GAS TREATMENT SYSTEM AND SHIP INCLUDING SAME

The present invention relates to a gas treatment system and a ship including the same. The gas treatment system treats liquefied gas as heavier hydrocarbons or ammonia. The gas treatment system includes: a fuel tank storing liquefied gas as a fuel to be supplied to a propulsion engine of a ship; a liquefied gas supply line supplying the liquefied gas of the fuel tank in a liquid phase to the propulsion engine, the liquefied gas supply line having a high pressure pump provided thereon; a reliquefaction apparatus liquefying boil-off gas generated in a cargo tank storing liquefied gas; and a liquefied gas collection line collecting the liquid liquefied gas discharged from the propulsion engine upstream of the high pressure pump. The reliquefaction apparatus transfers the liquefied boil-off gas to the fuel tank, thereby allowing the liquefied boil-off gas to be supplied to the propulsion engine by the high pressure pump.

TECHNICAL FIELD

The present invention relates to a gas treatment system and a ship including the same.

BACKGROUND ART

In general, Liquefied Petroleum Gas (LPG) is obtained by pressurizing and liquefying a gas using, as a main component, hydrocarbon having a low boiling point, such as propane or butane, among petroleum components. The LPG is charged in a small, light pressure vessel (bombe) to be widely used as a fuel for household use, business use, industrial use, vehicle use, and the like.

The LPG is extracted in a gaseous state from a production area, is liquefied and stored through LPG treatment facilities, is transported by land while being maintained in a liquid phase by an LPG carrier, and then is supplied in various forms to sources of demand.

Since the LPG has a boiling point of about −50° C., an LPG carrier for carrying the LPG should maintain a temperature lower than the boiling point. Therefore, a storage tank for storing the LPG uses low temperature carbon steel and nickel steel, and reliquefaction facilities are also provided in the LPG carrier.

The LPG carrier conventionally operated an engine, using diesel oil, thereby generating propulsion. However, the diesel oil generates nitrogen oxide (NOx), sulfur oxide (SOx), and carbon dioxide (CO2), which are harmful components, in a process in which the diesel oil is burned in an engine for ship propulsion, and the harmful components are discharged in the air. Therefore, there is a problem of contaminating environments.

Accordingly, recently, development of an engine operated using the LPG and development of various systems for supplying the LPG to the engine have continuously conducted to remarkably reduce the pollution of exhaust, as compared with when the diesel oil is used.

DISCLOSURE

Technical Problem

The present invention is conceived to solve the aforementioned problems. Accordingly, an object of the present invention is to provide a gas treatment system and a ship including the same, which can generate propulsion by using liquefied petroleum gas or ammonia.

Technical Solution

In accordance with an aspect of the present invention, there is provided a gas treatment system for treating liquefied gas as heavier hydrocarbons or ammonia, the gas treatment system including: a fuel tank storing liquefied gas as a fuel to be supplied to a propulsion engine of a ship; a liquefied gas supply line supplying the liquefied gas of the fuel tank in a liquid phase to the propulsion engine, the liquefied gas supply line having a high pressure pump provided thereon; a reliquefaction apparatus liquefying boil-off gas generated in a cargo tank storing liquefied gas; and a liquefied gas collection line collecting the liquid liquefied gas discharged from the propulsion engine upstream of the high pressure pump, wherein the reliquefaction apparatus transfers the liquefied boil-off gas to the fuel tank, thereby allowing the liquefied boil-off gas to be supplied to the propulsion engine by the high pressure pump.

Specifically, the liquefied gas collection line may be provided with a decompression valve decompressing surplus liquid liquefied gas which is discharged from the propulsion engine and is mixed with a lubricant, and transfer the surplus liquid liquefied gas mixed with the lubricant, which is used in the propulsion engine, to the liquefied gas supply line upstream of the high pressure pump while passing through the inside of the propulsion engine such that the surplus liquid liquefied gas mixed with the lubricant is reintroduced into the propulsion engine.

Specifically, the liquefied gas collection line may be provided with a cooler cooling the liquefied gas decompressed by the decompression valve to be introduced in a liquid phase into the high pressure pump.

Specifically, the reliquefaction apparatus may include: a compressor compressing in multiple stages the boil-off gas discharged from the cargo tank; a condenser cooling an liquefying the compressed boil-off gas by using a refrigerant; and an intercooler heat-exchanging a portion and the other portion of the boil-off gas liquefied in the condenser with each other, the intercooler transferring the boil-off gas generated by the heat exchange to the compressor.

Specifically, the reliquefaction apparatus may further include a gas-liquid separator separating the boil-off gas liquefied in the condenser into a gaseous phase and a liquid phase. The reliquefaction apparatus may be operated in at least one of a reliquefaction mode in which the liquid phase separated in the gas-liquid separator is transferred to the cargo tank via the intercooler and a fuel supply mode in which the liquid phase separated in the gas-liquid separator is transferred to the fuel tank to be supplied to the propulsion engine.

Specifically, the reliquefaction apparatus may include: a compressor compressing in multiple stages the boil-off gas discharged from the cargo tank; a condenser cooling and liquefying the compressed boil-off gas; and a boil-off gas heat exchanger heat-exchanging boil-off gas transferred from the cargo tank to the compressor and the boil-off gas liquefied in the condenser.

Specifically, the reliquefaction apparatus may further include a gas-liquid separator separating the boil-off gas liquefied in the condenser into a gaseous phase and a liquid phase. The reliquefaction apparatus may be operated in at least one of a reliquefaction mode in which the liquid phase separated in the gas-liquid separator is transferred to the cargo tank via the boil-off gas heat exchanger and a fuel supply mode in which the liquid phase separated in the gas-liquid separator is transferred to the fuel tank to be supplied to the propulsion engine.

In accordance with another aspect of the present invention, there is provided a gas treatment system for treating liquefied gas as heavier hydrocarbons or ammonia, the gas treatment system including: a liquefied gas supply line supplying liquefied gas stored in a cargo tank in a liquid phase to a propulsion engine, the liquefied gas supply line being provided with a high pressure pump; a reliquefaction apparatus liquefying boil-off gas generated in the cargo tank such that the liquefied boil-off gas is transferred to the high pressure pump; and a liquefied gas collection line collecting the liquid liquefied gas discharged from the propulsion engine upstream of the high pressure pump, wherein the reliquefaction apparatus includes: a condenser cooling and liquefying boil-off gas by using a refrigerant; and a buffer temporarily storing the boil-off gas liquefied in the condenser, and wherein the reliquefaction apparatus has a bypass line allows at least a portion of the boil-off gas to be supplied to the buffer while bypassing the condenser so as to prepare for fluctuation of the pressure of boil-off gas transferred from the buffer to the high pressure pump according to a temperature of the refrigerant.

Specifically, the liquefied gas collection line may be provided with a decompression valve decompressing surplus liquid liquefied gas which is discharged from the propulsion engine and is mixed with a lubricant, and transfer the surplus liquid liquefied gas mixed with the lubricant, which is used in the propulsion engine, to the liquefied gas supply line upstream of the high pressure pump while passing through the inside of the propulsion engine such that the surplus liquid liquefied gas mixed with the lubricant is reintroduced into the propulsion engine.

Specifically, the liquefied gas collection line may be provided with a cooler cooling the liquefied gas decompressed by the decompression valve to be introduced in a liquid phase into the high pressure pump.

Specifically, the buffer may be a gas-liquid separator separating the boil-off gas liquefied in the condenser into a gaseous phase and a liquid phase.

Specifically, the reliquefaction apparatus may transfer the liquefied boil-off gas to the liquefied gas supply line between the cargo tank and the high pressure pump.

Specifically, the reliquefaction apparatus may include: a compressor compressing in multiple stages the boil-off gas discharged from the cargo tank; and an intercooler heat-exchanging a portion and the other portion of the boil-off gas liquefied in the condenser with each other, the intercooler transferring the boil-off gas generated by the heat exchange to the compressor.

Specifically, the reliquefaction apparatus may be operated in at least one of a reliquefaction mode in which the liquid phase separated in the gas-liquid separator is transferred to the cargo tank via the intercooler and a fuel supply mode in which the liquid phase separated in the gas-liquid separator is transferred to the liquefied gas supply line upstream of the high pressure pump to be supplied to the propulsion engine.

In accordance with still another aspect of the present invention, there is provided a liquefied gas carrier including the gas treatment system.

Advantageous Effects

In the gas treatment system and the ship including the same in accordance with the present invention, liquefied petroleum gas or ammonia can be used as a propulsion fuel, as compared with conventional systems using only diesel oil. Thus, environmental pollution can be reduced, and energy efficiency can be improved.

MODE FOR THE INVENTION

Hereinafter, exemplary embodiments are described in detail with reference to the accompanying drawings. For reference, in this specification, liquefied gas may be, as heavier hydrocarbons, LPG (propane, butane or the like), ammonia, or the like. However, the present invention is not limited thereto, and the liquefied gas may include all materials which have boiling points lower than room temperature and have caloric values.

Also, in this specification, it is noted that liquefied gas/boil-off gas is not necessarily limited to a liquid phase or a gaseous phase.

The present invention includes a ship in which a gas treatment system described below. The ship is a concept including all of gas carriers, merchant ships for carrying cargos or people instead of gas, FSRUs, FPSOs, bunkering vessels, offshore plants, and the like, but it is noted that the ship may be a liquefied gas carrier as an example.

Although not shown in drawings of the present invention, it will be apparent that a pressure sensor (PT), a temperature sensor (TT), and the like may be provided at appropriate positions without limiting, and a value measured by each sensor may be variously used without limiting to operations of components described below.

FIG.1is a conceptual view illustrating a gas treatment system in accordance with a first embodiment of the present invention.

Referring toFIG.1, the gas treatment system1in accordance with the first embodiment of the present invention includes a gas storage part, a fuel supply part20, a reliquefaction part30, and a fuel collection part40.

The gas storage is a component for storing liquefied gas, and includes a cargo tank10, a fuel tank12, and the like.

The cargo tank10corresponds to a plurality of tanks for cargos, which are provided inside a ship. When the ship is a kind of ship except the gas carrier, the cargo tank10may also be a tank or a container, which is additionally added to the inside or outside of the ship.

The cargo tank10is a tank for storing liquefied gas in a low temperature liquid phase at atmospheric pressure, and various heat insulated structures may be added to a wall structure of the cargo tank10so as to prevent boil off of the liquefied gas. Also, the cargo tank10may be a membrane-type tank, an independence-type tank, or the like, and its shape, resource, or the like is not limited.

A liquefied gas transfer line L21may be provided from the cargo tank10to the fuel tank12which will be described later, and the liquefied gas of the cargo tank10is transferred to the fuel tank12through the liquefied gas transfer line L21. The liquefied gas transferred to the fuel tank12is used as a fuel of a propulsion engine E.

For reference, in this specification, the propulsion engine E is sufficient as long as it is a component for propelling the ship, and may be construed as all components capable of directly/indirectly generating propulsion by consuming the liquefied gas, such as a turbine and a fuel cell instead of engines. Also, in this specification, the propulsion engine E may be used as a term including all gas sources of demand, such as an engine for propulsion, an engine for power generation, and a gas combustion apparatus.

A transfer pump11may be allocated to the cargo tank10, and the liquefied gas transfer line L21may be connected to the transfer pump11. The transfer pump11may be provided inside the cargo tank10, and be provided as a submerged type pump submerged in the liquefied gas.

The transfer pump11may be provided in some of the plurality of cargo tanks10. The cargo tank10is basically for the purpose of cargo transportation, and at least two cargo pumps (loading/unloading pumps, stripping pump, or the like (not shown)) for unloading cargos for each cargo tank10. In addition to the cargo pump, the transfer pump11may be added to at least one cargo tank10so as to use the liquefied gas stored inside the cargo tank10as a fuel of the propulsion engine E (ME-LGI), or the like.

In an example, when four cargo tanks10are provided side by side in a length direction of the ship, the liquefied gas stored in a fourth cargo tank10close to an engine room in which the propulsion engine E is accommodated may be transferred to the fuel tank12and then be used as the fuel of the propulsion engine E. To this end, the transfer pump11may be provided in only the fourth cargo tank10.

The liquefied gas stored in the cargo tank10is naturally boiled off by external heat infiltration, and therefore, boil-off gas is generated in the cargo tank10. A boil-off gas discharge line L10for discharging the boil-off gas may be provided in the cargo tank10. The boil-off gas discharged from the cargo tank10may be liquefied and then returned or be used as the fuel of the propulsion engine E. This will be described in detail at a portion at which the reliquefaction part30is described below.

The cargo tank10may be provided in plurality to respectively store at least two kinds of liquefied gases among liquefied gases (propane, butane, propylene, and the like) using heavier hydrocarbons as a main component. That is, the cargo tank10may include a first cargo tank10for storing a first kind of liquefied gas and a second cargo tank10for storing a second kind of liquefied gas. In an example, the first cargo tank10may store propane, and the second cargo tank10may store butane or the like.

The boil-off gas of the cargo tank10is liquefied through a condenser32of the reliquefaction part30which will be described later. When the liquefied boil-off gas is configured to be returned to the cargo tank10, the condenser32may be provided as many as kinds of liquefied gases stored in the at least the cargo tank10(additionally, a condenser for backup may be provided).

That is, when the cargo tank10stores two kinds of liquefied gases, at least three condensers320may be preferably provided. In addition, a compressor31along with the condenser32is provided as a set. Hence, the compressor31may be provided in plurality to correspond to the number of condensers32.

However, in this embodiment, the boil-off gas liquefied by the condenser32is not returned to the cargo tank10but may be transferred to the fuel tank12or the like, so that although the cargo tank10is provided to store two or more kinds of liquefied gases, the number of condensers32installed (or operated) can be decreased equal to or smaller than the number of kinds of liquefied gases.

That is, the boil-off gas of the cargo tank10may be transferred to the condenser320through the boil-off gas discharge line L10to be liquefied by refrigerant heat exchange in the condenser32, and the liquefied boil-off gas may be transferred to a high pressure pump22which will be described later via the fuel tank12but may not be returned to the cargo tank10(fuel supply mode).

The fuel tank12stores the liquefied gas as the fuel to be supplied to the propulsion engine E. The fuel tank12may have a type identical to or different from the type of the cargo tank10which has an independence type (SPB type or MOSS type) where a large amount of liquefied gas is stored at atmospheric pressure or a membrane type, and have an independence type (Type C or pressure container type) where liquefied gas is stored at high pressure.

The fuel tank12may store the liquefied gas at a critical pressure or higher (e.g., 18 bars or so) or store the liquefied gas at less than the critical pressure (e.g., 8 bars or so). A heat insulated structure may be provided on at least one of the inside or outside of the wall structure so as to prevent boil off of the liquefied gas.

The fuel tank12may be mounted on an upper deck in the ship, and be provided to be supported by the upper deck through a saddle. The fuel tank12may be disposed at a position at which sailing visibility of the ship is covered while being interfered with components (manifold and the like) for loading/unloading the liquefied gas of the cargo tank10on the upper deck. In an example, the fuel tank12may be provided at a portside or a starboard of a bow on the upper deck. The fuel tank12may be designated as a deck tank.

The fuel tank12may be a component for temporarily storing the liquefied gas between the cargo tank10and the propulsion engine E. Also, the fuel tank12may be a component which has a function of condensing the boil-off gas generated in the cargo tank10by using the liquefied gas stored thereinside.

That is, the fuel tank12may be used as a recondenser32for receiving and condensing the boil-off gas generated in the cargo tank10by using the liquefied gas stored thereinside. To this end, a boil-off branch line (not shown) branching off toward the fuel tank12upstream of the condenser32may be provided on the boil-off gas discharge line L10extending from the cargo tank10.

The described-above liquefied gas transfer line L21may be connected from the cargo tank10to the fuel tank12, and the liquefied gas may be transferred to the fuel tank12by the transfer pump11submerged in the cargo tank10. The liquefied gas stored in the fuel tank12may be manages at an appropriate level/pressure by considering a sailing state of the ship, and the like.

On the contrary, the liquefied gas may be returned from the fuel tank12to the cargo tank10, but this may be limited to a case where the liquefied gas stored in the fuel tank12have the same composition as the liquefied gas stored in the cargo tank10.

The liquefied gas stored in the fuel tank12may be transferred from the fuel tank12to the propulsion engine E through a low pressure pump of the fuel supply part20which will be described later. A liquefied gas supply line L20may be provided from the fuel tank12to the propulsion engine E. That is, the liquefied gas transfer line L21is provided from the cargo tank10to the fuel tank12, and the liquefied gas supply line L20is provided from the fuel tank12to the propulsion engine E.

The liquefied gas supply line L20may also be provided such that the liquefied gas is supplied from the cargo tank10to the propulsion engine E while bypassing the fuel tank12. In this case, the liquefied gas supply line L20may transfer the liquefied gas of the cargo tank10and/or the fuel tank12to the propulsion engine E.

The fuel supply part20supplies the liquefied gas to the propulsion engine E, thereby operating the propulsion engine E. The fuel supply part20includes the low pressure pump21, the high pressure pump22, a heat exchanger23, and the like, and a filter (reference numeral not shown) may be provided at an appropriate position.

The low pressure pump21transfers the liquefied gas of the fuel tank12to the propulsion engine E. The low pressure pump21may be provided at the inside or outside of the fuel tank12, and be provided on the liquefied gas supply line L20connected from the fuel tank12to the propulsion engine E.

The low pressure pump21may pressurize the liquefied gas at a pressure lower than a required pressure of the propulsion engine E. Specifically, the low pressure pump21may pressurize the liquefied gas to be suitable for a suction pressure (e.g., 20 bars) of the high pressure pump22disposed downstream of the low pressure pump21. That is, the low pressure pump21increases the pressure of the liquefied gas by a difference pressure between an internal pressure of the fuel tank12and the suction pressure of the high pressure pump22.

However, when a storage pressure of the fuel tank12corresponds to the suction pressure of the high pressure pump22, the low pressure pump21may be omitted.

A liquefied gas return line (not shown) may be provided downstream of the low pressure pump21on the liquefied gas supply line L20. When a flow volume transferred to the propulsion engine E through the low pressure pump21exceeds a required flow volume of the propulsion engine E, the liquefied gas return line may function to collect surplus liquefied gas in the fuel tank12.

Alternatively, the liquefied gas return line allows the liquefied gas which is discharged from the fuel tank12and then is pressurized by the low pressure pump21to be reintroduced into the fuel tank12, so that a function of increasing the internal pressure of the fuel tank12can be implemented. Thus, the fuel tank12maintains the internal pressure to become high, thereby minimizing occurrence of boil-off gas in the fuel tank12.

The high pressure pump22pressurizes the liquefied gas of the fuel tank12, corresponding to the required pressure of the propulsion engine E, and transfers the pressurized liquefied gas to the propulsion engine E. The required pressure of the propulsion engine E may be 20 to 50 bars, but be changed according to resources of the propulsion engine E.

The high pressure pump22is provided on the liquefied gas supply line L20extending from the fuel tank12to the propulsion engine E. The type of the high pressure pump22is not particularly limited, and a plurality of high pressure pumps22may be provided in parallel to back up each other as shown in the drawing.

The high pressure pump22may be provided upstream of the heat exchanger23which will be described later as shown in the drawing, or be provided downstream of the heat exchanger23, unlike the drawing. In the latter case, the high pressure pump22may pressurize the liquefied gas of which temperature is adjusted by the heat exchanger23to a pressure which the propulsion engine E requires.

In order to suppress occurrence of cavitation in a liquefied gas pressurization process, the liquefied gas may be introduced in a liquid phase into the high pressure pump22. When the heat exchanger23is provided upstream of the high pressure pump22, the heat exchanger may control the temperature of the liquefied gas by considering the above-described items.

A pressure of the liquefied gas sucked into the high pressure pump22may correspond to a pressure of the liquefied gas discharged by the low pressure pump21. Also, the pressure of the liquefied gas sucked into the high pressure pump22may also correspond to a pressure of the liquefied gas collected in the propulsion engine E.

A filter (reference numeral not shown) for filtering an impurity may be provided downstream of the high pressure pump22. The filter may be additionally provided upstream of the low pressure pump21, or the like as shown in the drawing.

In addition, a fuel supply valve (not shown) may be provided downstream of the high pressure pump22on the liquefied gas supply line L20. The fuel supply valve and a decompression valve (not shown) provided on a liquefied gas collection line L30may be configured as one train to be designated as a FVT (fuel valve train).

A liquefied gas circulation line L22connected to the liquefied gas collection line L30of the fuel collection part40which will be described later may be provided on the liquefied supply line L20downstream of the high pressure pump22. The liquefied gas discharged from the high pressure pump22is transferred to the liquefied gas collection line L30along the liquefied gas circulation line L22, to be again circulated to the high pressure pump22.

A minimum required flow volume of the high pressure pump22is set for the purpose of operational stability, and the like. This is referred to as minimum flow, and the liquefied gas satisfying the minimum required flow volume may be preferably introduced into the high pressure pump22in an operation.

However, there is a case where a consumption volume in the propulsion engine E downstream of the high pressure22, and the like does not satisfy the minimum required flow volume. In an example, there is a case where the propulsion engine E is operated with a low load, or the operation is stopped in a situation in which the high pressure pump22is under operation, or the like.

In this embodiment, in order to stably operate the high pressure pump22, the liquefied gas may be circulated such that the liquefied gas having the minimum required flow volume or more is introduced into the high pressure pump22even when the required flow volume of the propulsion engine E is short of the minimum required flow volume of the high pressure pump22.

That is, when the minimum required flow volume of the high pressure pump22is 100 and the required flow volume of the propulsion engine E is 80, the liquefied gas of20may be circulated to the high pressure pump22via the liquefied gas circulation line L22and the liquefied gas collection line L30downstream of the high pressure pump22.

Thus, when the required flow volume of the propulsion engine E is equal to or smaller than the minimum required flow volume of the high pressure pump22, the liquefied gas circulation line L22circulates the liquefied gas having a flow volume or more except the required flow volume of the propulsion engine E with respect to the minimum required flow volume of the high pressure pump22, thereby guaranteeing the minimum required flow volume of the high pressure pump22.

The heat exchanger23is provided downstream of the low pressure pump21to change the temperature of the liquefied gas. The heat exchanger23may increase or decrease the temperature of the liquefied gas. Therefore, the heat exchanger23may be designated as a fuel conditioner.

In an example, in an initial operation of this embodiment, the flow volume of high temperature liquefied gas is large, and hence the heat exchanger23may decrease the temperature of the liquefied gas. In a stable operation, the heat exchanger23may increase the temperature of the liquefied gas.

The heat exchanger23may be provided downstream of the high pressure pump22as shown in the drawing. Unlike the drawing, the heat exchanger23may be provided upstream of the high pressure pump23. In the latter case, the heat exchanger23may control the temperature of the liquefied gas to be equal to or lower than the boiling point of the liquefied gas such that gaseous liquefied gas is not introduced into the high pressure pump22.

The heat exchanger23may implement heat exchange with the liquefied gas by using various heat exchange media. In an example, the heat exchange media may be seawater, purified water, glycol water, exhaust, and the like, but the present invention is not limited thereto.

The reliquefaction part30liquefies boil-off gas generated in the cargo tank10. The reliquefaction part30may be configured as a module in which several components are disposed on one skid to constitute a reliquefaction apparatus. The reliquefaction part30may include a plurality of reliquefaction apparatuses. However, for convenience, one reliquefaction apparatus is illustrated in the drawing.

The reliquefaction apparatus includes the compressor31, the condenser32, a gas-liquid separator33, an intercooler34, and an aftercooler35. The compressor31, the aftercooler35, the condenser32, and the gas-liquid separator33may be sequentially disposed in series on the boil-off discharge line L10, and the intercooler34may be provided on a boil-off gas return line L11connected from the gas-liquid separator33to the cargo tank10.

The compressor31compresses the boil-off gas discharged from the cargo tank10. The compressor31may allow the boiling point of the boil-off gas to be increased by compression, and accordingly, the liquefaction efficiency in the condenser32described below can be improved.

The compressor31may be configured in multiple stages, and be provided in three stages as shown in the drawing or be provided in various stages. Also, the compressor31may be provided in parallel on the boil-off gas discharge line L10to back up each other.

The compressor31may transfer the compressed boil-off gas to the condenser32such that the compressed boil-off gas is liquefied, or transfer the compressed boil-off gas to the fuel tank12filled with an appropriate volume of liquefied gas. In the former case, the boil-off gas liquefied in the condenser32may be supplied to the fuel tank12. In the latter case, the high-pressure boil-off gas may be directly injected into the fuel tank12and be cooled and liquefied by the liquefied gas in the fuel tank12.

A drum (not shown) may be provided upstream of the compressor31. The drum is a gas-liquid separation component for filtering droplets in the boil-off gas discharged from the cargo tank10, and the droplets may be provided to be returned to the cargo tank10.

The drum allows any droplets not to be introduced into the compressor31, thereby protecting the compressor31. The drum may be omitted according to a type of the compressor31.

The condenser32liquefies the boil-off gas generated in the cargo tank10. The liquefaction of the boil-off gas may use a refrigerant, and the refrigerant may be glycol water, nitrogen, seawater, or the like. However, hereinafter, in this specification, it is assumed and described that the refrigerant of the condenser32is seawater.

The condenser32may have two stream structures including a boil-off gas stream along which the boil-off gas compressed in the compressor31is introduced thereinto and a refrigerant stream along which a refrigerant for performing heat exchange with the boil-off gas flows.

The type of the condenser32is not limited, such as Shell & Tube or PCHE, and a bath type where boil-off gas in a housing having a refrigerant stored therein passes to perform heat exchange.

The cargo tank10may be provided in plurality to respectively store at least two kinds of liquefied gases as described above, and the condenser32may be provided to liquefy all of different kinds of boil-off gases.

When a plurality of cargo tanks10for storing different kinds of liquefied gases are provided, a plurality of condensers32may be provided corresponding to kinds of liquefied gases. Alternatively, as described above, in this embodiment, different kinds of boil-off gases are integrally transferred to one condenser32, thereby decreasing the installation number (or operation number) of condensers32.

This is because an operation (fuel supply mode) in which the reliquefaction apparatus of this embodiment transfers the liquefied boil-off gas to the fuel tank12instead of the cargo tank10to be consumed in the propulsion engine E is possible.

When any composition pollution in the cargo tank10does not occur even though the boil-off gas liquefied in the condenser32is returned to the cargo tank10, the reliquefaction apparatus may be operated in a reliquefaction mode in which the liquefied boil-off gas is transferred to the cargo tank10.

The gas-liquid separator33stores the boil-off gas liquefied in the condenser32. The gas-liquid separator33may have a container shape, a shape in which a tube partially extend, or the like to have a function of a buffer.

The gas-liquid separator33may separate the liquefied boil-off gas into a gaseous phase and a liquid phase and then transfer the liquid phase to the cargo tank10, the fuel tank12, or the like. The gas-liquid separator33may transfer only the liquid phase to the cargo tank10or the like, accommodate the gaseous phase thereinside. The gas-liquid separator33maintains an internal pressure to a certain level, so that liquefaction of the boil-off gas can be prevented.

As described above, the reliquefaction apparatus may be operated in the fuel supply mode in which the liquefied boil-off gas is transferred to the fuel tank12instead of the cargo tank10so as to prevent composition mixture of the liquefied gas (or to supply the boil-off gas to the propulsion engine E). To this end, the gas-liquid separator33may be provided with a boil-off gas transfer line L12for transferring the liquid phase to the fuel tank12.

Alternatively, in order for the reliquefaction apparatus to be operated in the reliquefaction mode, the boil-off gas return line L11may be provided toward the cargo tank10from the gas-liquid separator33, and the intercooler34may be provided on the boil-off gas return line L11.

Therefore, the reliquefaction apparatus may be operated in at least one of the reliquefaction mode in which the liquid phase separated in the gas-liquid separator33is transferred to the cargo tank10via the intercooler34and/or the fuel supply mode in which the liquid phase separated in the gas-liquid separator33is transferred to the fuel tank12to be supplied to the propulsion engine E.

That is, the reliquefaction apparatus may be operated in a mode obtained by combining the reliquefaction mode and the fuel supply mode. In the combination mode, a portion of is transferred to the cargo tank10, and the other of the liquid phase separated in the gas-liquid separator33is transferred to the fuel tank12. The flow volume of the liquid phase branching off to the fuel tank12may be controlled according to a load of the propulsion engine E.

The intercooler34heat-exchanges a portion and the other of the boil-off gas liquefied in the condenser32with each other, and transfers, to the compressor31, a gaseous boil-off gas generated by the heat exchange in the boil-off gas introduced from the condenser32.

The intercooler34is used to cool the boil-off gas in a middle stage of the compressor31configured in multiple stages. When the boil-off gas is compressed by the compressor31, the temperature of the boil-off gas is increased due to compression heat. In this case, there is a problem that a load of the compressor31increases. Therefore, in this embodiment, the intercooler34may be used for middle cooling.

Specifically, the intercooler34is provided in a container shape for storing a portion of the boil-off gas liquefied in the condenser32, and the boil-off gas stored inside the intercooler34is used as a refrigerant for cooling the other (flow volume transferred to the cargo tank10) of the boil-off gas liquefied in the condenser32.

To this end, the boil-off gas return line L11branches off upstream of the intercooler34. One side of the boil-off gas return line L11transfers the boil-off gas into the intercooler34, and the other side of the boil-off gas return line L11is connected to the cargo tank10via the inside of the intercooler34to perform heat exchange with the boil-off gas stored in the intercooler34.

That is, the intercooler34may sufficiently liquefy the boil-off gas transferred to the cargo tank10by heat-exchanging the boil-off gas transferred from the condenser32to the cargo tank10with the boil-off gas which is transferred from the condenser and then stored thereinside.

A portion of the boil-off gas return line L11, which passes through the inside of the intercooler34, may be provided in a coil shape so as to improve heat exchange efficiency. In addition, a decompression valve (reference numeral not shown) may be provided at a portion of the boil-off gas return line L11, which transfers the boil-off gas to the inside of the intercooler34.

Also, the intercooler34may transfer a gaseous phase in the boil-off gas stored thereinside to a middle stage of the compressor31. The gaseous boil-off gas transferred to the middle stage of the compressor31is in an extremely low temperature state close to the boiling point. Therefore, the boil-off gas in the middle stage of the compressor31may be cooled while being mixed with the gaseous boil-off gas transferred from the intercooler34.

The intercooler34may be allocated to each middle stage of the compressor32configured in multiple stages. However, since the boil-off gas is circulated by the intercooler34, a boil-off gas volume which may be introduced from the cargo tank10to the reliquefaction apparatus may be limited due to a boil-off gas volume transferred from the intercooler34to the middle stage of the compressor31.

That is, the reliquefaction apparatus has a reliquefaction volume obtained by subtracting the boil-off gas volume transferred to the middle stage of the compressor31by the intercooler34from an introduction allow volume of a first stage of the compressor31. In an example, when the introduction allow volume of the first stage of the compressor31is 800, a boil-off gas volume of 200 is circulated in a middle stage (between first and second stages and between second and third stages) of the compressor31by the intercooler34. Finally, the boil-off gas volume which the reliquefaction apparatus can receive from the cargo tank10is decreased to 400.

In order to solve this, in this embodiment, the intercooler34is allocated to only some of middle stages of the compressor31, and the aftercooler35instead of the intercooler34is provided to the others of the middle stages of the compressor31, so that the volume of the reliquefaction apparatus can be increased.

The intercooler34may be replaced with a separator. Similarly to the gas-liquid separator33described above, the separator may separate the boil-off gas liquefied in the condenser32into a gaseous phase and a liquid phase. The separator may transfer the liquid phase to the cargo tank10, and transfer the gaseous phase to the middle stage of the compressor31. In this case, the separator simply separates the boil-off gas into the gaseous phase and the liquid phase, and does not implement heat exchange between boil-off gases. Therefore, the boil-off gas return line L11having a coil shape may be omitted inside the separator.

The aftercooler35may be provided in some of the middle stages of the compressor31and cool the boil-off gas by using a separate refrigerant. The aftercooler35may implement a function of a precooler from the viewpoint of the condenser32.

Similarly to the condenser32, the aftercooler35may use a refrigerant such as seawater. In addition, the aftercooler35may use various refrigerants. However, the aftercooler35may use a separate refrigerant supplied from the outside instead of the liquefied gas stored in the cargo tank10or the boil-off gas discharged from the cargo tank10.

When describing with reference to the drawing, in this embodiment, the gaseous boil-off gas may be circulated by connecting the intercooler34between the first and second stages of the compressor31, and the aftercooler35may be provided between the second and third stages of the compressor31.

When the introduction allow volume of the first stage of the compressor31is 800 and the circulation of the intercooler34is made by a boil-off gas volume of 200, in this embodiment, a boil-off gas volume of 600 is allowed to be transferred from the cargo tank10to the reliquefaction apparatus.

That is, in this embodiment, as compared with when the reliquefaction apparatus connects the intercooler34to each middle stage of the compressor31, at least one intercooler34is replaced with the aftercooler35, thereby increasing the reliquefaction volume.

The reliquefaction part30of this embodiment may be operated in two modes. In an example, the reliquefaction part30may be operated in a reliquefaction mode in which the boil-off gas liquefied in the condenser32is transferred to the cargo tank10via the intercooler34and a fuel supply mode in which the boil-off gas is transferred toward the propulsion engine E upstream or downstream of the condenser32.

Specifically, in the reliquefaction mode, the multi-stage compressed boil-off gas is liquefied via the condenser32, and then is transferred to the intercooler34while passing through the gas-liquid separator33. The boil-off gas branches off upstream of the intercooler34. A portion of the boil-off gas may be filled inside the intercooler34, and the other of the boil-off gas is not mixed with the boil-off gas filled inside the intercooler34but may pass through the inside of the intercooler34to perform only heat exchange. The boil-off gas passing through the intercooler34may be cooled or supercooled to stably maintain a liquid phase, and then be returned to the cargo tank10.

On the other hand, in the fuel supply mode, the multi-stage compressed boil-off gas may be transferred to the fuel tank12upstream of the condenser32. Alternatively, the multi-stage compressed and condensed boil-off gas may be transferred to the fuel tank12to be transferred to the propulsion engine E by the high pressure pump22.

The fuel supply mode may be made when it is not preferable that the liquefied boil-off gas is returned to the cargo tank10, when only the liquefied gas stored in the fuel tank12does not satisfy a required flow volume of the propulsion engine E since the load of the propulsion engine E is high, or the like.

In an example, when propane and butane are stored in the cargo tank10, the butane may be liquefied by using another reliquefaction apparatus for treating propane, when an operation of a reliquefaction apparatus for treating butane is stopped due to occurrence of a problem. Propane remaining in the reliquefaction apparatus for treating propane may be mixed with butane, and therefore, the fuel supply mode may be made, in which liquefied butane is not transferred to the cargo tank10but transferred to the fuel tank12.

In addition, in various situations in which transfer to the fuel tank12or the like is more preferable than transfer to the cargo tank10, the fuel supply mode may be made instead of the reliquefaction mode. Also, it will be apparent that a combination mode obtained by combining the reliquefaction mode and the fuel supply mode may be made as described above.

The fuel collection part40collects liquid liquefied gas discharged from the propulsion engine E. The fuel collection part40may collect the liquid liquefied gas upstream of the high pressure pump22. To this end, the liquefied gas collection line L30is provided from the propulsion engine E to the liquefied gas supply line L20upstream of the high pressure pump22.

Unlike commercial engines (ME-GI, XDF, and the like) supplied with LNG in a gaseous phase to be consumed, the propulsion engine E (ME-LGI or the like) in the present invention has a structure which discharges surplus liquid fuel while being supplied with LPG or the like in a liquid phase to be consumed.

This is because, unlike the gaseous phase, it is not easy to finely control a fuel supply volume in the liquid phase, and therefore, surplus fuel is generated as the propulsion engine E is supplied with a sufficient volume of liquid fuel.

However, liquefied gas collected in the propulsion engine E is not liquefied gas before being introduced into the propulsion engine E but liquefied gas passing through the inside of the propulsion engine E, and is in a state having a temperature/pressure corresponding to the required pressure of the propulsion engine E (e.g., 45 bars or so and 50° C. or higher). A lubricant used in the propulsion engine E may be mixed inside the liquefied gas.

That is, since the lubricant is mixed with the surplus liquefied gas collected from the propulsion engine E, it is preferable that the collected liquefied gas is not transferred to the cargo tank10so as to prevent cargo pollution.

Therefore, the liquefied gas collection line L30connected to the propulsion engine E to collect surplus liquefied gas may transfer surplus liquefied gas returned from the propulsion engine E to the high pressure pump22instead of the cargo tank10, thereby allowing the surplus liquefied gas to be reintroduced into the propulsion engine E.

That is, the liquefied gas collection line L30transfers the surplus liquid liquefied gas mixed with the lubricant used in the propulsion engine E while passing through the inside of the propulsion engine E to the liquefied gas supply line L30upstream of the high pressure pump22, thereby allowing the surplus liquid liquefied gas to be reintroduced into the propulsion engine E. Accordingly, the liquefied gas in the cargo tank10can be prevented from being polluted due to the lubricant.

The fuel collection part40includes a decompression valve provided on the liquefied gas collection line L30and a cooler41, and may further include a capture tank42and a knockout drum43.

The decompression valve decompresses the surplus liquid liquefied gas which is discharged from the propulsion engine E and is mixed with the lubricant. The decompression valve may be a Joule-Thomson valve. The decompression valve along with the fuel supply valve may constitute a fuel valve train (FVT).

The decompression valve may decompress liquefied gas having a high pressure (about 30 to 50 bars), which is collected in the propulsion engine E, thereby adjusting the pressure of the liquefied gas to the suction pressure of the high pressure pump22.

The cooler41cools the liquefied gas decompressed by the decompression valve on the liquefied gas collection line L30to allow the liquefied gas in a liquid phase to be introduced into the high pressure pump22. The cooler41may use various refrigerants which are not limited, and cool the liquefied gas to be equal to or lower than the boiling point of the decompressed liquefied gas. In an example, the cooler41may use seawater as a refrigerant. The heat exchanger23and the cooler41may be integrally connected by one refrigerant supply part.

Cooling of the cooler41may be made by considering mixture with the liquefied gas transferred from the fuel tank12to the high pressure tank22. Therefore, the cooler41may cool the liquefied gas at a temperature slightly higher than the boiling point of the decompressed liquefied gas.

The liquefied gas in the liquid phase (or in a state close to the liquid phase), which is cooled by the cooler41, is mixed upstream of the high pressure pump22in a liquefied gas supply line L20through the liquefied gas collection line L30, and a mixer (not shown) may be provided at a point at which the liquefied gas collection line L30is connected to the liquefied gas supply line L20.

The above-described liquefied gas circulation line L22may branch off from the liquefied gas supply line L20downstream of the high pressure pump22and be connected upstream of the cooler41from the liquefied gas collection line30, to be connected between the propulsion engine E and the cooler41downstream of the high pressure pump22.

The liquefied gas is pumped and heated due to the operation of the high pressure pump22. When the heated liquefied gas is continuously circulated, the temperature of the high pressure pump22may be unnecessarily increased. Hence, this is for the purpose of suppressing the increase in temperature of the high pressure pump22. That is, in this embodiment, the degree of heat generation of the high pressure pump22when the liquefied gas is circulated through the liquefied gas circulation line L22may be limited to a predetermined value or less by using the cooler41.

Thus, the high pressure pump22can continuously pump liquefied gas of a minimum required flow volume or more, and surplus liquefied gas collected by the liquefied gas circulation line L22is circulated to the high pressure pump22via the cooler41. Accordingly, rupture of the high pressure pump22can be prevented.

The capture tank42captures a portion of the liquefied gas returned from the propulsion engine E. The capture tank42may be provided to branch off from the liquefied gas collection line L30connected from the propulsion engine E to the liquefied gas supply line L20upstream of the high pressure pump22, and a liquefied gas capture line L31may extend from the liquefied gas collection line L30to the capture tank42.

The liquefied gas capture line L31may extend from between the decompression valve and the cooler41on the liquefied gas collection line L3to be connected to the capture tank42, and join with the liquefied gas collection line L30upstream of the cooler41from the capture tank42. That is, the liquefied gas capture line L31may be partially provided in parallel to the liquefied gas collection line L30, and be provided such that the capture tank43is provided thereon.

The capture tank42separates the collected liquefied gas into a gaseous phase and a liquid phase. When gaseous liquefied gas is introduced into the high pressure pump22, a cavitation problem may occur. Therefore, in the present invention, the liquefied gas flowing along the liquefied gas collection line L30is separated into the gas phase and the liquid phase while passing through the capture tank42, if necessary, so that introduction of the gaseous liquefied gas into the high pressure pump22can be blocked.

That is, the capture tank42transfers only liquid liquefied gas to the high pressure pump22by capturing the liquefied gas of the liquefied gas collection line L30, so that a stable operation of the high pressure pump22can be ensured.

The knockout drum43may receive liquefied gas collected in the propulsion engine E from the capture tank42, to filter an impurity (lubricant or the like) included in the liquefied gas. A liquefied gas treatment line L32may be connected from the capture tank42to the knockout drum43. The liquefied gas treatment line L32may transfer, to the knockout drum43, the liquid liquefied gas transferred from the capture tank42to the liquefied gas collection line L30, in addition to the gaseous liquefied gas separated in the capture tank42.

The knockout drum42separates lubricant from the liquefied gas introduced thereinto. Specifically, the knockout drum43discharges the liquefied gas in the phase state and discharges the lubricant in the liquid phase. That is, the knockout drum43implements a gas-liquid separation function, similarly to the capture tank42.

However, a heating part such as tracing may be used to accelerate evaporation of the liquefied gas, and the tracing may be a component which uses, as a heat sources, a medium such as steam or seawater or component which performs heating by using electricity.

The knockout drum43heats liquefied gas mixed with lubricant. The liquefied gas may be discharged to a vent mast (not shown), and the lubricant may be treated (recycled) by being drained at a lower portion.

For reference, the vent mast (not shown) discharges, in the air, a material to be vented to the outside between the cargo tank10and the propulsion engine E. The vent mast may be provided on a deck in the ship and have a constant height to protect crewmen on the deck.

It will be apparent that the vent mast may be connected from the capture tank42or the knockout drum43. The vent mast may also be connected to the boil-off gas discharge line L10, the liquefied gas supply line L20, the fuel tank12, and the like. Accordingly, the vent mast implements external discharge in an emergency situation such as a normal operation or suspension of an operation of the propulsion engine E.

Also, the vent mast may discharge, to the outside, purging gas in purging of the boil-off gas discharge line L10, the liquefied gas supply line L20, and the like. The purging gas may be nitrogen gas, inert gas, or the like.

As described above, in this embodiment, boil-off gas generated in the cargo tank10is reliquefied and then transferred to the fuel tank12, to be supplied to the propulsion engine E. Thus, when different kinds of liquefied gases are reliquefied and then returned to the cargo tank10, a problem that liquefied gas compositions may be polluted can be solved, and the number of condensers32installed or operated can be decreased.

FIG.2is a conceptual view illustrating a gas treatment system in accordance with a second embodiment of the present invention.

Hereinafter, in this embodiment, portions different from those of the above-described embodiment will be mainly described, and portions which will not be described below are the same as those of the above-described embodiment. This will be the same as other embodiments which will be described later.

Referring toFIG.2, in the gas treatment system1in accordance with the second embodiment of the present invention, the reliquefaction part30liquefies boil-off gas and transfers the liquefied boil-off gas to the high pressure pump22. Specifically, like the above-described embodiment, the reliquefaction apparatus the liquefied boil-off gas may transfer to the fuel tank12or transfer the liquefied boil-off gas to the liquefied gas supply line L20between the fuel tank12and the high pressure pump22.

To this end, in addition to the boil-off gas return line L11and the boil-off gas transfer line L12, a boil-off gas supply line L13may be provided as a line for transferring a liquid phase separated in the gas-liquid separator33. One end of the boil-off gas supply line L13may extend from the gas-liquid separator33or the boil-off gas transfer line L12, and the other end of the boil-off gas supply line L13may be connected between the high pressure pump22and the low pressure pump21on the liquefied gas supply line L20.

A point at which the boil-off gas transfer line L12is connected to the liquefied gas supply line L20may be upstream of a point at which the liquefied gas collection line L30is connected to the liquefied gas supply line L20or the same point as the point at which the liquefied gas collection line L30is connected to the liquefied gas supply line L20. Therefore, the high pressure pump22may pressurize liquid boil-off gas transferred from the reliquefaction apparatus in addition to liquefied gas supplied from the low pressure pump and surplus liquefied gas collected through the liquefied gas collection line L30, and supply the pressurized gas to the propulsion engine E.

When boil-off gas liquefied in the condenser32is joined with the liquefied gas collected in the liquefied gas collection line L30while bypassing the fuel tank12through the boil-off gas supply line L13and then is supplied to the high pressure pump22, introduction of gas into the high pressure pump22can be still prevented.

Specifically, in this embodiment, an introduction pressure of the high pressure pump22and a boil-off gas pressure (may be an internal pressure of the gas-liquid separator33) downstream of the condenser32are controlled equal to each other, so that a boiling point of the liquefied gas flowing in the liquefied gas supply line L20upstream of the high pressure pump22and a boiling point of the boil-off gas flowing in the boil-off gas supply line L13formed equal to each other. That is, any separate pressurization/compression means is not provided on the boil-off supply line L13between the gas-liquid separator33and the high pressure pump22.

However, the introduction pressure of the high pressure pump22is equal to a pressure downstream of the decompressor valve on the liquefied gas collection line L30. That is, a boiling point of liquid liquefied gas flowing in the liquefied gas collection line L30also becomes equal to the boiling point of the boil-off gas on the boil-off gas supply line L13.

The condenser32of the reliquefaction apparatus and the cooler41on the liquefied gas collection line L30may use the same refrigerant. That is, a refrigerant having the same condition (temperature) is supplied to the condenser32and the cooler41, so that cooling of the boil-off gas/the liquid liquefied gas is implemented at the approximately same temperature.

Thus, in this embodiment, while the cooler41of the fuel collection part40cools liquid liquefied gas having a first pressure by using a first refrigerant to prevent boil-off at an introduction end of the high pressure pump22, the condenser of the reliquefaction part30also cools boil-off gas having the first pressure by using the first refrigerant. Accordingly, the cooler41and the condenser32can be controlled while mutually contacting each other such that any gas is not introduced into the high pressure pump22.

That is, in this embodiment, although the introduction pressure of the high pressure pump22is low, the condenser32condenses boil-off gas by using the same refrigerant as the cooler41with respect to the same pressure as the liquid liquefied gas collected in the fuel collection part40. Thus, although the reliquefaction apparatus directly transfers boil-off gas to the high pressure pump22while bypassing the fuel tank12, the operation stability of the high pressure pump22can be ensured.

Therefore, when the reliquefaction apparatus of this embodiment is operated in the fuel supply mode, the reliquefaction apparatus may not only transfer a liquid phase separated in the gas-liquid separator33to the fuel tank12but also transfer the liquid phase to the liquefied gas supply line L20upstream of the high pressure pump22, to be supplied to the propulsion engine E. The control of flow into the boil-off gas transfer line L12or the boil-off gas supply line L13may be controlled according to various variables including a boil-off gas volume discharged from the cargo tank10, a load of the propulsion engine E, an internal pressure of the fuel tank12, and the like.

Also, the reliquefaction apparatus of this embodiment includes a bypass line L14. The bypass line L14allows at least a portion of boil-off gas to be supplied to the gas-liquid separator33while bypassing the condenser32, and a bypass valve36for flow control may be provided on the bypass line L14.

When the temperature of a refrigerant used by the condenser32is low temperature, boil-off gas may be overcooled by the refrigerant. When the overcooled liquid boil-off gas is introduced into the gas-liquid separator33downstream of the condenser32, a drop of internal pressure of the gas-liquid separator33may be caused.

That is, the temperature of the refrigerant in the condenser32may determine a cooling degree of the boil-off gas, which determines an internal pressure in the gas-liquid separator33. The internal pressure of the gas-liquid separator33may be the pressure of boil-off gas transferred to the high pressure pump through the boil-off gas supply line L13. When the internal pressure of the gas-liquid separator33is low, evaporation of the boil-off gas in the high pressure pump22may be caused as the boiling point of the boil-off gas becomes low.

Therefore, the temperature of the refrigerant of the condenser32may result in a problem of evaporation at the introduction end of the high pressure pump22. Hence, in this embodiment, control of increasing the pressure of the gas-liquid separator33according to the temperature of the refrigerant may be implemented.

To this end, the bypass line L14may allow at least a portion of the boil-off gas to be supplied to the gas-liquid separator33while bypassing the condenser32through opening of the bypass valve36so as to prepare for fluctuation of the pressure of boil-off gas transferred from the gas-liquid separator33to the high pressure pump22according to the temperature of the refrigerant.

When high-temperature, gaseous boil-off gas bypassing the condenser32is introduced into the gas-liquid separator33, the internal pressure of the gas-liquid separator33is increased, and hence the pressure of liquid boil-off gas transferred from the gas-liquid separator33to the liquefied gas supply line L20through the boil-off gas supply line L13is increased. Therefore, the boiling point becomes high.

Thus, in this embodiment, the liquid boil-off gas transferred from the reliquefaction apparatus to the high pressure pump22is prevented from being again evaporated through control of adjusting whether to bypass the condenser32by using the temperature of the refrigerant as a variable, so that a cavitation phenomenon in the high pressure pump22can be prevented in advance.

In addition, as the internal pressure of the gas-liquid separator33is controlled to correspond to the pressure of the liquid liquefied gas collected in the liquefied gas collection line L30, only the liquid phase can be stably introduced into the introduction end of the high pressure pump22while the condenser32and the cooler41are operated by using the same refrigerant as described above.

As described above, when the temperature of the refrigerant used in the condenser32is a low temperature, the pressure of the liquid boil-off gas transferred from the reliquefaction apparatus to the high pressure pump22is low. Therefore, the liquid boil-off gas may be evaporated and then introduced into the high pressure pump22. Hence, in this embodiment, control of allowing a portion of the boil-off gas to bypass the condenser32according to the temperature of the refrigerant is applied, thereby effectively solve the above-described problem.

FIG.3is a conceptual view illustrating a gas treatment system in accordance with a third embodiment of the present invention.

Referring toFIG.3, in the gas treatment system1in accordance with the third embodiment of the present invention, as compared with the above-described second embodiment, the fuel tank12may be omitted, and the liquefied gas transfer line L21, the boil-off gas transfer line L12, or the like may also be omitted.

In this case, the liquefied gas supply line L20may be directly connected from the cargo tank10to the propulsion engine E, and the low pressure pump21, the high pressure pump22, the heat exchanger23, and the like may be provided on the liquefied gas supply line L20.

The low pressure pump21may be disposed downstream of the transfer pump11in the liquefied gas supply line L20as shown in the drawing. However, when a discharge pressure of the transfer pump11is provided to correspond to an introduction pressure of the high pressure pump22, the low pressure pump21may omitted.

In addition, in this embodiment, the reliquefaction apparatus may transfer liquefied boil-off gas to the liquefied gas supply line L20between the cargo tank10and the high pressure pump22. In the fuel supply mode, the reliquefaction apparatus may transfer a liquid phase separated in the gas-liquid separator33to the liquefied gas supply line L20upstream of the high pressure pump22such that the liquid phase is supplied to the propulsion engine E.

Also, like the above-described embodiment, the reliquefaction apparatus liquefies boil-off gas to be transferred to the high pressure pump. A portion of the boil-off gas may bypass the condenser32and be transferred to the liquefied gas supply line L20upstream of the high pressure pump22via the gas-liquid separator33according to the temperature of a refrigerant.

FIG.4is a conceptual view illustrating a gas treatment system in accordance with a fourth embodiment of the present invention.

Referring toFIG.4, in the gas treatment system1in accordance with the fourth embodiment of the present invention, as compared with the above-described second embodiment, the boil-off gas supply line L13is omitted, and a collection point of liquefied gas is set to the fuel tank12.

In this embodiment, the reliquefaction apparatus may transfer liquefied boil-off gas to the fuel tank12. This may be made by the boil-off gas transfer line L12as described above. That is, in the fuel supply mode, the reliquefaction apparatus may transfer a liquid phase separated in the gas-liquid separator33to the fuel tank12such that the liquid phase is supplied to the propulsion engine E.

However, in this embodiment, the liquefied gas collection line L30of the fuel collection part40may extend from the propulsion engine E to be connected to the inside the fuel tank12. Therefore, the liquefied gas collection line L30may transfer, to the fuel tank12, surplus liquid liquefied gas mixed with a lubricant used in the propulsion engine E. The liquid liquefied gas introduced into the fuel tank12may be reintroduced into the propulsion engine E through the low pressure pump21and the high pressure pump22.

The fuel tank12of this embodiment is a component which allows the surplus liquefied gas to be directly collected thereinside, and an internal pressure of the fuel tank12may be set high as compared with the above-described second embodiment. That is, the internal pressure of the fuel tank12may be adjusted as a pressure at which the collected liquefied gas is not evaporated. In this case, when the internal pressure of the fuel tank12corresponds to the introduction pressure of the high pressure pump22, the low pressure pump21may be omitted.

Like the second and third embodiments, in this embodiment, the flow of liquid boil-off gas may be controlled according to the temperature of a refrigerant used in the condenser32. Specifically, in this embodiment, the reliquefaction apparatus may allow at least a portion of the boil-off gas to be supplied to the fuel tank12while bypassing the condenser32so as to prepare for fluctuation of the pressure of boil-off gas transferred to the fuel tank12according to the temperature of the refrigerant.

In this embodiment, the liquid boil-off gas is transferred to the high pressure pump22via the fuel tank12, and the low pressure pump21may be provided between the fuel tank12and the high pressure pump21. Therefore, the temperature of the refrigerant of the condenser32has influence on the internal pressure of the fuel tank12. This may have influence on the introduction pressure of the low pressure pump21. This may have indirect influence on the introduction pressure of the high pressure pump. When the low pressure pump21is omitted, the internal pressure of the fuel tank12may have direct influence on the introduction pressure of the high pressure pump22.

Therefore, the reliquefaction apparatus of this embodiment may allow at least a portion of the boil-off gas to be supplied to the fuel tank12via the gas-liquid separator33while bypassing the condenser32so as to prepare for fluctuation of the pressure of boil-off gas transferred from the gas-liquid separator33to the fuel tank12according to the temperature of the refrigerant. That is, in this embodiment, the internal pressure of the gas-liquid separator33and the internal pressure of the fuel tank12may be simultaneously controlled through bypass adjustment of the boil-off gas.

Alternatively, in this embodiment, the liquid boil-off gas liquefied in the condenser32is transferred to the high pressure pump22via the fuel tank12, and therefore, the fuel tank12may implement a gas-liquid separation function. Hence, the gas-liquid separator33in the reliquefaction apparatus may be omitted.

FIG.5is a conceptual view illustrating a gas treatment system in accordance with a fifth embodiment of the present invention.

Referring toFIG.5, in the gas treatment system1in accordance with a fifth embodiment of the present invention, as compared with the second embodiment, a connection point of the boil-off gas supply line L13may be differently provided.

The boil-off gas supply line L13of this embodiment may transfer boil-off gas upstream of the gas-liquid separator33to the liquefied gas supply line L20between the fuel tank12and the high pressure pump22. That is, one end of the boil-off gas supply line L13may be connected between the condenser32and the gas-liquid separator33in the reliquefaction apparatus, and the other end of the boil-off gas supply line L13may be connected to an upper stream of the high pressure pump22in the liquefied gas supply line L20.

The boil-off gas supply line L13is provided to prepare for fluctuation of the internal pressure of the gas-liquid separator33according to the temperature of a refrigerant. Specifically, when the temperature of the refrigerant is a low temperature which is lower than a reference value, the boil-off gas supply line L13may allow an upper stream of the high pressure pump and an upper stream of the gas-liquid separator33to be directly connected to each other so as to prevent pressure from not being sufficient when the boil-off gas is overcooled in the condenser32to be introduced into the high pressure pump22via the gas-liquid separator33.

In this case, the compressor31of the reliquefaction apparatus is in a situation in which the condenser32and the high pressure pump22are sequentially disposed downstream of the compressor31according to flow of the boil-off gas, and therefore, a pressure of the introduction end of the high pressure pump22is matched to a pressure of the discharge end of the compressor31. Therefore, an operation of the compressor31may be controlled while receiving, as resistance, the introduction pressure of the high pressure pump22(pressure of liquid liquefied gas collected through the liquefied gas collection line L30), so that the discharge pressure of the compressor31is adjusted upwardly.

That is, in this embodiment, when the temperature of the refrigerant used in the condenser32is extremely low, the discharge end of the compressor31receives resistance due to the introduction pressure of the high pressure pump22by allowing a lower stream of the condenser32and an upper stream of the high pressure pump22to be directly connected to the boil-off gas supply line L13. Therefore, the discharge pressure of the compressor31is controlled to correspond to the introduction pressure of the high pressure pump22.

Thus, in this embodiment, instead of bypassing heat exchange with low-temperature refrigerant, a lower stream of the condenser32and an upper stream of the high pressure pump22are connected to each other while bypassing the gas-liquid separator33to have the same pressure, so that the discharge pressure of the compressor31corresponds to the introduction pressure of the high pressure pump22.

As described above, in this embodiment, the discharge pressure of the compressor31corresponds to the introduction pressure of the high pressure pump22by allowing a lower stream of the compressor3and an upper stream of the high pressure pump22to be connected to each other so as to prevent the pressure of the liquid boil-off gas from not be sufficient as the temperature of the refrigerant used in the condenser32is extremely low. Thus, evaporation in the high pressure pump22can be effectively prevented.

FIG.6is a conceptual view illustrating a gas treatment system in accordance with a sixth embodiment of the present invention.

Referring toFIG.6, in the gas treatment system1in accordance with a sixth embodiment of the present invention, as compared with the fifth embodiment, the fuel tank12may be omitted, and the liquefied gas transfer line L21, the boil-off gas transfer line L12, or the like may also be omitted.

In this case, the liquefied gas supply line L20may be directly connected from the cargo tank10to the propulsion engine E, and the low pressure pump21, the high pressure pump22, the heat exchanger23, and the like may be provided on the liquefied supply line L20. The low pressure pump21may be omitted, which has been described in the above-described third embodiment.

In this embodiment, the reliquefaction apparatus may transfer liquefied boil-off gas to the liquefied gas supply line L20between the cargo tank10and the high pressure pump22. In the fuel supply mode, the reliquefaction apparatus may transfer a liquid phase separated in the gas-liquid separator33to the liquefied gas supply line L20upstream of the high pressure pump22such that the liquid phase is supplied to the propulsion engine E.

Also, like the above-described embodiment, the reliquefaction apparatus liquefies boil-off gas and transfers the liquefied boil-off gas to the high pressure pump22. The reliquefaction apparatus allows a lower stream of the condenser32and an upper stream of the high pressure pump22to be connected to each other according to the temperature of a refrigerant, so that a discharge pressure of the compressor31corresponds to an introduction pressure of the high pressure pump22.

FIG.7is a conceptual view illustrating a gas treatment system in accordance with a seventh embodiment of the present invention.

Referring toFIG.7, in the gas treatment system1in accordance with the seventh embodiment of the present invention, as compared with the above-described embodiment, a detailed configuration of the reliquefaction apparatus is changed, and the other components may include components of at least one of the above-described embodiments.

The reliquefaction apparatus of this embodiment includes the compressor31, the condenser32, the gas-liquid separator33, the aftercooler35, and a boil-off gas heat exchanger37. The compressor31, the condenser32, and the gas-liquid separator33have been described above, and therefore, their detailed descriptions will be omitted.

The boil-off gas heat exchanger37heat-exchanges boil-off gas transferred from the cargo tank10to the compressor31with boil-off gas liquefied in the condenser32. Specifically, the boil-off gas heat exchanger37may be provided in 2-stream structure having a stream along which the boil-off gas transferred from the cargo tank10to the compressor31flows and a stream along which boil-off gas transferred from the gas-liquid separator33to the cargo tank10flows.

In an example, the boil-off gas heat exchanger37may be provided on the boil-off gas return line L11to have one stream parallel to the boil-off gas discharge line L10and another stream parallel to the boil-off gas return line L11. The boil-off gas heat exchanger37may be provided to substitute for the above-described intercooler34. It will be apparent that the boil-off gas heat exchanger37may be added to the above-described embodiment having the intercooler34.

Since the boil-off gas liquefied in the condenser32is in a state in which the liquefied boil-off gas is compressed in the compressor31, the temperature of the boil-off gas may be higher than a boiling point at atmospheric pressure even though the boil-off gas is in a liquid phase. On the other hand, boil-off gas discharged from the cargo tank10may have a temperature close to the boiling point while having a pressure at an atmospheric pressure level.

Therefore, the heat exchanger37may cool the boil-off gas transferred from the gas-liquid separator33by heat-exchanging the boil-off gas transferred from the gas-liquid separator33with low-temperature boil-off gas discharged from the cargo tank10. Boil-off gas as a cooling object in the boil-off gas heat exchanger37and boil-off gas as a cooling subject in the boil-off gas heat exchanger37may have different pressures. A pressure difference may be formed as a pressure difference between an internal pressure in the cargo tank10and an internal pressure of the gas-liquid separator33.

A decompression valve (not shown) may be provided at at least one point in an upper or lower stream of the boil-off gas heat exchanger37on the boil-off gas return line L11, so that additional cooling is implemented by decompressing the boil-off gas compressed in the compressor31.

The reliquefaction apparatus including the boil-off gas heat exchanger37may be operated in the fuel supply mode or the reliquefaction mode as described in the above-described first embodiment. That is, the reliquefaction apparatus may be operated in the reliquefaction mode in which the liquid phase separated in the gas-liquid separator33is transferred to the cargo tank10via the boil-off gas heat exchanger37provided on the boil-off gas return line L11, and/or be operated in the fuel supply mode in which the liquid phase separated in the gas-liquid separator33is transferred to the fuel tank12through the boil-off gas transfer line L12to be supplied to the propulsion engine E.

As described above, in this embodiment, the boil-off gas heat exchanger37is used instead of the intercooler34, so that the structure of the reliquefaction apparatus can be simplified. In addition, boil-off gas circulation through the intercooler34is omitted, so that the reliquefaction volume of the reliquefaction apparatus can be increased.

It will be apparent that, in addition to the embodiments described above, the present invention may include, as additional embodiment, a combination of at least one of the embodiments and prior art and a combination of at least two of the embodiments.

Although the present invention has been described with reference to exemplary embodiments illustrated in the drawings for illustrative purposes, this is for the purpose of describing and not limiting the invention. Various modifications, which will become apparent to those skilled in the art, are within the scope of this invention described in the attached claims.

All simple modifications or changes of the present invention belong to the scope of the present invention, and the specific protection scope of the present invention will be made clear by the appended claims.