KR20150057780A - System and method for management of Boil-Off Gas - Google Patents

Abstract

The present invention relates to a boil-off gas (BOG) treatment system and method. More specifically, the present invention relates to the boil-off gas treatments system which efficiently recovers boil-off gas, reduces installation costs, facilitates a pressure control inside a cargo tank and cools boil-off gas using LNG which is to be evaporated, and at the same time uses the boil-off gas heat in evaporating the LNG for a more efficient treatment of boil-off gas. According to the present invention, the boil-off gas treatment system comprises: a suction drum installed on board to temporarily store LNG supplied from the cargo tank wherein LNG is stored; an LNG pump to pump LNG supplied from the suction drum; a heat exchanger to exchange heat between the LNG transported by the LNG pump and the boil-off gas from the cargo tank; and a compressor to compress boil-off gas supplied to the heat exchanger. Boil-off gas cooled in the heat exchanger is recovered into the cargo tank and mixed with LNG on the center part of the cargo tank for liquefaction.

Description

[0001] BOG processing system and method [0002]

The present invention relates to a BOG processing system and method, and more particularly, to a BOG processing system and method configured to efficiently retrieve BOG.

In general, natural gas is transported in the form of gas through land or sea gas pipelines, or transported to a remote location where it is stored in an LNG carrier in the form of Liquefied Natural Gas (LNG). LNG is obtained by cooling natural gas at a cryogenic temperature (approximately -163 ° C), and its volume is reduced to approximately 1/600 of that of natural gas, making it well suited for long distance transport through the sea.

The LNG-RV (LNG-Regasification Vessel), which is used to transport LNG, transports LNG to the sea, arrives at the land area, reloads the stored LNG and unloads it in natural gas. To this end, pump, and high-pressure vaporizer (HP Vaporizer). In the regeneration process, BOG (Boil-Off Gas, hereinafter referred to as "BOG") is generated due to heat intrusion. The internal pressure of the cargo tank increases due to the generation of BOG, However, it becomes difficult to manage natural gas efficiently. Therefore, a device for processing BOG is needed to solve this problem.

As a conventional BOG processing apparatus, there is an evaporation gas processing apparatus and method for reducing the re-liquefying power consumption amount of Korean Patent Laid-Open No. 10-2011-0118988. A liquefaction device for re-liquefying the evaporation gas generated in the storage tank and returning the evaporation gas to the storage tank; and an evaporator for supplying the evaporation gas supplied from the storage tank to the re-liquefier, And a heat exchanger for cooling by heat exchange with the liquefied gas from the tank. And the evaporated gas cooled while passing through the heat exchanger is supplied from the storage tank to the recondenser through a branch line branching from a first supply line for supplying an evaporative gas to the re-liquefier, the evaporated gas supplied to the recondenser Is re-condensed by receiving the cold heat of the liquefied gas from the storage tank.

However, in the conventional BOG treatment apparatus, the use of the recondenser requires a lot of cost for the installation of the recondenser, thereby causing a problem of high cost of the BOG treatment.

SUMMARY OF THE INVENTION The present invention has been made to solve the conventional problems as described above, and it is an object of the present invention to efficiently recover BOG, reduce installation cost, and facilitate pressure control inside a cargo tank.

According to an aspect of the present invention, there is provided a suction drum, comprising: a suction drum installed in a ship and temporarily storing LNG supplied from a cargo tank storing LNG;

An LNG pump for pumping LNG supplied from the suction drum;

A heat exchanger for exchanging heat between the LNG transported by the LNG pump and the BOG supplied from the cargo tank; And

And a compressor for compressing the BOG to be supplied to the heat exchanger,

The BOG cooled in the heat exchanger is recovered in the cargo tank and mixed with the LNG in the center of the cargo tank to be liquefied.

Preferably, the compressor is a low duty compressor, and the BOG can be compressed to a pressure of 1.5 to 2.5 bara.

The system may further include a recovery line extending to the center of the cargo tank so that the BOG cooled in the heat exchanger is recovered to the center of the cargo tank.

Preferably, the apparatus further includes a vaporizer installed at a rear end of the heat exchanger to vaporize the LNG passed through the heat exchanger.

Preferably, the suction drum, the LNG pump, and the heat exchanger may be installed in a supply line for regenerating LNG from an LNG-RV (LNG-Regasification Vessel) equipped with the cargo tank and unloading the LNG in a natural gas state have.

According to another aspect of the present invention, there is provided a method of manufacturing a cargo tank, comprising the steps of: 1) discharging BOG generated in a cargo tank to the outside and compressing the BOG;

2) heat-exchanging the compressed BOG with the LNG; And

3) introducing BOG cooled by heat exchange into the center of the cargo tank and liquefying it by mixing with LNG in the cargo tank.

Preferably, the BOG generated in the cargo tank is discharged to the outside, compressed to a pressure of 1.5 to 2.5 bara, and then heat-exchanged with the LNG.

According to the present invention, it is possible to efficiently recover the BOG, reduce the cost required for the installation, make it economical and easy to control the pressure inside the cargo tank, utilize the LNG to vaporize the BOG, By utilizing the heat of BOG to vaporize LNG, it is possible to construct an efficient system.

Brief Description of the Drawings Fig. 1 is a block diagram showing a BOG processing system according to an embodiment of the present invention; Fig.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, the following examples can be modified in various forms, and the scope of the present invention is not limited to the following examples.

1 is a block diagram showing a BOG processing system according to an embodiment of the present invention.

The BOG treatment system 100 according to an embodiment of the present invention includes a heat exchanger 130 for exchanging heat between the LNG and the BOG supplied from the cargo tank 10 and the BOG cooled by the heat exchanger 130 And recovered in the cargo tank 10 to be liquefied. The BOG treatment system 100 according to an embodiment of the present invention includes a suction drum 110 and an LNG pump 120 for supplying LNG from the cargo tank 10 to the heat exchanger 130, And a compressor 140 for compressing the input signal.

The BOG processing system 100 according to an embodiment of the present invention can be installed in, for example, an LNG-RV (LNG-Regasification Vessel) Or an offshore structure.

The suction drum 110 temporarily stores the LNG supplied from the cargo tank 10 and supplies the LNG to the LNG pump 120 by its internal pressure.

In the suction drum 110, the BOG generated in the LNG through the gas-liquid separation of the LNG is transferred to the BOG treatment apparatus (not shown) including the suction drum 110 or the re-liquefying apparatus, and only the LNG, Of LNG pump < RTI ID = 0.0 > 120 < / RTI >

The LNG pump 120 boosts the LNG supplied from the suction drum 110 to a high pressure and pumps it. For this purpose, a high-pressure pump (HP pump) may be used.

The heat exchanger 130 exchanges heat between the LNG transferred by the LNG pump 120 and the BOG supplied from the cargo tank 10. In this case, in the heat exchanger 130, BOG of about -130 ° C. and LNG of about -162 ° C. are exchanged with each other so that heat of BOG is used for vaporizing LNG and low temperature of LNG is used for cooling of BOG.

The suction drum 110, the LNG pump 120 and the heat exchanger 130 are connected to a supply line LNG-RV (LNG-Regasification Vessel) provided with a cargo tank 10 for re- (Not shown). Therefore, it is possible to use the heat of BOG when LNG is regasified for unloading in LNG-RV.

A vaporizer 160 may be installed downstream of the heat exchanger 130 in the supply line 150. The vaporizer 160 can be a high-pressure vaporizer, for example, in consideration of the fact that the gasification target is LNG. By vaporizing the LNG that is primarily heated by the heat exchange with the BOG by being installed at the rear end of the heat exchanger 130 The vaporization efficiency can be increased.

The compressor 140 is installed at the front end of the heat exchanger 130 to compress the BOG supplied to the heat exchanger 130. A low duty compressor having relatively low installation and maintenance costs can be used.

A recovery line 170 may be provided to provide a recovery path for the vapor from the cargo tank 10. The recovery line 170 can provide a path for the BOG from the cargo tank 10 to be cooled, for example, through the compressor 140 and the heat exchanger 130 to be recovered to the cargo tank 10 as in the present embodiment. On the other hand, when the compressor 140 is composed of an LD compressor, the LD compressor is boosted to a certain pressure, for example, 1.5 to 2.5 bara, preferably 1.96 bara, It is difficult to supply LOGG to the lower portion of the cargo tank 10 and to liquefy by mixing with LNG, and it is necessary to liquefy BOG by mixing with LNG in the middle portion of the cargo tank 10. The recovery line 170 may be installed so that one end thereof extends to the center of the cargo tank 10 in order to recover the BOG cooled by the heat exchanger 130 to the center of the cargo tank 10. [

The operation of the BOG processing system according to the present invention will now be described.

The BOG generated from the cargo tank 10 is compressed by the compressor 140 through the recovery line 170 and supplied to the heat exchanger 130. The LNG stored in the suction drum 110 by the unloading pump 11 of the cargo tank 10 is supplied from the suction drum 110 to the heat exchanger 130 by pumping the LNG pump 120 to the heat exchanger 130 ) To allow heat exchange between LNG and BOG.

The BOG cooled by the heat exchange with the LNG in the heat exchanger 130 is recovered to the cargo tank 10 through the recovery line 170. The BOG is supplied to the center of the cargo tank 10 by the recovery line 170 And liquefied by mixing with LNG.

The LNG whose temperature has risen by heat exchange with the BOG in the heat exchanger 130 is vaporized while passing through the vaporizer 160 and is transported through the supply line 150.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. In addition to utilizing LNG, it is possible to construct an efficient system by utilizing the heat of BOG to vaporize LNG.

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

10: cargo tank 11: unloading pump
110: Suction drum 120: LNG pump
130: Heat exchanger 140: Compressor
150: supply line 160: vaporizer
170: recovery line

Claims (7)

A suction drum provided in the ship and temporarily storing LNG supplied from a cargo tank storing the LNG;
An LNG pump for pumping LNG supplied from the suction drum;
A heat exchanger for exchanging heat between the LNG transported by the LNG pump and the BOG supplied from the cargo tank; And
And a compressor for compressing the BOG to be supplied to the heat exchanger,
Wherein the BOG cooled in the heat exchanger is recovered in the cargo tank and mixed with the LNG in the center of the cargo tank to be liquefied. The method according to claim 1,
Wherein the compressor is a low duty compressor and compresses the BOG to a pressure of 1.5 to 2.5 bara. 3. The method of claim 2,
Further comprising a recovery line extending to a center of the cargo tank so that the BOG cooled in the heat exchanger is recovered to the center of the cargo tank. The method according to claim 1,
And a vaporizer installed at a rear end of the heat exchanger to vaporize the LNG passed through the heat exchanger. 5. The method according to any one of claims 1 to 4,
The suction drum, the LNG pump, and the heat exchanger,
(LNG-Regasification Vessel) equipped with the cargo tank, and is installed in a supply line for recharging LNG and unloading the LNG in a natural gas state. 1) discharging the BOG generated in the cargo tank to the outside and compressing the BOG;
2) heat-exchanging the compressed BOG with the LNG; And
3) introducing BOG cooled by heat exchange into the center of the cargo tank and liquefying it with LNG in the cargo tank. The method according to claim 6,
Wherein the BOG generated in the cargo tank is discharged to the outside, compressed at a pressure of 1.5 to 2.5 bara, and then heat-exchanged with the LNG.

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