KR20200048094A - Boil-Off Gas Treatment System And Method For Ship - Google Patents

Abstract

Disclosed are a boil-off gas treatment system for a vessel and a method thereof. According to an embodiment of the present invention, the boil-off gas treatment system for a vessel includes: a compressor receiving and compressing boil-off gas (BOG) produced from an LNG storage tank of a vessel; a re-condenser receiving the compressed BOG from the compressor and mixing the BOG with LNG supplied from the LNG supply tank to condense the LNG; a regasification gas transfer part receiving the condensed LNG from the re-condenser to transfer the LNG to the outside of the vessel by compressing and gasifying the LNG; and a boosting compressor receiving the compressed BOG from the compressor to additionally compress the BOG with compression pressure from the regasification gas transfer part. When the amount of the BOG produced from the LNG storage tank is large or the send-out rate of the regasification gas through the re-condenser and the regasification gas transfer part is low, the additionally compressed BOG from the boosting compressor can be transferred to the outside of the vessel. Therefore, the boil-off gas treatment system is capable of lowering costs for maintenance by using a main engine for propulsion and power production.

Description

Boil-off gas treatment system and method for ship

The present invention relates to an evaporation gas treatment system and method for a ship, and more specifically, receives compressed BOG from a compressor in addition to a compressor that receives and compresses BOG (Boil Off Gas) generated in the LNG storage tank of the ship. A boosting compressor that is further compressed by the compression pressure at the regasification gas transfer section is prepared, and the BOG generated from the LNG storage tank is used as fuel to produce propulsion and electric power, and the amount of BOG is high or the recondenser and regasification gas transfer section The present invention relates to a system and method for treating boil-off gas in a vessel that enables the additional compressed BOG to be transported out of the vessel when the re-gas return rate is low.

Natural gas is a fossil fuel that contains methane as a main component and contains a small amount of ethane and propane, and has recently been spotlighted as a low-pollution energy source in various technical fields.

Natural gas is consumed a lot with economical and eco-friendly energy, but it has a large volume and is inefficient in transportation and storage to transport it as a natural gas.

In order to compensate for this, a method of transporting and storing in a liquefied natural gas (LNG) state has been proposed. Liquefied natural gas is a colorless, transparent, cryogenic liquid whose natural gas, mainly composed of methane, is cooled at atmospheric pressure to a cryogenic condition of -162 ° C, reducing its volume to 1/600.

However, since the natural gas liquefaction temperature is extremely low at -162 ° C under normal pressure, LNG is easily sensitive to temperature changes and evaporates easily. Although the LNG storage tank of the LNG carrier is insulated, since external heat is continuously transferred to the LNG storage tank, LNG is continuously vaporized in the LNG storage tank during the LNG transportation process by the LNG carrier, and LNG Boil-off gas (BOG) is generated in the storage tank.

BOG is a kind of LNG loss, which is an important problem in the transportation efficiency of LNG, and when boil-off gas accumulates in the LNG storage tank, the pressure in the LNG storage tank rises excessively, and there is a risk of damage to the tank. A variety of methods for dealing with are being studied.

Recently, for the treatment of BOG, a method of re-liquefying BOG and returning it to a storage tank, a method of using BOG as an energy source of a ship engine, and the like are used. And for the excess BOG, a method of combustion in a gas combustion unit (GCU) is used.

In addition, a dual fuel engine has been developed that can use natural or forced vaporized gas and fuel oil as fuel in propulsion or power generation devices in the LNG carrier itself, and is used as the main engine and generator engine. It is also supplied as fuel on board.

1 schematically shows a vessel provided with an engine that receives fuel from a conventional LNG storage tank.

As shown in FIG. 1, a plurality of engines are provided on a ship, and when a regasification plant is driven in a FSRU (Floating Storage Regasification Unit), a plurality of large engines are provided because power consumption is high. When a 4-stroke Dual Fuel engine is provided, LNG or BOG is supplied from the LNG storage tank (T) to the engine (E) via the fuel supply unit (10), and oil such as HFO, MDO, LSMGO is also supplied.

Electricity produced by driving the engine E passes through a switchboard (SWBD), a propeller through a transformer 20, a converter 30, a propulsion motor 40, a reduction gear 50, for example, a fixed pitch It is transmitted as power to the propeller (FPP).

These 4-Stroke engines provided in the FSRU can be less efficient than 2-Stroke engines, and the engine output is transmitted to the propellers through the switchboard, transformer, converter, propulsion motor, and reduction gear, so the output is lost through each stage. This can occur, and there is a problem of high maintenance costs.

 In addition, since the gas consumption on the onshore side is low and the regasification gas transfer rate is low or if the gas is not regasified for a long time, a lot of evaporation gas is generated in the storage tank. In order to maintain the tank pressure at an appropriate level, evaporation gas must be treated And, for this, there is a problem in that the evaporation gas cannot be efficiently used when it is burned and removed from the GCU (Gas Combustion Unit). In addition, since the GCU also consumes a large amount of power, there is a problem of double energy loss.

The present invention is intended to solve this problem, and to increase the flexibility of evaporation gas management, so as to more effectively manage evaporation gas, and to propose a system of a ship that can increase engine efficiency and reduce maintenance costs.

According to an aspect of the present invention for solving the above problems, a compressor that receives and compresses BOG (Boil Off Gas) generated in the LNG storage tank of the ship;

A re-condenser that receives compressed BOG from the compressor and mixes it with LNG supplied from the LNG storage tank;

A regasification gas transfer unit receiving the LNG condensed from the recondenser and compressing and vaporizing it to transport it to the outboard; And

It includes; a boosting compressor that receives compressed BOG from the compressor and further compresses it with the compression pressure in the regasification gas transfer unit.

When the amount of BOG generated in the LNG storage tank is large or the regasification gas send out rate through the recondenser and regasification gas transfer unit is low, additional compressed BOG from the boosting compressor can be transported to the outboard. It characterized in that the vessel is provided with a system for treating boil-off gas.

Preferably, the regasification gas transfer unit is supplied with LNG condensed from the re-condenser, the HP pump compressing at high pressure; An HP carburetor receiving and vaporizing compressed LNG from the HP pump; And a measurement unit that transfers gas vaporized from the HP vaporizer to the outside of the ship.

Preferably, further comprising a pressure reducer for receiving the gas vaporized from the downstream of the HP vaporizer and depressurizing and cooling it to supply it to the LNG storage tank, the BOG further compressed from the boosting compressor passes through the pressure reducer to the LNG storage tank Can be supplied with.

Preferably, the HP carburetor can vaporize the LNG by heat exchange with seawater by an open loop or a closed loop.

Preferably, the main engine that receives the compressed BOG from the compressor and produces the propulsion and electric power required for the ship; An axial generator connected to an axial system including an axis that delivers the output of the main engine to the propeller of the ship to produce power with the output of the main engine; A clutch separating the main engine and the shaft generator from the propeller and shaft; And a generator engine that receives the compressed BOG from the compressor and produces the electric power required for the ship.

Preferably, the main engine is a 2-stroke engine supplied with BOG compressed to 8 to 15 bar, the generator engine is a 4-stroke engine, and the main engine and the shaft generator are used even when the ship is not in propulsion. Can produce electricity.

According to another aspect of the present invention, the BOG (Boil Off Gas) generated in the LNG storage tank of the vessel is compressed with a compressor, the compressed BOG is supplied to a re-condenser, mixed with LNG supplied from the LNG storage tank, and condensed. Compressed and vaporized and transported to the ship,

When the amount of BOG generated in the LNG storage tank is large or the regasification gas send out rate through the recondenser is low, the compressed BOG is further compressed with a boosting compressor to compress the additional compressed BOG. Provided is a method for treating boil-off gas in a ship, which is capable of being transported out of the ship.

Preferably, the BOG compressed by the compressor is supplied to the main engine and generator engine of the ship to produce the propulsion and electric power required for the ship, but an axial generator capable of producing electric power with the output of the main engine is the main engine. Is connected to the shaft system including the shaft for transmitting the output of the propeller, and the main engine and the shaft generator and a clutch for separating the propeller and the shaft is provided, it is possible to produce electric power with the main engine and shaft generator even when the ship is not in propulsion have.

 In the present invention, when the amount of BOG generated in the LNG storage tank is high, or when the regasification gas send out rate through the recondenser and regasification gas transfer unit is low, the BOG can be re-liquefied or regasified By allowing the gas to be transferred directly from the boosting compressor, which has a better turn down than the gas transfer section, to the onshore, the BOG can be managed more effectively and the flexibility in system operation can be increased.

By applying the 2-stroke engine as the main engine, it is possible to increase efficiency, lower operating costs, and adopt a shaft generator to reduce equipment failure and reduce maintenance costs.

1 schematically shows a vessel provided with an engine that receives fuel from a conventional LNG storage tank.
2 schematically shows a system for treating boil-off gas in a ship according to an embodiment of the present invention.

In order to fully understand the operational advantages of the present invention and the objects achieved by the practice of the present invention, reference should be made to the accompanying drawings and the contents described in the accompanying drawings, which illustrate preferred embodiments of the present invention.

Hereinafter, the configuration and operation of the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. Here, when adding reference numerals to the components of each drawing, it should be noted that the same components are denoted by the same reference numerals as much as possible even though they are displayed on different drawings.

In the embodiments of the present invention described below, the vessel may be an engine that can use liquefied gas as fuel for a propulsion engine or fuel for a power generation engine, or may be any type of vessel that uses liquefied gas as fuel. Typically, self-propelled ships such as LPG carriers, LNG carriers, liquid hydrogen carriers, and LNG regasification vessels (LVs), LNG floating production storage offloading (FPSO), and LNG floating storage regasification units (FSRUs) As well, offshore structures floating on the sea are included.

In addition, the present embodiments can be applied to a fuel supply system of all types of liquefied gas that can be transported by liquefying at a low temperature, generating evaporation gas in a stored state, and supplying fuel to the engine. Such liquefied gas is, for example, liquefied petrochemicals such as Liquefied Natural Gas (LNG), Liquefied Ethane Gas (LEG), Liquefied Petroleum Gas (LPG), Liquefied Ethylene Gas, Liquefied Propylene Gas, etc. It can be gas.

In embodiments to be described later, an LNG floating vessel regasification unit (FSRU) among ships to which LNG, which is one of typical liquefied gases, is applied, will be described as an example.

2 schematically shows a system for treating boil-off gas in a ship according to an embodiment of the present invention.

As shown in FIG. 2, the boil-off gas treatment system of this embodiment receives the BOG (Boil Off Gas) generated in the LNG storage tank of the ship and compresses the compressed air (100a, 100b), and receives the compressed BOG from the compressor. Recondenser 200 to condense by mixing with LNG supplied from the LNG storage tank, regasification gas transfer unit 300 that receives compressed and vaporized LNG from the recondenser and transports it to the outside of the vessel, and supplies compressed BOG from the compressor And a boosting compressor 400 that receives and further compresses the compressed gas at the regasification gas transfer unit.

The ship in this embodiment transfers the regasification gas from the LNG storage tank to the outboard as the FSRU, but the amount of BOG generated in the LNG storage tank is large or the regasification gas transfer rate through the recondenser and the regasification gas transfer unit (send When the out rate) is low, it is characterized in that the additional compressed BOG from the boosting compressor 400 can be transferred to the outboard.

The main engine (ME) that receives the compressed BOG from the compressors (100a, 100b) to produce the propulsion and electric power required for the ship and the compressed BOG from the compressor to produce the electric power required for the ship in the ship of this embodiment. The generator engine GE is provided, and the propeller PP generating the propulsion of the ship using the output of the main engine is connected to the shaft S that transmits the output of the main engine to the propeller PP, and includes such a shaft. The shaft generator SG is connected to the shaft system. In addition, a clutch (C) is provided to separate the main engine and the shaft generator from the propeller and shaft. The main engine is a 2-stroke engine supplied with BOG compressed at the pressure required by the engine, and the generator engine can be configured as a 4-stroke engine. The main engine is a 2-stroke engine supplied with compressed gas at 8 to 15 bar, more preferably 10 to 13 bar, and may be, for example, an X-DF engine of WinGD (Company).

By applying the 2-stroke engine as the main engine in this way, it is possible to increase the efficiency during sailing, and by using the shaft generator, the power required during sailing can be produced as the output of the main engine, and the shaft generator and the main engine are separated from the shaft. By adopting the clutch, even when not in the voyage, for example, during regasification transfer, the main engine ME and the shaft generator SG can be used to produce the required power.

This saves fuel costs both on and off the sea, and reduces the frequency of equipment failures and maintenance costs. In addition, the frequency of use of the generator engine GE can be reduced, and the number of units can be reduced.

On the other hand, the regasification gas transfer unit 300 receives the condensed LNG from the re-condenser 200, and compresses the HP pump 310 at high pressure, and the HP vaporizer 320 that vaporizes the compressed LNG from the HP pump, HP It includes a metering unit (330), a heat exchanger (340), a manifold (350), etc. to transfer the gas vaporized from the vaporizer to the outside of the ship.

When the pressure at the rear end of the compressor is raised to 10 to 13 bar required for the main engine, the pressure of the BOG supplied to the recondenser also increases, which may lead to an increase in the efficiency of the recondenser.

The HP carburetor 320 can vaporize LNG by heat exchange with seawater by an open loop or a closed loop, and the system of FIG. 2 includes seawater with a heat medium such as glycol water. A closed loop system is shown in which heat exchange, heat medium circulates through the closed loop and reheats LNG by transferring heat energy from seawater through heat exchange with LNG in an HP vaporizer. Instead, it can also be configured as a system that directly transfers the heat energy of seawater to LNG through an open loop to regasify it.

The system further includes a pressure reducer 500 that receives the vaporized gas from the downstream of the HP vaporizer and decompresses and cools it and supplies it to the LNG storage tank T, but the BOG additionally compressed from the boosting compressor 400 decompresses It can be supplied to the LNG storage tank (T) via the group (500).

The pressure reducer may be, for example, a J-T valve that cools the compressed gas with adiabatic expansion.

In this way, the system of the present embodiment is configured when the amount of BOG generated in the LNG storage tank is high, or when the regasification gas send out rate through the recondenser and regasification gas transfer unit is low, by configuring the boosting compressor and the pressure reducer. BOG can be managed more effectively by allowing the BOG to be re-liquefied through the boosting compressor and JT valve, or by transferring the gas directly from the boosting compressor, which has a better turn down than the regasification gas transfer unit, to the onshore. Can increase the flexibility.

The present invention is not limited to the above embodiments, and can be variously modified or modified within a range not departing from the technical gist of the present invention, which is obvious to those skilled in the art to which the present invention pertains. Did.

T: LNG storage tank
ME: main engine
PP: propeller
S: axis
C: Clutch
SG: axial generator
GE: Generator engine
100a, 100b: compressor
200: recondenser
300: regasification gas transfer unit
310: HP pump
320: HP Carburetor
330: measurement unit
340: heat exchanger
350: Manifold
360: sea water heat exchanger
GL: glycol water circulation line
400: boosting compressor
500: pressure reducer
FP, CP: Pump
LC: LNGC
600: HD compressor

Claims (8)

A compressor that receives and compresses BOG (Boil Off Gas) generated in a LNG storage tank of a ship;
A re-condenser that receives compressed BOG from the compressor and mixes it with LNG supplied from the LNG storage tank;
A regasification gas transfer unit receiving the LNG condensed from the recondenser, compressing and vaporizing it, and transferring it to the outboard; And
It includes; a boosting compressor receiving the compressed BOG from the compressor and further compressing it with the compression pressure in the regasification gas transfer unit;
When the amount of BOG generated in the LNG storage tank is large or the regasification gas send out rate through the recondenser and the regasification gas transfer unit is low, additional compressed BOG from the boosting compressor can be transported to the outboard. Vessel evaporation gas treatment system characterized in that there is. According to claim 1, Regasification gas transfer unit
An HP pump that receives LNG condensed from the re-condenser and compresses it at high pressure;
An HP carburetor receiving and vaporizing compressed LNG from the HP pump; And
The evaporation gas treatment system of the ship comprising; a measurement unit for transferring the gas vaporized in the HP vaporizer to the outside of the ship. According to claim 2,
Further comprising a pressure reducer for receiving the gas vaporized from the downstream of the HP vaporizer and cooling and reducing the pressure to supply to the LNG storage tank,
BOG compressed from the boosting compressor can be supplied to the LNG storage tank through the pressure reducer, characterized in that the ship's evaporation gas treatment system. According to claim 2,
The HP vaporizer is an open loop (close loop) or closed loop (closed loop) of the ship's evaporation gas treatment system, characterized in that to vaporize the LNG by heat exchange with seawater. According to claim 1,
A main engine that receives compressed BOG from the compressor and produces propulsion and electric power required for the ship;
An axial generator connected to an axial system including an axis that delivers the output of the main engine to the propeller of the ship to produce power with the output of the main engine;
A clutch separating the main engine and the shaft generator from the propeller and shaft; And
And a generator engine that receives the compressed BOG from the compressor and produces the electric power required for the ship. The method of claim 5,
The main engine is a 2-stroke engine supplied with BOG compressed to 8 to 15 bar,
The generator engine is a 4-stroke engine,
The ship's evaporation gas treatment system, characterized in that power can be produced by the main engine and the shaft generator even when the ship is not in propulsion. BOG (Boil Off Gas) generated in the LNG storage tank of the ship is compressed with a compressor, and compressed BOG is supplied to a re-condenser, mixed with LNG supplied from the LNG storage tank, condensed, compressed and vaporized, and transported to the outboard. Ha,
When the amount of BOG generated in the LNG storage tank is large or the regasification gas send out rate through the recondenser is low, the compressed BOG is further compressed with a boosting compressor to compress the additional compressed BOG. Method for treating the boil-off gas of a ship, characterized in that it can be transferred to the outboard. The method of claim 7,
Supplying the BOG compressed by the compressor to the ship's main engine and generator engine to produce the propulsion and power required for the ship,
A shaft generator capable of producing electric power with the output of the main engine is connected to a shaft system including a shaft that delivers the output of the main engine to a propeller, and a clutch for separating the main engine and shaft generator from the propeller and shaft is provided. A method for treating boil-off gas in a ship, characterized in that electric power can be produced by the main engine and the shaft generator even when the ship is not in propulsion.

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