KR101356004B1 - Method for treating boil-off gas for a ship - Google Patents

Abstract

The present invention relates to a method for treating evaporation gas of a vessel allowing evaporation gas to efficiently be used by pressurizing evaporation gas discharged from a storage tank, and using most of them as fuel of a high pressure natural gas spray engine for a vessel and liquefying the rest of them to cold energy of evaporation gas newly discharged from the storage tank to return to the storage tank. According to the present invention, the method for treating evaporation gas of a vessel, which has a storage tank for storing liquefied natural gas and a high pressure natural gas spray engine for using evaporation gas discharged from the storage tank as fuel, comprises: a compressing step of receiving evaporation gas generated in the storage tank to be compressed by a compressor; a supplying step of classifying the evaporation gas compressed in the compressing step to supply a portion of the evaporation gas to the high pressure natural gas spray engine as fuel; and a cooling step of heat exchanging, by a heat exchanger, the rest of the evaporation gas which is not supplied to the high pressure natural gas spray engine as fuel with evaporation gas which is not compressed after being discharged from the storage tank to be cooled.

Description

Process for treating boil off gas {METHOD FOR TREATING BOIL-OFF GAS FOR A SHIP}

The present invention relates to a method for treating boil-off gas of a ship equipped with a high-pressure natural gas injection engine, and more particularly, to evaporate from a storage tank without having to install a reliquefaction device that consumes much energy and excessively requires an initial installation cost. After pressurizing the gas, most of them are used as fuel for the high pressure natural gas injection engine of the ship, and the other part is liquefied by the cold heat of the newly discharged boil-off gas from the storage tank and returned to the storage tank so that the efficient use of the boil-off gas It relates to a method for treating boil off gas.

In recent years, consumption of liquefied gas such as LNG (Liquefied Natural Gas) and LPG (Liquefied Petroleum Gas) has been rapidly increasing worldwide. The liquefied gas is transported in a gaseous state via land or sea gas piping, or is transported to a distant consumer site 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 at a very low temperature (approximately -163 ° C. in the case of LNG), and its volume is significantly reduced compared to when it is in a gaseous state, .

The liquefied gas carrier, such as an LNG carrier, is used to load the liquefied gas with the liquefied gas to the sea and to unload the liquefied gas to the onshore site. For this purpose, a storage tank capable of withstanding the extremely low temperature of the liquefied gas ).

Examples of maritime structures having storage tanks capable of storing liquefied gas at cryogenic temperatures include ships such as LNG RV (Regasification Vessel), LNG FSRU (Floating Storage and Regasification Unit), LNG FPSO (Floating, Production, Storage and off-loading), and the like.

LNG RV is a LNG regasification facility installed on a LNG carrier that can be self-driving and floating. LNG FSRU stores LNG in a storage tank that is unloaded from LNG carriers at sea, away from the land. It is an offshore structure that vaporizes liquefied 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, a vessel is a concept that includes a structure such as LNG FPSO, LNG FSRU, as well as a liquefied gas carrier such as an LNG carrier, an LNG RV, and the like.

Since the liquefaction temperature of natural gas is a cryogenic temperature of about -163 ° C at normal pressure, LNG is evaporated even if its temperature is slightly higher than -163 ° C at normal pressure. For example, in the case of a conventional LNG carrier, the LNG storage tank of the LNG carrier is heat-treated, but since the external heat is continuously transferred to the LNG, LNG is transported by the LNG carrier, The LNG storage tank is constantly vaporized and boil-off gas (BOG) is generated in the LNG storage tank.

The generated evaporation gas increases the pressure in the storage tank and accelerates the flow of the liquefied gas in accordance with the shaking motion of the ship, which may cause a structural problem, so it is necessary to suppress the generation of the evaporation gas.

BACKGROUND ART [0002] Conventionally, in order to suppress and treat evaporation gas in a storage tank of a liquefied gas carrier, a method of discharging evaporation gas to the outside of the storage tank and incinerating it, a method of discharging evaporation gas to the outside of the storage tank, A method of returning to the storage tank after re-liquefying, a method of using evaporation gas as fuel used in a propulsion engine of the ship, a method of suppressing the generation of evaporation gas by keeping the internal pressure of the storage tank high, Have been used in combination.

In the case of a conventional ship equipped with an evaporation gas remelting device, the evaporation gas inside the storage tank is discharged to the outside of the storage tank and re-liquefied through the re-liquefaction device in order to maintain an appropriate pressure of the storage tank. At this time, the discharged evaporated gas is re-liquefied through a heat exchange with a refrigerant cooled at a cryogenic temperature, for example, nitrogen, mixed refrigerant, etc., in a liquefaction device including a refrigeration cycle, and then returned to the storage tank.

In the case of the conventional LNG carriers equipped with the DFDE propulsion system, since the evaporative gas is treated through the evaporation gas compressor and the heating only without the liquefaction facility, and the evaporated gas is consumed by supplying the DFDE as fuel, When the amount of generated gas is less than the amount of generated gas, there is a problem that the evaporation gas must be burned in a gas combustion unit (GCU) or vented to the atmosphere.

Although the conventional Liquefaction Facility and the LNG carrier equipped with the low speed diesel engine can process the BOG through the liquefaction facility, the control of the entire system is complex due to the complexity of operation of the liquefaction device using nitrogen gas, There was a problem that the power was consumed.

As a result, there is a need to continuously research and develop systems and methods for efficiently treating evaporative gases occurring naturally from storage tanks.

Patent Registration No. 10-1106088 (2012.01.18.)

The present invention is to solve the conventional problems as described above, after pressurizing the evaporated gas discharged from the storage tank is mostly used as fuel of the high-pressure natural gas injection engine of the vessel and the other part is newly discharged from the storage tank It is to provide a method of treating a boil-off gas of a vessel to liquefy by cooling heat of the boil-off gas and return to the storage tank, so that the boil-off gas can be efficiently used.

According to an aspect of the present invention for achieving the above object, the evaporation gas treatment of a ship having a storage tank for storing liquefied natural gas, and a high-pressure natural gas injection engine using the evaporated gas discharged from the storage tank as a fuel A method comprising: a compression step of receiving a boil-off gas generated in the storage tank and compressing the same with a compressor; Supplying a portion of the boil-off gas compressed in the compression step to supply a portion of the boil-off gas as fuel to the high-pressure natural gas injection engine; A cooling step of cooling the remaining boil-off gas not supplied as fuel to the high-pressure natural gas injection engine by exchanging heat in the heat-exchanger with the boil-off gas before being compressed from the storage tank; Provided is a method for treating boil-off gas in a ship comprising: a.

In the cooling step, it is preferable that the part of the compressed boil-off gas not supplied to the high-pressure natural gas injection engine is cooled by heat exchange with the boil-off gas discharged from the storage tank and transferred to the compressor.

After the cooling step, it is preferable to further include a return step of returning to the storage tank after lowering the pressure of the boil-off gas cooled in the heat exchanger.

It is preferable that only the liquid component be separated from the evaporated gas which has been reduced in pressure and mixed with the gas liquid, and returned to the storage tank.

It is preferable to further cool the boil-off gas cooled by the heat-exchanger by heat-exchanging with gaseous components of the boil-off gas which have been decompressed to form a gas-liquid mixed state.

The gas component is preferably discharged from the storage tank and joined to the boil-off gas supplied to the compressor.

It is preferable that the said compressor contains a some compression cylinder.

It is preferable to further include a boil-off gas consumption means for receiving and using a compressed boil-off gas through a portion of the plurality of compression cylinders included in the compressor.

The boil-off gas sent to the heat exchanger is preferably boil-off gas compressed through some or all of the plurality of compression cylinders included in the compressor.

It is preferable to further include a forced vaporization step for forcibly vaporizing the liquefied natural gas stored in the storage tank to supply to the compressor.

The vessel includes a compressor line for compressing the boil-off gas generated in the storage tank by the compressor to supply the high-pressure gas injection engine as fuel; A high pressure pump line for compressing LNG contained in the storage tank by a high pressure pump and supplying the high pressure gas injection engine as fuel; .

According to the present invention, after pressurizing the boil-off gas discharged from the storage tank, some of the compressed boil-off gas is supplied as fuel to the high-pressure natural gas injection engine of the ship, and the rest of the compressed boil-off gas is newly discharged from the storage tank and compressed There may be provided a method of treating a boil-off gas of a ship which can be liquefied by cold heat of boil-off gas before returning to a storage tank.

Accordingly, according to the method of treating the boil-off gas of the present invention, it is possible to re-liquefy the boil-off gas generated in the storage tank without installing a re-liquefaction device that consumes a lot of energy and excessively requires an initial installation cost. Energy can be saved.

In addition, according to the method of treating the boil-off gas of the present invention, since all boil-off gas generated when the cargo of the LNG carrier (i.e., LNG) is transported can be used as the fuel of the engine or re-liquefied and returned to the storage tank, the GCU It is possible to reduce the amount of boil-off gas consumed by the back, and to re-liquefy and treat the boil-off gas without using a separate refrigerant such as nitrogen.

In addition, according to the method for treating an evaporation gas of the present invention, since a reliquefaction apparatus using a separate refrigerant (that is, a nitrogen refrigerant refrigeration cycle or a mixed refrigerant refrigeration cycle, etc.) does not need to be installed, an equipment for supplying and storing refrigerant is provided. There is no need to install additional ones, which saves the initial installation and running costs for the entire system.

1 is a schematic configuration diagram showing a marine fuel gas supply system,
2 is a schematic structural diagram showing a boil-off gas treatment system according to a first embodiment of the present invention;
Figure 3 is a schematic configuration diagram showing a boil-off gas treatment system according to a second embodiment of the present invention,
4 is a schematic view showing a state in which a vapor gas processing system according to a first preferred embodiment of the present invention is used together with a fuel gas supply system,
5 and 6 are schematic configuration diagrams showing a boil-off gas treatment system according to a modification of the first preferred embodiment of the present invention.

In general, among the waste gases emitted from vessels, those regulated by the International Maritime Organization are nitrogen oxides (NOx) and sulfur oxides (SOx), and in recent years they have also been trying to regulate the emission of carbon dioxide (CO ₂ ) have. 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.

Accordingly, various methods for reducing nitrogen oxide (NOx) emissions have been introduced to meet these requirements. Of these methods, a high pressure natural gas injection engine for ships such as LNG carriers, for example a MEGI engine, has been developed and used have. The ME-GI engine is seen as an environmentally friendly next-generation engine that can reduce pollutant emissions by 23%, nitrogen compounds 80%, and sulfur compounds 95% or more, compared with diesel engines of the same class.

Such a MEGI engine is a vessel such as an LNG carrier for storing and transporting LNG in a cryogenic storage tank (in this specification, a vessel is an LNG carrier, an LNG RV, etc., as well as a marine plant such as LNG FPSO, LNG FSRU, etc.). In this case, natural gas is used as a fuel, and a high pressure gas supply pressure of about 150 to 400 bara (absolute pressure) is required for the engine depending on the load.

The MEGI engine can be used directly to the propeller for propulsion, for which the MEGI engine consists of a two-stroke engine rotating at low speed. That is, the MEGI engine is a low-speed two-stroke high-pressure natural gas injection engine.

Further, in order to reduce nitrogen oxide emissions, a DF engine (for example, DFDG: Dual Fuel Diesel Generator) which is a mixture of diesel oil and natural gas and used as fuel has been developed and used for propulsion and power generation. The DF engine is an engine that can mix oil and natural gas or use only one selected from oil and natural gas as fuel. The sulfur content in the exhaust gas is smaller than the sulfur content in the fuel, little.

The DF engine does not need to supply fuel gas at the same high pressure as the MEGI engine, and compresses the fuel gas to about several to several tens of bara. The DF engine obtains power by driving the generator by the driving force of the engine, and drives the propulsion motor or operates various devices or equipments by using this electric power.

When supplying natural gas as a fuel, it is not necessary to match the methane in the case of the MEGI engine, but in the case of the DF engine, it is necessary to match the methane.

When the LNG is heated, the methane component having a relatively low liquefaction temperature is preferentially vaporized. Therefore, in the case of the vaporized gas, the methane content is high and can be supplied as fuel to the DF engine as it is. However, in the case of LNG, the methane content is relatively low, which is lower than the methane demanded by the DF engine, and the ratio of the hydrocarbon components (methane, ethane, propane, butane, etc.) It is not suitable to be supplied as fuel to the DF engine.

To regulate methane, the liquefied natural gas can be forcedly vaporized and then cooled to remove liquefied heavy hydrocarbons (HHC), which have a higher liquefaction point than methane. After adjusting the methane, additional methane-regulated natural gas may be added to meet the temperature requirements of the engine.

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.

1 is a configuration diagram illustrating a hybrid fuel supply system according to an embodiment of the present invention. The hybrid fuel supply system of the present invention can be applied to an LNG carrier or the like equipped with, for example, a MEGI engine as a propulsion main engine.

Referring to FIG. 1, a hybrid fuel supply system 100 according to an embodiment of the present invention provides a path for transferring an LNG from a cargo tank 1 to a main engine 3 A fuel supply line 110 and a BOG line 140 providing a path for transferring BOG generated from the storage tank 1 to the main engine 3. In addition, the hybrid fuel supply system 100 using the BOG according to an embodiment of the present invention, LNG through the fuel supply line 110 to the LNG pump (LNG pump; 120) and LNG vaporizer (LNG vaporizer; 130) To the main engine 3 as fuel, and the BOG is compressed by the BOG compressor 150 through the BOG line 140 to be supplied to the main engine 3 as fuel, and from the BOG compressor 150 Surplus BOG is fed to the integrated IGG / GCU system 200.

MEGI engines that can be used as the main engine 3 need to be fueled at a high pressure of approximately 150 to 400 bara (absolute pressure). Therefore, as the LNG pump 120 and the BOG compressor 150 according to the present embodiment, a high-pressure pump and a high-pressure compressor capable of compressing LNG and BOG, respectively, to a pressure required by the MEGI engine are used.

The fuel supply line 110 provides a path for transferring the LNG supplied by the drive of the transfer pump 2 from the storage tank 1 of the LNGC as fuel to the main engine 3, And an LNG vaporizer 130 are installed.

The LNG pump 120 is installed to supply the pumping force necessary for transferring the LNG to the fuel supply line 110. For example, the LNG HP pump (LNG High Pressure pump) may be used. In the present embodiment, .

The LNG vaporizer 130 is installed at the rear end of the LNG pump 120 in the fuel supply line 110 to vaporize the LNG conveyed by the LNG pump 120. In order to vaporize the LNG, Various kinds of heating means may be used for providing heat of vaporization of LNG including heaters as another example. In addition, the LNG vaporizer 130 may be a high pressure vaporizer that can be used at a high pressure for vaporizing the LNG. On the other hand, steam generated from a boiler or the like can be used as the fruit to be circulated and supplied to the fruit circulation line 131, for example.

The BOG line 140 provides a path for transferring the BOG generated naturally from the storage tank 1 to the main engine 3 and is connected to the fuel supply line 110 as in the present embodiment, To the engine 3, or alternatively it may provide a path for supplying the BOG directly to the main engine 3.

The BOG compressor 150 is installed in the BOG line 140 to compress the BOG through the BOG line 140. Although only one BOG compressor 150 is shown in FIG. 1, the BOG compressor is configured such that the two compressors of the same specification are connected in parallel to meet redundancy requirements, as in a conventional fuel supply system. Lt; / RTI > However, in the case where a single BOG compressor 150 is installed in the branch of the redundant BOG line 160 in the BOG line 140 as in the present embodiment, an economical burden due to the installation of the expensive BOG compressor 150, And reduce the burden on the repairer.

The redundant BOG line 160 provides a path for supplying surplus BOG from the BOG compressor 150 to the integrated IGG / GCU system 200, which may include an integrated IGG / GCU system 200 as well as an auxiliary The surplus BOG can be supplied as fuel by an engine or the like.

The integrated IGG / GCU system 200 is an integrated system of IGG (Inert Gas Generator) and GCU (Gas Combustion Unit).

The surplus BOG line 160 and the fuel supply line 110 may be connected to each other by a connection line 170. Thus, the surplus BOG can be used as fuel for the main engine 3 by the connection line 170, or the vaporized LNG can be used as fuel for the integrated IGG / GCU system 200. The connection line 170 may be provided with a heater 180 for heating BOG or vaporized LNG passing therethrough and may be provided with a pressure reduction valve (Pressure Reduction) for reducing excessive pressure by controlling the pressure by BOG or vaporized LNG. (PRV) 190 may be installed. Meanwhile, the heater 180 may be a gas heater using heat of combustion of gas, or various heating means may be used as well as a heat circulation supply unit that provides a heat source for heating by circulation of the heat.

The operation of the hybrid fuel supply system according to the present invention will now be described.

When the pressure in the storage tank 1 is equal to or higher than a predetermined pressure or the amount of generated BOG is large, BOG is compressed by driving the BOG compressor 150 and supplied to the main engine 3 as fuel. When the pressure in the storage tank 1 is lower than the predetermined pressure or the BOG generation amount is small, the LNG pump 120 and the LNG vaporizer 130 are driven to transfer and vaporize the LNG to supply it to the main engine 3 as fuel .

The surplus BOG from the BOG compressor 150 is supplied to the auxiliary IGG / GCU system 200 or the auxiliary engine such as the DF engine through the surplus BOG line 160 to the BOG consuming or storing tank 1 To be used for the purpose of producing an inert gas to be supplied, and further to be used as fuel for an auxiliary engine or the like.

The integrated IGG / GCU system 200 to which the BOG is supplied can consume BOG continuously generated from the storage tank 1 by BOG combustion in the main body 210 and supply the BOG to the storage tank 1 It is also possible to generate a combustion gas as an inert gas.

2 shows a schematic configuration diagram of a boil-off gas treatment system according to a first preferred embodiment of the present invention.

2 shows an example in which the boil-off gas treatment system of the present invention is applied to a high-pressure natural gas injection engine that can use natural gas as a fuel, that is, an LNG carrier equipped with a MEGI engine, but the boil-off gas treatment system of the present invention is liquefied. It can be applied to all kinds of ships equipped with gas storage tanks, such as LNG carriers, LNG RVs, etc., as well as offshore plants such as LNG FPSO, LNG FSRU.

According to the boil-off gas treatment system according to the first embodiment of the present invention, the boil-off gas NBOG generated and discharged from the storage tank 11 storing the liquefied gas is along the boil-off gas supply line L1. It is conveyed and compressed in the compressor 13 and then supplied to a high pressure natural gas injection engine, such as a MEGI engine. The evaporation gas is compressed by the compressor 13 to a high pressure of about 150 to 400 bara and then supplied as fuel to a high pressure natural gas injection engine, such as a MEGI engine.

The storage tank has a sealing and thermal barrier to store liquefied gases such as LNG in cryogenic conditions, but it can not completely block the heat transmitted from the outside. Accordingly, the evaporation of the liquefied gas is continuously performed in the storage tank 11, and the evaporation gas in the storage tank 11 is discharged through the evaporation gas discharge line L1 to maintain the pressure of the evaporation gas at an appropriate level .

A discharge pump (12) is installed in the storage tank (11) to discharge the LNG to the outside of the storage tank, if necessary.

The compressor 13 may include one or more compression cylinders 14 and one or more intercoolers 15 for cooling the evaporated gas as it is being compressed. The compressor 13 may be configured, for example, to compress the evaporation gas to about 400 bara. In Fig. 2, a multi-stage compression compressor 13 including five compression cylinders 14 and five intermediate coolers 15 is illustrated, but the number of compression cylinders and intercoolers can be changed as needed. Further, in addition to the structure in which a plurality of compression cylinders are arranged in one compressor, the structure may be changed to have a structure in which a plurality of compressors are connected in series.

The evaporated gas compressed in the compressor 13 is supplied to the high-pressure natural gas injection engine through the evaporation gas supply line L1. In accordance with the amount of fuel required in the high-pressure natural gas injection engine, Gas injection engine, or may supply only a part of the compressed evaporated gas to the high-pressure natural gas injection engine.

According to the first embodiment of the present invention, when the evaporated gas discharged from the storage tank 11 and compressed by the compressor 13 (that is, the entire evaporated gas discharged from the storage tank) is referred to as a first stream, The first stream of gas may be divided into a second stream and a third stream after compression and the second stream may be supplied as fuel to the high pressure natural gas injection engine and the third stream may be liquefied and returned to the storage tank.

At this time, the second stream is supplied to the high-pressure natural gas injection engine through the evaporation gas supply line L1 and the third stream is returned to the storage tank 11 through the evaporation gas return line L3. A heat exchanger (21) is installed in the evaporation gas return line (L3) so that the third stream of compressed evaporation gas can be cooled and liquefied. The heat exchanger 21 heat exchanges the third stream of the compressed evaporated gas with the first stream of the evaporated gas which is discharged from the storage tank 11 and then supplied to the compressor 13.

Because the flow rate of the first stream of evaporated gas before being compressed is greater than the flow rate of the third stream, the third stream of compressed evaporated gas may be liquefied by receiving cold heat from the first stream of evaporated gas before being compressed. Thus, in the heat exchanger 21, the extremely low temperature evaporated gas immediately after being discharged from the storage tank 11 is exchanged with the evaporated gas in the high pressure state compressed by the compressor 13, thereby cooling and liquefying the evaporated gas in the high pressure state.

The evaporated gas LBOG cooled in the heat exchanger 21 and at least partially liquefied is passed through the expansion valve 22 and is depressurized and supplied to the gas-liquid separator 23 in a vapor-liquid mixed state. The LBOG can be decompressed to approximately atmospheric pressure while passing through the expansion valve 22. The liquefied evaporated gas is separated from the gas and liquid components in the gas-liquid separator 23, and the liquid component, that is, the LNG is transferred to the storage tank 11 through the evaporated gas return line L3, and the gas component, And is then discharged from the storage tank 11 via the evaporation gas recirculation line L5 and joined to the evaporation gas supplied to the compressor 13. [ More specifically, the evaporation gas recycle line L5 extends from the upper end of the gas-liquid separator 23 and is connected to the evaporation gas supply line L1 on the upstream side of the heat exchanger 21.

In the above description, the heat exchanger 21 is provided in the evaporation gas return line L3, but in the heat exchanger 21, the first stream of the evaporation gas being fed through the evaporation gas supply line L1 The heat exchanger 21 is installed in the evaporation gas supply line L1 since heat exchange is performed between the third stream of the evaporation gas being transferred through the evaporation gas return line L3.

The evaporation gas recirculation line L5 may be further provided with another expansion valve 24 so that the gas component discharged from the gas-liquid separator 23 can be decompressed while passing through the expansion valve 24. The third stream of the evaporated gas supplied to the gas-liquid separator 23 after being liquefied in the heat exchanger 21 is heat-exchanged with the gas component separated by the gas-liquid separator 23 and conveyed through the evaporation gas recycle line L5, The evaporator gas recycle line (L5) is equipped with a cooler (25) to further cool the stream. That is, in the cooler 25, the evaporation gas in the high-pressure liquid state is further cooled by the low-pressure ultra-low temperature gaseous natural gas.

Although the cooler 25 has been described as being installed in the evaporative gas recirculation line L5 for convenience of explanation, in the cooler 25 in reality, the third stream of the evaporative gas being fed through the evaporative gas return line L3, The cooler 25 is provided in the evaporation gas return line L3 since heat exchange is performed between the gas components being transferred through the gas recirculation line L5.

On the other hand, when the amount of evaporative gas generated in the storage tank 11 is higher than the amount of fuel required in the high-pressure natural gas injection engine and excess evaporative gas is expected to be generated, the compressed or stepwise compressed The vaporized gas is branched through the vaporized gas branch lines L7 and L8 and used in the evaporation gas consumption means. As a means of consuming the evaporative gas, a GCU, a DF Generator (DFDG), a gas turbine, etc., which can use a relatively low pressure natural gas as a fuel compared with the MEGI engine, can be used.

As described above, according to the evaporative gas treatment system and the treatment method according to the first embodiment of the present invention, the evaporation gas generated when the cargo (i.e., LNG) of the LNG carrier is transported is used as the fuel of the engine or re- It is possible to reduce or eliminate the amount of evaporated gas consumed in the GCU or the like because the refrigerant can be returned to the storage tank and stored, And the like.

Further, according to the evaporative gas processing system and the processing method according to the first embodiment of the present invention, there is no need to provide a re-liquefying device (that is, a nitrogen refrigerant refrigeration cycle or a mixed refrigerant refrigeration cycle) using another refrigerant, It is not necessary to additionally provide a facility for supplying and storing the refrigerant, so that the initial installation cost and operating cost for constituting the entire system can be reduced.

3 is a schematic configuration diagram of a boil-off gas treatment system according to a second preferred embodiment of the present invention.

The evaporative gas treatment system according to the second embodiment is configured such that when the amount of the evaporation gas required by the MEGI engine or the DF generator is greater than the amount of the evaporation gas naturally generated, the LNG can be forcibly vaporized and used Which is different from the evaporative gas processing system of the first embodiment. Hereinafter, differences from the evaporative gas processing system of the first embodiment will be described in more detail.

According to the second embodiment of the present invention, the evaporation gas (NBOG) generated and discharged from the storage tank (11) storing the liquefied gas flows along the evaporation gas supply line (L1) And is supplied to the high-pressure natural gas injection engine, for example, the MEGI engine, or supplied to the DF engine (DF Generator) during the multi-stage compression in the compressor 13, This is similar to the first embodiment.

However, in the evaporative gas processing system of the second embodiment, when the amount of evaporative gas as fuel required by the high-pressure natural gas injection engine and the DF engine is larger than the amount of evaporative gas naturally occurring in the storage tank 11, The forced vaporization line L11 is provided so that the LNG stored in the evaporator 11 can be vaporized in the forced vaporizer 31 and supplied to the compressor 13. [

When the forced vaporization line L11 is provided as in the second embodiment, the amount of LNG stored in the storage tank is small so that the amount of generated evaporation gas is small or the amount of evaporated gas as fuel required by various engines is naturally Even if the amount of generated boil-off gas is greater than that, the fuel can be stably supplied.

4 is a schematic configuration diagram showing a state in which the boil-off gas treatment system according to the present invention is used together with a fuel gas supply system for supplying fuel to an engine.

4 shows a state in which the evaporative gas processing system according to the first embodiment of the present invention shown in Fig. 2 is combined with the fuel gas supply system. However, in the evaporative gas processing system according to the second embodiment, System can be used in combination with the system.

The marine fuel gas supply system of the present invention shown in FIG. 4 includes a high pressure natural gas injection engine, for example, a MEGI engine, as a main engine, and a DF engine (DFDG) as a sub engine. Generally, the main engine is used for propulsion for the ship's operation, and the sub-engine is used for power generation to supply power to various devices and facilities installed inside the ship. However, But is not limited thereto. A plurality of main engines and sub engines may be installed, respectively.

The marine fuel gas supply system according to the present invention is a natural gas (ie, gaseous BOG and liquid) contained in the storage tank 11 for engines (ie, the main engine MEGI engine and the secondary engine DF engine). LNG can be supplied as a fuel.

In order to supply the gaseous BOG as fuel gas, the fuel gas supply system of the present invention includes a main BOG supply line L1 as an evaporation gas supply line for supplying the main engine with a BOG housed in the storage tank 11, And a BOG sub supply line L8 branching from the BOG main supply line L1 to supply the BOG to the sub engine. The BOG main supply line L1 has the same configuration as the boil-off gas supply line L1 in FIGS. 2 and 3, but in the description made with reference to FIG. 4, the BOG main supply line (ie, the BOG sub-supply for the DF engine) In order to distinguish it from the line L8), it is called BOG main supply line L1.

In order to supply the LNG in the liquid state as the fuel gas, the fuel gas supply system of the present invention includes an LNG main supply line L23 for supplying the LNG stored in the storage tank 11 to the main engine, And an LNG portion supply line L24 branching from the supply line L23 and supplying the LNG to the sub engine.

According to the present invention, the BOG main supply line L1 is provided with a compressor 13 for compressing the BOG, and the LNG main supply line L23 is provided with a high-pressure pump 43 for compressing the LNG.

The evaporated gas NBOG generated in the storage tank 11 storing the liquefied gas and discharged through the BOG discharge valve 41 is conveyed along the BOG main supply line L1 and is compressed in the compressor 13, Natural gas injection engine, such as a MEGI engine. The evaporation gas is compressed by the compressor (13) to a high pressure of about 150 to 400 bara and then supplied to the high pressure natural gas injection engine.

The storage tank has a sealing and thermal barrier to store liquefied gases such as LNG in cryogenic conditions, but it can not completely block the heat transmitted from the outside. Accordingly, evaporation of the liquefied gas is continuously performed in the storage tank 11, and the evaporation gas in the storage tank 11 is discharged to maintain the pressure of the evaporated gas at a proper level.

The compressor 13 may include one or more compression cylinders 14 and one or more intercoolers 15 for cooling the evaporated gas as it is being compressed. The compressor 13 may be configured, for example, to compress the evaporation gas to about 400 bara. 2 to 4 illustrate a multi-stage compression compressor 13 comprising five compression cylinders 14 and five intermediate coolers 15, the number of compression cylinders and intermediate coolers can be changed as needed. have. Further, in addition to the structure in which a plurality of compression cylinders are arranged in one compressor, the structure may be changed to have a structure in which a plurality of compressors are connected in series.

The evaporated gas compressed in the compressor 13 is supplied to the high-pressure natural gas injection engine through the BOG main supply line L1. In accordance with the amount of fuel required in the high-pressure natural gas injection engine, Gas injection engine, or may supply only a part of the compressed evaporated gas to the high-pressure natural gas injection engine.

The sub BOG supply line L8 for supplying the fuel gas to the DF engine which is the sub engine is branched from the main BOG supply line L1. More specifically, the sub-BOG feed line L8 branches from the main BOG feed line L1 so that the vaporized gas in the middle of the multi-stage compression process can be branched in the compressor 13. In FIGS. 2 to 4, the two-stage compressed BOG is branched and a part thereof is supplied to the sub-engine via the sub-BOG supply line L8. However, this is only an example, and the first- or third- The system may be configured so that the BOG can be branched and supplied to the sub engine via the sub BOG supply line L2. As the compressor, for example, a compressor of Burckhardt can be used. The compressor of Bochard Inc. Comprises a total of five cylinders, the three cylinders in the front are operated in an oil-free manner and the two cylinders in the rear are operated in an oil-lubricated manner. Therefore, when the compressor of the subsidiary company is used as the compressor 13 for compressing the BOG, it is necessary to configure the BOG to be transferred through the oil filter when branching the BOG in four or more stages. However, It may be advantageous in that there is no need to use a filter.

In the case of branching the BOG in the compressed state from the rear end of the compressor 13 to the high pressure because the required pressure is lower than that of the MEGI engine, the DF engine (for example, DFDG) It may be inefficient.

As described above, when the LNG is heated, since the methane component having a relatively low liquefaction temperature is preferentially vaporized, in the case of the evaporated gas, the methane content is high and can be supplied as fuel to the DF engine as it is. Therefore, there is no need to separately provide a device for methane control in the BOG main supply line and the BOG part supply line.

On the other hand, when the amount of boil-off gas generated in the storage tank 11 is larger than the amount of fuel required by the main engine and the sub-engine, it is expected that excess boil-off gas is generated. Reliquefaction can be returned to the storage tank.

When the evaporation gas exceeding the re-liquefying capacity is generated, the evaporation gas compressed in the compressor 13 or compressed in the stepwise manner is branched through the evaporation gas branch line L7 to be used in the BOG consumption means have. As the evaporation gas consumption means, a GCU, a gas turbine, etc., which can use natural gas relatively low in pressure as compared with the MEGI engine, can be used. The boil-off gas branch line L7 is preferably branched from the BOG sub-supply line L8, as shown in FIG.

At least a portion of the boil-off gas, which is compressed by the compressor 13 and then supplied to the high-pressure natural gas injection engine through the boil-off gas supply line L1, is treated through the boil-off gas return line L3, that is, liquefied, and stored in the storage tank 11. The process of returning to) is the same as described above with reference to FIGS. 2 and 3, and thus a detailed description thereof will be omitted.

2 to 4 illustrate that the boil-off gas return line L3 for supplying the compressed BOG to the heat exchanger 21 is branched at the rear end of the compressor 13, but the boil-off gas return line L3 is described above. Like one BOG supply line L2, the compressor 13 may be installed to branch off the boil-off gas in the middle of being compressed in stages. FIG. 5 shows a modified example of the two-stage compressed evaporative gas being branched by two cylinders, and FIG. 6 shows a modified example in which the three-stage compressed evaporative gas is branched by three cylinders. Particularly, in the case of using a sub-carton compressor which includes five cylinders, three cylinders in front operate in an oil-free manner and two cylinders in the rear end operate in an oil-lubricated manner, It is necessary to configure the BOG to be transferred through the oil filter when branching the BOG at the rear stage or the fourth stage or more, but it may be advantageous in that it is not necessary to use the oil filter when branching at the third stage or less.

The LNG main supply line L23 is provided with a discharge pump 12 installed inside the storage tank 11 for discharging the LNG to the outside of the storage tank 11, Pressure pump 43 for secondarily compressing the supplied LNG to a pressure required by the MEGI engine. The discharge pumps 12 may be installed one by one in each storage tank 11. Although only one high-pressure pump 43 is shown in FIG. 4, a plurality of high-pressure pumps may be connected in parallel, if necessary.

As described above, the pressure of the fuel gas required by the MEGI engine is as high as 150 to 400 bara (absolute pressure). In the present specification, "high pressure" should be regarded as meaning a pressure of about 150 to 400 bara (absolute pressure) required by the MEGI engine.

The LNG discharged from the storage tank 11 storing the liquefied gas through the discharge pump 12 is conveyed along the LNG main supply line L23 and supplied to the high pressure pump 43. [ Subsequently, the LNG is compressed to a high pressure by the high-pressure pump 43 and then supplied to the vaporizer 44 to be vaporized. The vaporized LNG is supplied as fuel to a high pressure natural gas injection engine, such as a MEGI engine. Since the pressure required by the MEGI engine is supercritical, LNG compressed at high pressure is neither gas nor liquid. Therefore, the expression of vaporizing the LNG compressed at the high pressure in the vaporizer 44 should be regarded as meaning that the temperature of the supercritical LNG is raised to the temperature required by the MEGI engine.

The sub LNG supply line L24 for supplying the fuel gas to the DF engine which is the sub engine is branched from the main LNG supply line L23. More specifically, the secondary LNG supply line L24 is branched from the main LNG supply line L23 so that the LNG before the high-pressure pump 43 can be branched.

A vaporizer 45, a gas-liquid separator 46, and a heater 47 are provided in the secondary LNG supply line L24 to adjust the methane temperature and the temperature of the LNG supplied as fuel to a value required by the DF engine.

As described above, in the case of LNG, the methane content is relatively low, which is lower than the methane price required by the DF engine, and the ratio of the hydrocarbon components (methane, ethane, propane, butane, etc.) It is not suitable for vaporizing it as it is and supplying it to the DF engine as fuel.

To regulate the methane gas, the LNG is heated in the vaporizer 45 and partially vaporized. The fuel gas, which is partially vaporized and mixed with the gaseous state (i.e., natural gas) and the liquid state (i.e., LNG), is supplied to the gas-liquid separator 46 to be separated into gas and liquid. Since the vaporization temperature of the high-calorific heavy hydrocarbon (HHC) component is relatively high, the proportion of the heavy hydrocarbon component in the remaining liquid LNG that is not vaporized in the partially vaporized fuel gas becomes relatively high. Therefore, by separating the liquid component from the gas-liquid separator 46, that is, separating the heavy hydrocarbon component, the methane gas of the fuel gas can be increased.

The heating temperature in the vaporizer 45 can be adjusted in order to obtain an appropriate methane gas in consideration of the ratio of the hydrocarbon component contained in the LNG and the methane demanded by the engine. The heating temperature in the vaporizer 45 can be set within a range of approximately -80 to -120 degrees centigrade. The liquid component separated from the fuel gas in the gas-liquid separator 46 is returned to the storage tank 11 through the liquid component return line L5. The evaporation gas return line L3 of the evaporation gas treatment system and the liquid component return line L25 of the fuel gas supply system may be joined and then extended to the storage tank 11. [

The methane-regulated fuel gas is supplied to the heater 47 through the LNG portion feed line L24, further heated to a temperature required by the sub-engine, and then supplied to the sub-engine as fuel. If the sub-engine is, for example, DFDG, the methane required is generally greater than 80. For example, in the case of General LNG (typically methane: 89.6%, nitrogen: 0.6%), the methane level before the separation of the heavy hydrocarbon component is 71.3 and the lower heating value at that time is 48,872.8 kJ / kg atm, saturated vapor standard). When this General LNG is pressurized to 7 bara and heated to -120 ° C to remove the heavy hydrocarbon component, the methane gas is increased to 95.5, and the LHV at that time is 49,265.6 kJ / kg.

According to the present invention, there are two paths for supplying the fuel gas to the engines (main engine and sub engine). That is, the fuel gas may be supplied to the engine after being compressed through the compressor 13, compressed through the high-pressure pump 43, and then supplied to the engine.

In particular, ships such as LNG carriers and LNG RVs are used to transport LNG from the production site to the consumer site. Therefore, when operating from the production site to the consumer site, it is necessary to operate Laden as a storage tank full of LNG, When returning to production site, the storage tank is operated in a ballast state with almost empty space. Since the amount of LNG is large in the laid-in state, the amount of evaporation gas is relatively large, and in the ballast state, the amount of LNG is small and the amount of evaporation gas is relatively small.

Although there are some differences depending on the conditions of the storage tank capacity, external temperature, etc., for example, the amount of boil-off gas generated when the storage tank capacity of LNG is approximately 130,000 m 3 to 350,000 m 3 is about 3 to 4 ton in Leiden. / h and about 0.3 to 0.4 ton / h in ballast. In addition, the amount of fuel gas required in the engines is approximately 1 to 4 ton / h (approximately 1.5 ton / h) in the case of the MEGI engine and approximately 0.5 ton / h in the case of the DF engine (DFDG). On the other hand, since the BOR (Boil Off Rate) is gradually lowered as the insulation performance of the storage tank is improved recently, the amount of BOG generated is also decreasing.

Therefore, when the compressor line (i.e., L1 and L8 in FIG. 4) and the high pressure pump line (i.e., L23 and L24 in FIG. 4) are provided together with the fuel gas supply system of the present invention, a large amount of evaporated gas is generated. It is preferable to supply fuel gas to the engines through the compressor line in the laden state, and to supply the fuel gas to the engines through the high pressure pump line in a ballast state in which the amount of boil-off gas is generated.

Generally, the energy required to compress a gas (BOG) by a compressor to a high pressure of 150 to 400 bara (absolute pressure) required by a MEGI engine is much higher than the energy required to compress the liquid (LNG) It is conceivable that using only a high pressure pump line without a compressor line is economical, because energy is required and the compressor for compressing the gas at high pressure is quite expensive and takes up a large volume. For example, 2MW of power is consumed to fuel a ME-GI engine by driving a set of multi-stage compressors. Only 100kW of power is consumed by using a high-pressure pump. However, when the fuel gas is supplied to the engines using only the high-pressure pump line in the laid-open state, a liquefaction device for re-liquefying the BOG in order to treat BOG continuously occurring in the storage tank is indispensable, , It is advantageous to install the compressor line and the high-pressure pump line together to supply the fuel gas through the compressor line in the layon state and the fuel gas through the high-pressure pump line in the ballast state.

On the other hand, when the amount of boil-off gas generated in the storage tank does not reach the amount of fuel required by the ME-GI engine, such as in a ballast state, the multi-stage compressor does not compress the boil-off gas to the high pressure required by the ME-GI engine and It may be efficient to divert the boil-off gas through the BOG branch line L7 during compression and use it as fuel in the DF engine. That is, for example, if evaporative gas is supplied to the DF engine through only the second-stage compression cylinder of the five-stage compressor, the remaining three-stage compression cylinders are idle. When the evaporator is driven by compressing the entire 5-stage compressor, the required power is 2MW. If only the second stage is used and the remaining three stages are idle, the required power is 600kW. The required power is 100 kW. Therefore, when the BOG generation amount is less than the fuel amount required in the ME-GI engine, such as the ballast condition, it is advantageous from the energy efficiency standpoint that the BOG consumes the entire amount in the DF engine and supplies the LNG as fuel through the high pressure pump.

However, even if the BOG generation amount is less than the fuel requirement amount in the ME-GI engine, the BOG may be supplied as fuel to the ME-GI engine through the compressor while supplying the LNG by the deficient amount. Instead of discharging the BOG every time the BOG is generated, the BOG is collected without releasing the BOG until the storage tank reaches a certain pressure, and then discharged intermittently to the DF engine or ME-GI And may be supplied as fuel to the engine.

In addition, in ships where equipment repair and replacement is not easy, it is necessary to install two important facilities in case of an emergency (redundancy; that is, dual design). In other words, the ship is provided with an extra facility that can perform the same function as the main facility, so that when the main facility is in normal operation, It is required to design redundantly important facilities. Examples of facilities requiring dual design include rotary-driven equipment such as compressors and pumps.

In this way, the ship needs to be equipped with a plurality of facilities in order to satisfy only the dual requirement without being usually used. The fuel gas supply system using two compressor lines requires a great deal of cost There is a problem that a space is consumed and a lot of energy is consumed in use, and a fuel gas supply system using two high-pressure pump lines may have a problem that a large amount of energy is consumed in processing (i.e., re-liquefying) evaporative gas. In contrast, the fuel gas supply system of the present invention, in which a compressor line and a high-pressure pump line are installed together, can continue normal operation through the other supply line even if a problem occurs in one of the supply lines. If only one compressor line is installed It is possible to reduce the cost of the first drying operation as well as the operation cost by appropriately selecting and operating the optimum fuel gas supplying method according to the amount of generated evaporation gas while using less expensive compressor.

As shown in FIG. 4, when the evaporative gas treatment system and the fuel gas supply system are combined according to the present invention, the evaporative gas generated when the cargo (i.e., LNG) of the LNG carrier is transported is used as the fuel of the engine, It is possible to reduce or eliminate the amount of evaporated gas that is consumed in the GCU or the like, and it is unnecessary to provide a re-liquefying device using a separate refrigerant such as nitrogen, Can be re-liquefied and processed.

According to the present invention, despite the recent trend that the capacity of the storage tank is increased and the amount of evaporation gas is increased and the performance of the engine is improved and the amount of fuel required is decreased, the evaporation gas remaining as fuel of the engine is re- It is possible to return to the storage tank, thereby preventing waste of the evaporated gas.

Particularly, according to the evaporation gas processing system and the processing method of the present invention, it is not necessary to provide a re-liquefying apparatus using a separate refrigerant (i.e., a nitrogen refrigerant refrigeration cycle or a mixed refrigerant refrigeration cycle) It is possible to reduce the initial installation cost and the operating cost for constructing the entire system.

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

11: Storage tank 12: Discharge pump
13: compressor 14: compression cylinder
15: Intermediate cooler 21: Heat exchanger
22, 24: expansion valve 23: gas-liquid separator
25: cooler 31: forced vaporizer
41: BOG discharge valve 43: high pressure pump
44, 45: vaporizer 46: gas-liquid separator
47: Heater
L1: Evaporation gas supply line, BOG main supply line as evaporation gas supply line
L3: Evaporative gas return line L5: Evaporative gas recirculation line
L7: Evaporative gas branch line L8: BOG part supply line
L11: Forced vaporization line L23: LNG main supply line
L24: LNG part supply line L25: liquid component return line

Claims (11)

A method of treating a boil-off gas on a ship having a storage tank storing liquefied natural gas and a high-pressure natural gas injection engine using the boil-off gas discharged from the storage tank as a fuel,
A compression step of receiving the boil-off gas generated in the storage tank and compressing the compressed gas with a compressor;
Supplying a portion of the boil-off gas compressed in the compression step to supply a portion of the boil-off gas as fuel to the high-pressure natural gas injection engine;
A liquefaction step of liquefying the remaining evaporated gas which is not supplied as fuel to the high pressure natural gas injection engine by exchanging the evaporated gas with a heat exchanger before being compressed after being discharged from the storage tank;
A decompression step of lowering the pressure of the boil-off gas liquefied in the heat exchanger;
Including;
In the liquefaction step, a part of the compressed boil-off gas not supplied to the high-pressure natural gas injection engine is liquefied by exchanging heat with the boil-off gas discharged from the storage tank and transferred to the compressor,
The gas component of the evaporation gas of the vessel decompressed in the depressurization step, the gas component is discharged from the storage tank is joined to the boil-off gas supplied to the compressor characterized in that the vessel. delete The method according to claim 1,
After the liquefaction step, and further comprising the step of returning to the storage tank after the pressure of the boil-off gas liquefied in the heat exchanger further comprising the step of returning to the storage tank. The method according to claim 3,
A method of treating a boil-off gas on a ship, characterized in that to remove only liquid components from the boil-off gas under reduced pressure and returning to the storage tank. The method according to claim 1,
And further cooling the boil-off gas liquefied in the heat-exchanger by heat-exchanging with the gaseous components of the boil-off gas which has been decompressed and gas-liquid mixed. delete The method according to claim 1,
The compressor is a method of treating a boil-off gas on a ship, characterized in that it comprises a plurality of compression cylinders. The method of claim 7,
And a boil-off gas consuming means for receiving and using a boil-off gas compressed through a portion of the plurality of compression cylinders included in the compressor. The method of claim 7,
The boil-off gas sent to the heat exchanger is a boil-off gas treatment method, characterized in that the boil-off gas compressed through some or all of the plurality of compression cylinders included in the compressor. The method according to claim 1,
And a forced vaporization step for forcibly vaporizing the liquefied natural gas stored in the storage tank and supplying the compressed gas to the compressor. The method according to claim 1,
The ship,
A compressor line for compressing the evaporated gas generated in the storage tank by the compressor and supplying the compressed natural gas as fuel to the high pressure natural gas injection engine;
A high pressure pump line for compressing LNG contained in the storage tank by a high pressure pump to supply the high pressure natural gas injection engine as fuel;
Evaporation gas treatment method of a ship comprising a.

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