquefied gas storage tank 110 through the LBOG return line L14, if necessary. Although not shown in FIG. 11, the LBOG return line L14 may be provided with expansion valves, gas-liquid separators, and the like as the fourth and fifth embodiments and modified examples thereof described with reference to FIGS. 9A to 10B.

However, according to the fuel gas supply system according to the sixth embodiment, during most of the operation of the offshore structure, the vaporized gas generated in the storage tank is liquefied and all are used as fuel in the high pressure natural gas injection engine. Accordingly, the liquefied gas returned to the storage tank 110 through the LBOG return line (L14) can be eliminated. The LBOG return line (L14) is used when the towing of the offshore structure in the port, when passing through the canal, or when operating at low speed, the fuel consumption of the high pressure natural gas injection engine Only in very exceptional cases, less than the amount, can be used to return the LBOG from the recondenser 131 to the storage tank 110. In addition, it may be used for the purpose of returning the LBOG remaining in the recondenser 131 to the storage tank 110 during the failure or maintenance of the recondenser.

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 to the inside of the storage tank 110 by consuming the generated flash gas, and the reliquefied evaporated gas is stored in the storage tank 110. 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.

When the amount of boil-off gas generated in the liquefied gas storage tank 110 is less than the amount of fuel required by the high pressure natural gas injection engine, the LNG contained in the storage tank 110 is directly recondensed through the LNG supply line L17. 131 can be supplied. One point of the LNG supply line L17, that is, the starting point of the LNG supply line L17 located inside the liquefied gas storage tank 110 so that LNG contained in the storage tank 110 can be directly supplied to the recondenser 131. The submersible pump 157 is installed. According to the present embodiment, the internal pressure in the recondenser 131 (or the buffer tank 31 in the first to fifth embodiments and variations thereof) is approximately 12 to 12 in the boil-off gas compression unit 130. Since the pressure is about the same as the pressure of the boil-off gas compressed to a medium pressure of about 45 bara, compressing the liquefied gas stored in the storage tank 110 at a pressure of about normal pressure to the medium pressure only by the submersible pump 157. There may be limitations. Therefore, the booster pump 158 is installed in the middle of the LNG supply line L17, and the pressure inside the recondenser 131 (or buffer tank) is discharged to the outside of the storage tank by the submersible pump 157. It is desirable to compress the pressure to the same level as.

When the amount of boil-off gas generated in the liquefied gas storage tank 110 is greater than the amount of fuel required by the high-pressure natural gas injection engine, it is expected that an excess of liquefied liquefied gas (LBOG) will occur. The boil-off gas in the middle of being compressed or compressed in stages is branched through the boil-off gas branch line L18 and used in the boil-off gas consumption means. As an evaporative gas consumption means, a gas turbine, DFDE, or the like, which can use natural gas at a lower pressure than fuel as a ME-GI engine, may be used.

On the other hand, as described above, the fuel gas supply system according to the present embodiment, to reduce the load of the reliquefaction apparatus 120 or to completely stop the operation of the reliquefaction apparatus to improve the efficiency of the entire system, evaporation, The evaporation gas bypass line (L21) which can be directly supplied to the recondenser 131 by bypassing the reliquefaction apparatus by dividing from the gas supply line (L12) and part or all of the evaporated gas compressed by the evaporation gas compression unit 113 to It may include.

More specifically, the boil-off gas bypass line L21 is preferably branched from the heat exchanger 135 downstream of the boil-off gas supply line L12 and connected to the recondenser 131. If necessary, the pressure control valve 161 may be installed in the boil-off gas bypass line L21 to adjust the pressure of the recondenser 131.

When the amount of boil-off gas generated in the liquefied gas storage tank 110 is less than the amount of fuel required by the high pressure natural gas injection engine, LNG in the storage tank 110 is supplied to the recondenser 131 to compensate for the insufficient fuel amount. In this case, a part of the boil-off gas supplied to the re-liquefaction apparatus may be supplied to the re-condenser 131 through the boil-off gas bypass line (L21), mixed with LNG, and condensed to reduce the load of the re-liquefaction apparatus.

Hereinafter, the operation method using the recondenser 131 when the fuel gas supply system of 6th Embodiment comprised as mentioned above is installed in the LNG carrier, for example is demonstrated with reference to FIG.

Since the fuel gas supply system according to the sixth embodiment includes the recondenser 131, all of the boil-off gas generated in the storage tank 110 is not supplied to the cold box 121 of the reliquefaction apparatus 120. By bypassing at least some of the boil-off gas to the recondenser 131, the load of the energy consuming reliquefaction apparatus can be reduced, or in some cases, the operation of the reliquefaction apparatus can be completely stopped.

When the ballast sails the vessel almost empty and sails, the amount of evaporated gas is relatively small. At this time, since the boil-off gas naturally occurring in the storage tank cannot satisfy the fuel demand in the high-pressure natural gas injection engine, LNG stored in the storage tank 110 is transferred to the recondenser 131 through the LNG supply line L17. Supply directly.

In addition, the boil-off gas discharged from the liquefied gas storage tank 110 is compressed to a medium pressure of about 12 to 45 bara in the boil-off gas compression unit 113 and cooled in the heat exchanger 135, and then the boil-off gas bypass line (L21). Through the total amount is supplied to the recondenser 131.

Since the amount of boil-off gas generated during ballast sailing is small, the generated boil-off gas may be supplied to the total amount of the recondenser 131 to be recondensed. That is, during the ballast operation, by recondensing all the boil-off gas generated in the storage tank in the recondenser 131 for most of the period, it is possible to stop the operation of the reliquefaction apparatus. However, when the high pressure natural gas injection engine is operated at a low speed or stops operating, such as during the towing of offshore structures during ballast operation, the fuel consumption of the high pressure natural gas injection engine may be reduced or significantly reduced. Although all of the gas cannot be recondensed and consumed as fuel, and partially reliquefied in the reliquefaction apparatus, this is a very exceptional case during ballast operation.

Since the LNG supplied to the recondenser 131 through the LNG supply line L17 is in a supercooled state, the boil-off gas supplied through the boil-off gas bypass line L21 is mixed with the supercooled LNG in the recondenser 131. In the process of receiving the cold heat from the LNG can be condensed.

As described above, according to the fuel gas supply system of the present embodiment, all of the evaporated gas generated in the ballast can be recondensed in the recondenser 131 to be used as fuel in the high-pressure natural gas injection engine, thereby storing the tank 110 There is no LBOG returning to).

In addition, since the generated evaporated gas can be processed in the total amount of the recondenser 131, the reliquefaction apparatus 120 that consumes a lot of energy and uses a lot of energy may not be operated at all, thus saving a considerable amount of energy. It becomes possible.

On the other hand, during the laden (Lade) voyage to fill and sail the storage tank 110, the amount of evaporated gas is relatively large. At this time, since all the boil-off gas naturally occurring in the storage tank cannot be processed by the recondenser 131, the re-liquefaction device 120 is operated to re-liquefy the boil-off gas. If necessary, some of the generated boil-off gas may be diverted to the recondenser 131 through the boil-off gas bypass line L21 to reduce energy by reducing the reliquefaction load on the reliquefaction apparatus 120.

It is not efficient to cool the boil-off gas to a sub-cooling temperature lower than the saturation temperature in order to cool the boil-off gas in the subcooled state in the reliquefaction apparatus 120. However, when liquefied by only cooling the evaporated gas to the saturation temperature, there is a risk that the saturated LBOG is heated along the pipe to be heated and vaporized again, so when the liquefied evaporated gas in the reliquefaction apparatus 120, It is preferable to cool to the subcooling temperature at the pressure.

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 120 by setting the liquefaction temperature of the boil-off gas to a temperature slightly lower than the saturation temperature (for example, subcooling only 0.5 to 3 ° C, preferably about 1 ° C). Can be.

At this time, by opening and closing the pressure control valve 161 installed on the boil-off gas bypass line (L21), the cooled boil-off gas through the heat exchange in the heat exchanger 135 can be introduced into the re-condenser to recondenser 131 ) Can be adjusted appropriately.

Further, according to the present embodiment, even if the boil-off gas is subcooled by only about 1 ° C. below the saturation temperature at the corresponding pressure and liquefied, and then supplied to the recondenser 131, the booster pump ( 132) and the high pressure pump 133, the saturated LBOG due to the pressure increase can then be stably maintained in the supercooled state.

The fuel supply system of an offshore structure having a high pressure natural gas injection engine according to the first to sixth 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. The reliquefaction efficiency can be improved irrespective of the refrigerant by compressing the evaporated gas to such a medium pressure and reliquefaction. In particular, the reliquefaction efficiency of the non-explosive mixed refrigerant can be further increased compared to using a nitrogen gas refrigerant. 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 apparatuses 20 and 120, 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 sixth embodiments and modifications thereof described above can be used. In addition, a reliquefaction system utilizing a conventionally known mixed refrigerant or nitrogen refrigerant may be used, for example, International Patent Publications WO 2007/117148 and WO 2009/136793, Korean Patent Publication No. 2006-0123675 Or those disclosed in Korean Patent Laid-Open No. 2001-0089142 or the like may also 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 returning to the storage tank 11 through L4 and L14 can be eliminated. The LBOG return lines (L4, L14) are used to evaporate the fuel consumption of the high-pressure natural gas injection engine from the storage tank, such as when towing offshore structures to dock in ports, when passing through canals, or when operating at low speeds. In exceptional cases less than the amount of gas, the LBOG can be used to return the LBOG from the buffer tank 31 or the recondenser 131 to the storage tanks 11 and 110. In addition, it may be used to return the LBOG remaining in the buffer tank (or recondenser) to the storage tanks 11 and 110 when the buffer tank (or recondenser) is broken or maintained.

According to the present invention, since the LBOG can be used in the entire engine without returning the LBOG to the storage tank during most of the operation of the offshore structure, it is possible to eliminate the returning LBOG itself during that period, so that the pressure difference during the return of the LBOG It is possible to remove the flash gas that may occur due to the source. The expression "remove flash gas or suppress flash gas generation" in this specification means that the flash gas is not supplied into the storage tank 11 by consuming the generated flash gas, and reliquefied. The concept includes all of preventing the generation of flash gas by preventing the evaporated gas from returning to the storage tank 11 and blocking the flash gas generation during the return.

In the case of the conventionally known reliquefaction apparatus disclosed in WO 2007/117148, WO 2009/136793, Korean Patent Publication No. 2006-0123675, Korean Patent Publication No. 2001-0089142, etc., basically, Since the LBOG reliquefied by the reliquefaction unit has a concept of returning to the LNG storage tank, the evaporation gas is lower than the saturation temperature at 4 to 8 bara in accordance with the temperature of the LNG storage tank (approximately -163 ° C). Was supercooled.

For example, Hamworthy's Mark III reliquefaction apparatus (as described in WO 2007/117148) liquefies at -159 [deg.] C. by pressurizing the boil-off gas to 8 bara. At this time, since the saturation temperature of the boil-off gas is about -149.5 ° C, about 9-10 ° C is supercooled. This degree of supercooling is required to prevent the generation of flash gas when the liquefied evaporation gas is returned to the LNG storage tank. However, in the present invention, since it is pressurized by a high pressure pump in the process of supplying the liquefied high pressure natural gas injection engine as a fuel, the saturated LBOG may be stably maintained afterwards due to the increase in pressure. In the present invention, there is an advantage in that the liquefied evaporation gas may be cooled by subcooling only 0.5 to 3 ° C, preferably about 1 ° C, than the saturation temperature at the pressure, and then supplied as fuel. The less subcooling in the reliquefaction apparatus, the greater the savings of reliquefaction energy. For example, the energy required to subcool 1 ° C of the boil-off gas at a temperature of -150 ° C requires an additional 1% of the power required for total reliquefaction.

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, and compresses the boil-off gas to about 12 to 45 bara, The reliquefaction temperature of is also operating the reliquefaction apparatus at a temperature of 0.5 to 3 ° C, preferably about 1 ° C lower than the saturation temperature at the pressure.

According to the invention, there is a low need to consider the temperature and pressure of the LNG stored inside the storage tank since the re-liquefied LBOG is not returned to the storage tank if possible. In addition, the length of the pipe to be transported while maintaining the supercooled state of the LBOG (reliquefaction apparatus (eg, gas-liquid separator) -high pressure pump), compared to the conventional length of the pipe for transferring the LBOG to the storage tank is relatively long The length of the gap) is relatively short, and it is not necessary to subcool the boil-off gas to a temperature that is too lower than the saturation temperature.

That is, during the operation of offshore structures, the amount of fuel required by the high pressure natural gas injection engine is greater than the amount of boil-off gas generated in the LNG storage tank for a considerable period of time. By supplying the natural gas injection engine, it is possible to solve the problem of flash gas generated by returning the liquefied evaporation gas to the LNG storage tank.

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 0.5 to 3 ° C).

In addition, according to the present embodiment, even if the evaporated gas is subcooled by only about 0.5 to 3 ° C. below the saturation temperature at the corresponding pressure, the liquefied gas is supplied to the buffer tank 31. Since it is pressurized by the pump 33, the saturated LBOG due to the pressure increase can then be stably maintained in the supercooled state.

In addition, since the LBOG supplied to the high pressure pump is pressurized in the medium pressure range, there is an advantage that the power when pumping the LBOG with the high pressure pump is also reduced.

In the offshore structure provided with the conventional reliquefaction apparatus, since the evaporation gas was reliquefied with the intention of returning the evaporation gas to the storage tank as described above, the pressure of the evaporation gas was reduced to 4 to suppress the generation of the flash gas upon return. Naturally it was compressed to a low pressure of about 8 bara. 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. 6B, 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, in the conventional reliquefaction apparatus, power of about 1 to 1.5 MW was consumed to operate in the standby state. However, in the case of the present invention, as described in the sixth embodiment, the reliquefaction apparatus is operated for most of the period during the ballast operation. Since it can be stopped, the power consumed by the reliquefaction apparatus can be saved. 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, 110: storage tank 13, 113: boil-off gas compression unit
14, 114: boil-off gas compressor 15: intermediate cooler
20, 120: reliquefaction apparatus 21, 121: cold box
22: refrigerant gas-liquid separator 23: refrigerant compressor
24: refrigerant cooler 25: refrigerant expansion valve
26 refrigerant pump 31 buffer tank
33, 133: high pressure pump 37, 137: 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 131, recondenser
132 booster pump 135 heat exchanger
157: submersible pump 158: booster pump
161: pressure control valve L1, L11: boil-off gas discharge line
L2, L12: Evaporative gas supply line L3, L13: Fuel supply line
L4, L14: LBOG Return Line L5: Branch Line
L6: Fuel gas supply line L7, L17: LNG supply line
L8: second branch line L9: third branch line
L18: Boil off gas branch line L21: Boil off gas bypass line

Claims (8)

A system for supplying fuel to a high pressure natural gas injection engine,
An evaporating gas compression unit configured to compress the evaporated gas generated in the storage tank storing the liquefied gas from the storage tank;
A reliquefaction apparatus for liquefying the boil-off gas compressed by the boil-off gas compression unit;
A buffer tank for receiving gaseous liquefied gas from the reliquefaction apparatus to separate gaseous and liquid components;
A high pressure pump receiving and compressing a liquid component from the buffer tank;
A high pressure vaporizer for vaporizing the liquid component compressed by the high pressure pump to supply the high pressure natural gas injection engine;
And a liquid component supplied to the high pressure pump in the buffer tank has a pressure of 12 to 45 bara (absolute pressure). 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 reliquefaction apparatus includes a cold box for reliquefying the boil-off gas compressed and supplied from the boil-off gas compression unit by heat exchange between the refrigerant and the boil-off gas, and a refrigerant heated in the cold box and partially vaporized. A refrigerant gas-liquid separator for separating a refrigerant into a liquid refrigerant, a refrigerant compressor for compressing a gaseous refrigerant separated from the refrigerant gas-liquid separator, a refrigerant cooler for cooling the refrigerant compressed in the refrigerant compressor, and And a refrigerant expansion valve for lowering the temperature by expanding the refrigerant cooled in the refrigerant cooler after being compressed by the refrigerant compressor, and a refrigerant pump for supplying the refrigerant in the liquid state separated from the refrigerant gas-liquid separator to the refrigerant expansion valve. A fuel supply system for a high pressure natural gas injection engine. The method according to claim 1,
When the load of the high-pressure natural gas injection engine is reduced or the amount of boil-off gas generated in the storage tank is large, it includes an LBOG return line for returning some of the boil-off gas supplied from the buffer tank to the high-pressure pump to the storage tank. A fuel supply system for a high pressure natural gas injection engine, characterized in that. The method of claim 4,
And a LBOG expansion valve installed in the LBOG return line to reduce the liquefied evaporated gas. The method according to claim 5,
A fuel supply system for a high-pressure natural gas injection engine comprising an LBOG gas-liquid separator for separating the evaporated gas including the flash gas generated in the depressurization process into a liquid component and a gas component and returning only the liquid component to the storage tank. . The method according to claim 1,
LNG supply pump installed to supply LNG contained in the storage tank to the buffer tank when the reliquefaction device does not operate or the amount of boil-off gas generated in the storage tank is less than the consumption of the high pressure natural gas injection engine. And LNG supply line for fuel supply system for a high pressure natural gas injection engine comprising a. As a method for supplying fuel to a high pressure natural gas injection engine,
Compressing the evaporated gas generated in the storage tank by discharging it from the storage tank;
Cooling and re-liquefying the compressed boil-off gas;
Separating the reliquefied boil-off gas into a gas component and a liquid component;
Compressing the separated liquid component at a high pressure and then vaporizing it to supply the fuel to the high pressure natural gas injection engine; Including;
The separated liquid component has a pressure of 12 to 45 bara fuel supply method for a high pressure natural gas injection engine, characterized in that.

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