KR101904367B1 - Utilization of lng used for fuel to liquefy lpg boil off - Google Patents

Abstract

The present invention relates to a method and system for liquefying LPG vapor (BOG), said system comprising an LNG fuel supply system comprising at least one LNG fuel tank (23), an LNG fuel line 5 and the second LNG fuel line 13; And an LPG cargo system comprising at least one LPG cargo tank (20), an evaporative gas (BOG) line (1), at least one resupply unit (100) and a condensate line (3); The system further comprises at least one evaporator (15, 22) provided on the LNG fuel line (5) between the LNG fuel tank (23) and the second LNG fuel line (13) (15, 22) are heat exchanged with the LPG cargo system.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to an LNG used as a fuel for liquefying LPG vapor,

The present invention relates to a system and a method for utilizing LNG used as fuel to liquefy LPG vaporized gas.

Currently, ships carrying LPG (Liquefied Petroleum Gas) use mainly low-speed diesel engines for their main propulsion, and engine fuels use various types of marine fuels. However, new environmental regulations, already known as emission control areas, limit the release of sulfur, nitrogen oxides and particulate matter into the atmosphere. In the future, strict international emission controls are also expected. Several measures have been proposed by the industry to purify exhaust gases, for example, to meet new requirements. Another option is to use clean, lean burn fuel such as methane. For the marine industry's diverse fuel consumption and wide sailing range requirements, methane should be stored in the most efficient manner in a liquid state known as Liquefied Natural Gas (LNG).

LNG fuel systems are generally known in the prior art, one example of which is disclosed in Norwegian Patent Application No. 20093272, entitled " LNG Fuel Tank System for At least One Gas Engine for Propelling a Ship " .

LPG carriers usually have four cargo tanks that share a common steam atmosphere when transporting one type of cargo. The LPG carrier is designed to be capable of transporting two different cargoes at the same time. This means that two piping systems are installed on the deck to enable complete separation of the two cargo systems. The LPG carrier may, for example, be loaded with propane in three tanks and butane in a fourth cargo tank. The three tanks loaded with propane have a vapor communication space, but are thoroughly isolated from the butane vapor space. Each deck piping system is connected to a plurality of refueling units which ensure that the cargo tank pressure does not exceed the maximum permissible pressure. The re-liquefying unit compresses the evaporation gas with sufficient pressure so that the gas can be condensed against the seawater. The condensate is returned to the cargo tank. In this way the cargo tank pressure is kept low. Very Large Gas Carrier (VLGC), which is fully loaded and navigated at maximum ambient temperature conditions, typically has a fuel oil consumption (to the generator) of approximately 1,900 kg / day for liquefying the evaporation gas at a cargo carrying capacity of approximately 82.000 m ³ . In addition, due to the fact that LNG has a density of less than about 50% less than marine diesel oil, LNG has twice the storage volume Another problem associated with the transport of LPG in the North Sea basin, for example, is that the duration of the voyage is short, The result is that the harbor time is significantly related to the total round trip duration and therefore the reduction in berth time is important.

Because all rotating devices have maintenance intervals based on run time, maintenance and maintenance of the refrigeration compressor is another operational cost issue. Newly constructed vessels usually have docking intervals of five years, while freezing compressors are maintained at approximately 20,000 hour intervals. Therefore, it is judged that maintenance is required during the voyage. Thus, it would be advantageous to reduce the total running time, thereby extending the time of the maintenance intervals, and preferably allowing the maintenance intervals to be adjusted to docking intervals.

It is therefore an object of the present invention to provide a system and method for utilizing an LNG used as a fuel to liquefy LPG evaporation gas, thereby solving at least one of the above problems.

To solve this problem, the present invention discloses a system for liquefying LPG evaporation gas (BOG), comprising at least one LNG fuel tank (23), an LNG fuel line (5) and a second LNG fuel line (LNG) fuel supply system (10); Comprising an LPG cargo system comprising at least one LPG cargo tank (20), an evaporation gas line (1), at least one refueling unit (100) and a condensate line (3) Further comprising at least one evaporator (15,22) provided in the LNG fuel line (5) between the fuel tank (23) and the second LNG fuel line (13), the at least one evaporator Exchanges heat with the LPG cargo system.

The present invention also relates to an LNG fuel supply system comprising at least one LNG fuel tank 23, a first LNG fuel line 5 and a second LNG fuel line 13; A system comprising an LPG cargo system comprising at least one LPG cargo tank (20), an evaporation gas line (1), at least one refueling unit (100) and a condensate line (3) The method also includes providing at least one evaporator (22, 15) positioned on a first LNG fuel line (5) between the LNG fuel tank and the second LNG fuel line (13); Condensing the evaporated gas (BOG) by evaporation of the LNG flowing out from the LNG fuel tank; And sending the condensed evaporative gas (BOG) to an LPG cargo tank. Typically, the number of evaporators 22, 15 coincides with the number of simultaneously transportable cargoes. This is usually two.

Other preferred embodiments of the present invention may be understood by reference to the dependent claims of the claims and the following detailed description with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of a prior art liquefaction unit.
Figure 2 is a schematic diagram of one embodiment of a system according to the present invention.
3 is a schematic diagram of another embodiment of a system according to the present invention.

LPG should be understood as oil gas of various grades or product ranges that are stored and transported as liquefied goods. Among the various petroleum gases, propane and butane are major examples, propane typically containing ethane at any concentration between 0% and 5% by volume, and butane content in propane ranging from 0% to 20% by volume And has arbitrary concentration. Such a mixture, which is typically composed of 70% by volume to 98% by volume of propane, is known as propane, which is hereinafter referred to as propane.

Butane can be any mixture of normal-butane and iso-butane with a proportion of unsaturated hydrocarbons, hereinafter referred to as butane.

Furthermore, propane and butane LPG should contain at least the following components:

Ammonia,

Butadiene,

Butane-Butane mixture (all mixtures),

Butylenes,

Diethyl ether,

Propylene,

Vinyl chloride.

LPG stored and transported at temperatures below room temperature will continue to release a certain amount of steam naturally. A common process of maintaining pressure in cargo tanks is to extract, liquefy, and return these vapors to the cargo tank in a condensed state. The re-liquefaction unit is hereinafter referred to as a refrigeration unit for liquefying the vapor and the prefix " re "refers to liquefaction of the vapor from the liquefied gas.

The LPG is transported in a liquid state at a higher pressure than the atmospheric pressure, a temperature lower than the ambient temperature, or a combination of the two. The present invention relates to an LPG carrier, known as a so-called fully cooled LPG carrier, which transports liquefied cargo, i.e., LPG, at a temperature lower than ambient temperature; Lt; RTI ID = 0.0 > LPG < / RTI > carrier transporting liquefied cargo and LPG at pressures above ambient and below ambient. The latter LPG carrier is known as semi-refrigerated / semi-pressurized.

Cargo types are any of the above-mentioned grades or LPG of the product.

The condensate should be understood as liquefied vapor, where the vapor is the vapor exiting the cargo due to constant heat leakage to the cargo tank.

Hot cargo is LPG loaded at temperatures above the LPG saturation temperature at the current cargo tank pressure.

BACKGROUND ART [0002]

Korean Patent Publication No. 20100102872 discloses a method for use in a composite ship capable of simultaneously loading LPG and LNG, or a floating production storage and unloading vessel. The invention described in Korean Patent Publication No. 20100102872 discloses the utilization of the low temperature of the LNG evaporation gas prior to compression and liquefaction to condense the LPG evaporation gas to reduce the complexity of the LPG re-liquefaction system.

Korean Patent Publication No. KR 20100102872 discloses a method for condensing LPG vapor with a latent heat and a sensible heat of LNG in combination with an LNG fuel gas system in order to condense the LPG evaporation gas, Lt; / RTI >

U.S. Patent No. 5,860,294 discloses a method of condensing gaseous hydrocarbons from a mixture of inert and gaseous hydrocarbons, and more particularly to a storage tank for LPG / LEG (LEG = Liquefied Ethylene Gas) vessels.

U.S. Patent No. 5,860,294 describes a remanufacturing system similar to the remanufacturing unit 100 of the present invention, but it is also possible to use a downstream second condensing system (not shown) for recovering gaseous hydrocarbons from a gaseous mixture that will not condense in a normal cargo condenser .

In order for the second condensing system of US Pat. No. 5,860,294 to function, the main cargo condenser must be in operation and partial condensation must occur at the exchanger.

The second condensation system 22 in the present invention is located upstream of the cargo material liquefaction system and does not depend on the operation of the main cargo condenser.

Korean Patent Laid-Open Publication No. 20010077227 discloses a method for re-liquefaction of an LNG evaporation gas, for example, to a portion of an LNG stream sent to an evaporator before being sent to a national natural gas distribution grid, Is liquefied. Evaporative gas condensate is mixed with the LNG export line. Condensate does not return to the storage tank.

Liquid LNG is used to control the pressure in the LNG storage tank by heat exchange / absorption of the evaporated gas into the LNG prior to evaporation of the combined LNG and condensate streams.

European Patent Publication EP 1990272 is in principle similar to Korean Patent Publication No. 20010077227, but the condensate returns to the storage tank and the evaporated material is sent as fuel to the gas engine.

US Patent No. 3306660 discloses a method and system for storing multi-component cryogenic fluids wherein more volatile components that are naturally evaporated are obtained, condensed, and reintroduced into the storage tank. The cryogenic liquid that is pumped out is used to condense evaporative gases.

International Patent Publication No. WO 2011062505 discloses a process for recovering evaporative gas from an LNG storage tank, wherein the LNG is sent to a re-condensing tank that absorbs the LNG vapor.

U.S. Pat. No. 2,795,937 discloses a process and apparatus for the storage and transport of liquefied gases, wherein the first tank has liquefied natural gas (LNG) and the first tank has a higher boiling point liquid. Prior to entering the combustion engine by heat exchange in the tank liquid of the higher boiling temperature liquid, the LNG is used as fuel in the vessel, evaporated and heated. U.S. Pat. No. 2,795,937 teaches that such heat exchange prevents evaporation from the liquid surface and does not require an evaporative gas remelting system.

U.S. Patent No. 3,864,918 discloses a method in which evaporative gas is obtained from an LNG tank and separated into two components of the stream. The first stream is compressed, cooled, and liquefied. The second flow is used as fuel to drive the ship.

U.S. Patent Application Publication No. 2006/0053806 describes a system for supplying evaporative gas as fuel as a marine LNG carrier fuel and for pressure control of a cargo tank.

1 shows, by way of reference, a typical prior art liquefaction unit 100 connected to at least one cargo tank 20. Cargo loading lines are not shown. The evaporated gas from the cargo tank 20 flows through the evaporative gas line 1 to the cargo compressor 40, which is typically a first stage multi-stage compressor, and the steam is compressed to an intermediate pressure. Any amount of vapor that has not been treated by the refill liquor unit shown in Figure 1 flows through the evaporation gas line 51, which is installed in parallel with the operating unit, not shown.

The evaporated gas exiting the cargo compressor 40 through line 46 enters the economizer 43 where the evaporated gas is near the saturation temperature. The evaporation gas then flows from the economizer 43 through the line 47 to the cargo compressor 41 where the evaporation gas reaches a bubble point pressure corresponding to the temperature obtainable by the cargo condenser 42 . The cargo compressor 41 is typically a second stage multi-stage compressor. Sometimes two or more compression stages are required, and these may typically be installed in series with the cargo compressor 41.

The compressed vaporized gas then enters the cargo condenser 42 via line 48 and is condensed by the seawater or any cooling medium, typically above sea water temperature. Seawater is by far the most commonly used heat sink for cargo condenser 42, but it is also possible to mix water with an anti freeze agent. The antifreeze can be any suitable glycol.

The warm condensate leaving the cargo condenser 42, which is the product of the evaporated gas condensed from the cargo condenser 42, flows to the economizer 43 via line 49. Line 50 branches at line 49 where a small portion flows through a level control valve 44 that provides the necessary intermediate cooling and subcooling for the main portion of the warm condensate. In general, a liquid receiver is mounted on the line 49 although not shown. Residual warm condensate returned to the cargo tank 20 is diverted through the coil 52 in the economizer 43 and further flows from the coil 50 into the subcooled state ) Through the coil (52). The present auxiliary cooled condensate flows through line 3 and is returned to the cargo tank. A condensate production valve (45) regulates the amount of condensate flow returned to the cargo tank (20). Condensate from another remelting unit arranged in parallel, not shown, is connected to line 3.

Figure 2 shows an LNG over-stippled line and LPG cargo system, two separate compartmented systems to date. The LNG fuel gas supply system is provided with one or more connected LNG fuel tanks (23). In order to ensure that the vapor pressure in the fuel tank 23 is higher or lower than a certain vapor pressure and in order to ensure a more sufficient fuel gas supply pressure in the fuel line 5, the fuel gas supply system is provided with an LNG And a valve 27 for controlling the amount of fluid. According to the well-known principle, LNG is fed to the evaporator 25, the LNG is evaporated and the resulting steam flows into the superheater 26 and before being conveyed to the main engine via line 3, Lt; / RTI > A steam line 8 and a valve 28 are also shown in Fig. 2 that allow the evaporated gas of the LNG to be sent to the superheater 26 when a reduction in pressure in the fuel tank 23 is required. However, there is no flow in the steam line 8 in many situations.

Engine Fuel Gas injection pressure varies depending on whether the engine is an auto or diesel engine, while a gas injection pressure of 300 to 350 bar is required for a diesel engine, while an auto engine requires only a proper gas injection pressure of 4 bar. Apart from requiring replaceable high pressure dedicated pumps for pressure rise, this significant difference in pressure has a limited effect on the present invention. Additional pump systems are not shown because they are generally known to those of ordinary skill in the art.

As described above, in a diesel engine requiring high fuel gas pressure, an additional LNG fuel pump is required which is connected to the fuel line 5 to raise the LNG pressure to the required pressure until entering the evaporator 25. [ In this embodiment, the steam line 8 leads to a safe location or, alternatively, to a utility consumer, where there is no flow in the steam line 8 in most situations.

As described above with reference to Figure 1, the LPG cargo system of Figure 2 includes a re-liquefaction unit 100 and at least one LPG cargo tank 20, a boil of gas flowing into the liquefaction unit 100 There is provided a condensate line 3 for returning the evaporation gas line BOG line 1 and the condensate to the cargo tank 20 through the valve 45.

Considering general voyage, a typical Very Large Gas Carrier (VLGC) at maximum ambient temperature conditions carrying propane has heat leakage to a cargo tank system of approximately 425 kW. The LPG evaporation rate generated is on average about 3,300 to 3,800 kg / hr. In addition, the propulsive force typically installed in a super large gas carrier (VLGC) is 14 MW, which typically consumes 7500 kJ / kWh at maximum continuous rated output, where the required amount of LNG is about 2,120 kg / h . Thus, the refrigeration potential of LNG in all practical conditions will cause the liquefaction unit to operate during laden voyage, especially at ambient temperature below maximum design and / or at maximum continuous rated output You will not need to. In fact, re-liquefaction behavior can be eliminated completely under these conditions.

Therefore, a system according to the present invention that utilizes LNG used as fuel to liquefy evaporated LPG is provided at least between the LNG fuel line 23 and the second LNG fuel line 13, Wherein the at least one evaporator (15, 22) is in heat exchange with the LPG cargo system to effectively integrate the LNG fuel system into the LPG evaporative gas system.

The dedicated blower installed on the evaporative gas line, which is fed directly to the evaporator 22, is obviously optional, but when there is an already installed cargo compressor, the cost of the additional equipment is increased. Moreover, such a solution is undesirable and therefore not shown. However, as an alternative, it is also possible to allow the vapor to flow freely to the evaporator 22, and a return pump must be considered for this combination.

According to a first embodiment of the invention, at least one evaporator 22 is arranged to evaporate the LNG flowing through the line 5 by pressure in the fuel tank 23, thereby evaporating the evaporated gas (BOG) Gas condenser (BOG condenser). The condensate is sent back to cargo tank 20 via line (2). Looking at other routes around, LNG evaporates depending on the amount of evaporative gas and the amount of fuel consumed for the evaporative gas, where the LNG is partially evaporated, completely evaporated, or completely evaporated and overheated. The product leaves the evaporator 22 and enters the evaporator 25 where the remaining LNG is evaporated. The steam flows from the evaporator 25 to the superheater 26 where the steam is heated to the desired fuel gas temperature. Both the evaporator 25 and the superheater may be omitted in the case of the amount of fuel consumption and evaporation amount of the LNG in which the steam leaving the at least one evaporator 22 is overheated. In the case of the fuel consumption and the evaporation amount of the LNG from which the vapor leaving at least one evaporator 22 is completely evaporated, the evaporator 25 may be omitted.

In the above-described embodiment, the flow of all the LNG passes from the fuel tank 23 through the evaporator 22. However, under certain circumstances, it may be advantageous, for example, to control the flow of LNG through the evaporator, such as an insufficient evaporative gas or a no boil off gas. According to an embodiment of the present invention, two valves 29, 29 are provided so that when the evaporation gas line 1 is free of evaporation gas, the valve 29 is opened and the valve 30 is closed and vice versa, 30 are provided on the front surface of the evaporator 22 and in parallel with the evaporator. The valves 29 and 30 regulate the amount of LNG flowing into the evaporators 22 and 15, the current LNG consumption and the amount of available evaporative gas (BOG) in the evaporative gas line 1. This embodiment fully evaporates the resulting material leaving the evaporators 22 and 15 and ensures that the steam is transferred to a superheater 26 where the steam is heated to the desired fuel gas temperature. Regulation is based on known principles and is not shown. Any surplus LNG that is not needed in the evaporators 22 and 15 is directly conveyed to the evaporator 25 where the surplus LNG is evaporated before being conveyed to the superheater 26. [ Valves 29 and 30 are equally well replaceable with a three-way valve, not shown. The valve 29, 30 device thus represents a replaceable valve device that provides the same function.

The piping system around the cargo compressors 40, 41 in the liquefaction unit 100 operates in a single stage compression mode. The arrangement of the cargo compressors 40, 41 in the one-stage compression mode is evident by the ordinary artisan, and the proposal is one of several possible solutions. In one stage of compression, volumetric capacity is high, usually only one compressor is required to be in operation and thus provides a total reduction in overall compression drive time. The vaporized gas from the LPG cargo tank 20 then flows directly to the cargo compressors 40 and 41 where the vaporized gas is lifted under normal pressure in line 1. At a convenient location on line 48 or line 49 the compressed gas is diverted through line 61 and the evaporated gas is condensed back to cargo tank 20 through line 2 to evaporator 22 Flows. The valve 71 and the valve 72 regulate where the branch of the evaporation gas is formed.

In another embodiment of the present invention at least one evaporator 15 is a condensate sub cooler provided on the condensate line 3 and a condensate subcooler provided between the refueling unit 100 and the cargo tank 20 The condensate subcooler 15 is adapted to subcool the LPG condensate by evaporating the LNG from the fuel tank 23. The condensate subcooler in the embodiment as described above with reference to the evaporative gas (BOG) condenser 22 can be used alone.

In the preferred embodiment of the present invention, as described in the following detailed description, both the evaporator 15 and the evaporator 22, which, when available, increase the flexibility and operational flexibility of excessive refrigerant capacity within the LNG Is provided. In this embodiment, a valve 16 and a valve 17 are provided to bypass or allow passage of the evaporator 15.

According to an exemplary embodiment of the present invention, the evaporated gas discharged from the LPG cargo tank 20 flows directly to the cargo compressors 40 and 41 where the evaporated gas pressure in the line 1 is suitably increased. The piping system around the cargo compressors (40, 41) in the remelting unit (100) is arranged to operate in one stage of compression mode. The compressed gas suitably compressed from the cargo compressors 40 and 41 flows to the evaporator 22 where the vaporized gas is condensed through the line 2 and returned to the cargo tank 20.

The evaporated gas (BOG) in the evaporator 22 is condensed by evaporating the LNG flowing through the line 5 by pressure from the fuel tank 23. The condensed evaporated gas (BOG) is sent back to cargo tank 20 through line 2. As another way around, the LNG is evaporated against the evaporative gas, and depending on the amount of current evaporation and the current consumption of fuel, the LNG is partially evaporated, completely evaporated, or completely evaporated and overheated. The product leaves the evaporator 22 and enters the evaporator 25 where the remaining LNG is evaporated. The vapor is transferred from the evaporator 25 via line 12 to a superheater 26 where the vapor is heated to the desired fuel gas temperature. Both the evaporator 25 and the superheater may be omitted in the case of the fuel consumption amount and the evaporation gas amount of the LNG in which the steam leaving the at least one evaporator 22 is overheated. In the case of the fuel consumption and the evaporation amount of the LNG from which the vapor leaving at least one evaporator 22 is completely evaporated, the evaporator 25 may be omitted.

In the embodiment described above, all of the LNG flows from the fuel tank 23 through the evaporator 22. However, under certain circumstances, it may be advantageous, for example, to control the flow of LNG through the evaporator, such as an insufficient evaporative gas or a no boil off gas. According to an embodiment of the present invention,

 Each of the two valves 29 and 30 is connected to an evaporator (not shown) so that the valve 29 is opened and the valve 30 is closed when the evaporative gas line BOG line 1 is empty, 22 and in parallel with the evaporator. The two valves 29 and 30 are also capable of adjusting the amount of LNG flowing into the evaporators 22 and 15, the current LNG consumption and the amount of available evaporation gas (BOG) in the evaporative gas line (BOG line, 1) . The LNG flowing to the evaporators 22, 15 is completely evaporated and the vapor is transferred to the superheater 26 where the vapor can be heated to the desired fuel gas temperature. Any surplus LNG that is not needed in the evaporators 22 and 15 is transferred directly to the evaporator 25 and the surplus LNG is evaporated before being sent to the superheater 26. [ The two valves 29 and 30 are equally well replaceable with a three way valve providing the same function.

In the exemplary embodiment disclosed above, the use of the system during laden voyage when the LNG fuel consumption is high has been mentioned. However, during loading, the remelting unit 100 must be in an operating state since the evaporation rate is the maximum and the LNG fuel consumption is at the low lower limit.

Under these conditions, it will naturally be considered to reduce the amount of LNG usable during optimal shipment utilized in the evaporator 22 as a precooler in the liquefaction unit.

Under these conditions it is of course contemplated that the reduced amount of LNG that is the highest available during loading is utilized in the apparatus represented by reference numeral 22, which functions as a pre-cooler leading to the liquefier unit. However, this is not an optimal solution, especially when hot cargo is shipped, for example due to fog problems at the compressor inlet.

Instead of pre-cooling the evaporated gas, subcooling the condensate reduces the generation of flash gas in the cargo tank 20 and thus does not recycle the flash gas returning to the cargo compressor Thereby increasing system efficiency.

During the loading, all the evaporated gas is sent directly through the line 1 to the refueling unit, where the evaporated gas condenses and returns via line 3. In line 3, the condensate subcooler 15 is located using LNG as the refrigerant. Before being returned to the cargo tank, the condensate is reduced, preferably at a temperature not below -50 占 폚. The condensate temperature depends on the type of cargo and can be increased for more types of warm cargo.

As mentioned earlier, the LPG carrier is made to carry two different cargoes at the same time, and the two cargoes can be propane and butane. The evaporators 22 and 15 operate in a sequential order wherein the LNG is first evaporated with respect to the propane in at least one evaporator 22 and then the evaporated LNG is introduced into the line 74 in the parallel unit operating on butane, To the line 80. [ The resulting higher evaporated LNG is returned to the fuel gas system via line (5). Figure 3 shows how this could be done with one tank of butane loaded and three tanks loaded with propane. Typically four liquefaction units 100 will be installed, but two of the usual voyages will be standby, especially when LNG is used as fuel according to the present invention. It is also possible that the evaporator 22 can be seen from the diagram parallel operation. Figure 3 does not show a standby remelting unit.

While the invention has been described and illustrated in detail in the drawings and foregoing description, such description and description are to be regarded as illustrative and not in a limiting sense, and are not intended to limit the invention to the disclosed embodiments. The mere fact that certain features are quoted in different dependent claims does not indicate that a combination of these features can not be used to advantage. No reference signs in the claims should be construed as limiting the scope of the invention.

Claims (9)

A second LNG fuel line 13 connected in series to the first LNG fuel line 5 downstream of the at least one LNG fuel tank 23, the first LNG fuel line 5 and the first LNG fuel line 5, An LNG fuel supply system having an LNG supply system; An LPG evaporation gas (BOG) comprising an LPG cargo system comprising at least one LPG cargo tank (20), at least one refueling line (100) provided with an evaporation gas line (1) and a condensate line (3) A system for liquefying a liquid,
A system for liquefying the LPG vaporized gas (BOG)
Two evaporators 15 and 22 provided on the first LNG fuel line 5 between the LNG fuel tank 23 and the second LNG fuel line 13 and two evaporators 15 and 22 provided on the first LNG fuel line 5, At least one evaporator (25) disposed downstream of the evaporator (22); And
The amount of LNG flowing through the evaporator 22 can be adjusted to match the amount of current LNG fuel consumption and the amount of available evaporative gas BOG present in the evaporative gas line 1, (29, 30) arranged in front of the evaporator and in parallel with the evaporator,
- provided on the first LNG fuel line (5) between the LNG fuel tank (23) and the second LNG fuel line (13) when the first valve (29) is closed and the second valve The evaporator 22 of the two evaporators 15 and 22 includes a BOG condenser 22 configured to condense the evaporated gas BOG by evaporating the LNG from the LNG fuel tank 23 by heat exchange with the LPG cargo system, Lt; / RTI >
The system for liquefying the LPG evaporation gas (BOG) further comprises at least one refueling unit (100), and the refueling unit (BOG) from the cargo tank (20) Wherein the evaporator (25) is constructed in such a manner that the cargo compressors (40, 41) configured to fully compress and return the refrigerant to the cargo tank (20) as a condensate are disposed in the single stage manner in front of the evaporative gas condenser Is configured to treat excess LNG that has not been evaporated by the condenser (22)
A first LNG fuel line 13 is provided on the first LNG fuel line 5 between the LNG fuel tank 23 and the second LNG fuel line 13 when the first valve 29 is opened and the second valve 30 is closed The evaporator 15 of the two evaporators 15 and 22 is configured to be capable of subcooling the LPG condensate by evaporating the LNG from the fuel tank 23 so that the liquefaction unit 100 and the cargo tank 20 can be cooled, (15) disposed in the condensing line (3) between the condensing line (3) and the condensing line (3). The method according to claim 1,
Characterized in that the return pump is located after the evaporative gas (BOG) condenser and is adapted to transfer the condensed evaporated gas (BOG) to the cargo tank (20). A second LNG fuel line 13 connected in series to the first LNG fuel line 5 downstream of the at least one LNG fuel tank 23, the first LNG fuel line 5 and the first LNG fuel line 5, An LNG fuel supply system comprising: A system comprising an LPG cargo system comprising at least one LPG cargo tank (20), at least one refueling line (100) provided with an evaporation gas line (1) and a condensate line (3) BOG) is liquefied,
- two evaporators (22, 15) located on the first LNG fuel line (5) between the LNG fuel tank and the second LNG fuel line (13) and two evaporators Providing at least one evaporator (25) disposed downstream;
Condensing the evaporated gas by evaporating the LNG flowing from the LNG fuel tank;
Arranging said cargo compressors arranged in a single stage manner in front of cargo compressors (40, 41), evaporation gas (BOG) condensers of at least one refueling unit (100) The gas BOG is sufficiently compressed and transported back to the cargo tank 20 as a condensate; And
≪ / RTI > wherein the condensed evaporated gas is sent to the LPG cargo tank. The method of claim 3,
Wherein the LNG flow from the LNG fuel tank (23) is free flowing, the method further comprising providing a return pump after the evaporative gas condenser, the return pump delivering the condensed evaporative gas to the LPG cargo To the tank (20). ≪ Desc / Clms Page number 13 > The method of claim 3,
- the residual LNG from the evaporator (15, 22) is evaporated by the at least one evaporator (25)
- at least one superheater (26) is provided downstream of said at least one evaporator (25)
Wherein the vapor from the at least one evaporator (25) is heated to a desired fuel gas temperature. The method of claim 3,
- providing at least two cargo tanks (20) simultaneously carrying the first and second different cargoes;
The LNG is first evaporated with respect to the first cargo in at least one evaporator 22 and then the evaporated LNG is introduced into line 80 via line 74 on a parallel arranged evaporator 22 operating on the second cargo, Operating the two evaporators (22, 15) in a sequential order so as to flow through the evaporator (22, 15); And
- returning the higher temperature vaporized LNG resulting from said step to said fuel gas system through said first LNG fuel line (5). ≪ Desc / Clms Page number 13 > The method of claim 6,
Wherein the first cargo is propane and the second cargo is butane. delete delete

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