KR20170011239A - BOG Treatment System - Google Patents

Abstract

The present invention discloses a system for treating evaporated gas. According to the present invention, the system for treating evaporated gas comprises: a multi-stage compressor having a compressor and an intermediate cooler alternating with each other and being provided with, and compressing boil off gas (BOG) generated from a storage tank of a ship where liquefied natural gas (LNG) is stored; re-liquefier liquefying the compressed BOG, compressed by the multi-stage compressor, by cooling the compressed BOG through heat exchange with uncompressed BOG to be provided from an upper area to the multi-stage compressor and reducing the pressure thereof using the multi-stage compressor; and an inline mixer installed in an upper area of the multi-stage compressor and the re-liquefier, being provided with the BOG generated from the storage tank, spraying LNG provided from the storage tank to cool the BOG, and providing the cooled BOG to the re-liquefier.

Description

[0001] BOG TREATMENT SYSTEM [0002]

The present invention relates to an evaporative gas treatment system, and more particularly, to an evaporative gas treatment system, which comprises a multi-stage compressor and a reflux unit, which is supplied with BOG generated from a storage tank and injects LNG supplied from a storage tank, The present invention relates to an evaporative gas processing system having an inline mixer provided upstream of a multi-stage compressor and a remanufacturing unit and having a uniform and highly efficient re-liquefaction performance.

Liquefied natural gas (hereinafter referred to as "LNG") is a colorless transparent liquid obtained by cooling methane-based natural gas to about -162 ° C. and liquefying it. / 600. ≪ / RTI > Therefore, it is very efficient to transport liquefied LNG when transporting natural gas. For example, an LNG carrier that can transport (transport) LNG is used.

Since the liquefaction temperature of natural gas is cryogenic at around -160 ℃ at normal pressure, LNG is sensitive to the temperature change and is easily evaporated even if the temperature slightly increases. LNG storage tanks of LNG carriers are heat-treated, but since external heat is continuously transferred to LNG storage tanks, LNG is constantly spontaneously vaporized in LNG storage tanks during LNG transportation by LNG carrier, Boil-off gas (BOG) is generated in the storage tank.

The amount of evaporative gas (BOG) generated in the storage vessel is about 0.05 vol% / day even when the vessel is equipped with a heat insulating structure. The conventional liquefied natural gas carrier carries 4 to 6 tons / It is known that about 300 tons of liquefied natural gas is vaporized and gasified in a single operation.

BOG is a kind of LNG loss, which is an important problem in the transport efficiency of LNG. When the evaporation gas accumulates in the LNG storage tank, the pressure in the LNG storage tank is excessively increased, Have been studied.

Recently, for the treatment of BOG, BOG is re-liquefied and returned to the storage tank, and BOG is used as energy source of engine of ship. In addition, the surplus BOG is combusted in a gas combustion unit (GCU).

The gas combustion unit burns surplus BOG inevitably for controlling the pressure of the storage tank when the BOG can not be utilized otherwise, resulting in a waste of the chemical energy possessed by the BOG by combustion.

When a dual fuel (DF) engine is applied as the main propulsion unit in the propulsion system of the LNG carriers, the evaporative gas generated in the LNG storage tank can be used as the fuel of the DF engine to process the evaporative gas, If the amount of evaporative gas generated in the LNG storage tank exceeds the amount of fuel used in the propulsion of the ship in the DF engine, the evaporation gas may be sent to a gas burner to incinerate it to protect the LNG storage tank.

In recent years, for the treatment of BOG, BOG is re-liquefied and returned to the storage tank, and BOG is used as an energy source for the fuel consuming place such as a ship engine.

The present applicant has proposed a re-liquefying apparatus which utilizes the cooling heat of the evaporation gas itself by using the evaporation gas as the cooling fluid on Jul. 10, 2013, No. 10-2013-0081029. The Partial Re-liquefaction System (PRS) proposed in the patent of No. 10-2013-0081029 is a device for re-liquefying the evaporated gas discharged outside the storage tank by using the evaporation gas itself as a refrigerant, It is possible to re-liquefy the evaporated gas without separately installing the re-liquefier, and it is evaluated as an epoch-making technology that can effectively reduce the overall natural evacuation rate (BOR) of the liquefied natural gas storage tank.

1 is a schematic configuration diagram of the redispersion apparatus of the present invention, No. 10-2013-0081029. Referring to FIG. 1, the process of re-liquefying the evaporation gas in the re-liquefier will be briefly described below.

The evaporated gas discharged from the storage tank 10 can be compressed through a multi-stage compressor including a plurality of compressors 30 and an intercooler (not shown). In the compressor shown in FIG. 1, five stages of compression and cooling are alternately performed while passing through five compressors 30, and are compressed. Some of the evaporated gas that has undergone the compression process is sent to a high-pressure fuel consuming station E1 requiring high-pressure fuel, for example, a high-pressure engine such as an ME-GI engine, Lt; / RTI > The evaporation gas (A line) supplied to the heat exchanger 20 through the multi-stage compression process is heat-exchanged in the heat exchanger 20 with the evaporation gas (B line) discharged from the storage tank 10 and introduced into the compressor. The temperature of the evaporation gas is increased through the compression process, so that the evaporation gas before compression discharged from the storage tank 10 is used as the refrigerant for cooling the compressed evaporation gas.

The evaporated gas (C line) cooled through heat exchange in the heat exchanger 20 after the compression is decompressed in the decompressor 40. At least a part of the evaporated gas compressed while passing through the heat exchanger (20) and the pressure reducing device (40) is re-liquefied. In the gas-liquid separator 50, the re-liquefied liquefied natural gas is separated from the evaporated gas remaining in the gaseous state, and the re-liquefied evaporated gas is returned to the storage tank 10, and the evaporated gas (D line) (B line) discharged from the storage tank 10 to the heat exchanger 20 again.

In the case where there is a low-pressure fuel consuming place which is supplied with a gas of lower pressure than the gas which has passed through all the multi-stage compressors in a ship, for example, three of the five compressors 30, And can be supplied as fuel to the fuel consumption destination E2. Further, when the amount of evaporative gas generated from the storage tank 10 is large and is supplied as fuel for the high-pressure and low-pressure fuel consuming destination and remains after liquefaction by the partial re-liquefier, venting or gas- ; Gas Combustion Unit) to incinerate.

The present applicant's prior art is a device capable of effectively treating the evaporation gas generated in the storage tank. However, as the evaporated gas generated in the storage tank flows directly into the heat exchanger 20 and the compressor 30, the temperature of the BOG changes There is a problem that the liquefaction performance is not uniform and changes.

In order to solve such a problem, the present invention proposes an evaporative gas processing system having a uniform re-liquefaction performance and high re-liquefaction efficiency.

According to an aspect of the present invention, there is provided a multi-stage compressor comprising: a compressor and an intercooler alternately provided to compress and supply BOG (Boil-off Gas) generated from a storage tank of a ship storing LNG;

A re-culling unit for cooling the compressed gas compressed in the multi-stage compressor by heat exchange with uncompressed BOG to be supplied from the upstream to the multi-stage compressor, and reducing the pressure to liquefy; And

And an inline mixer provided upstream of the multistage compressor and the re-culling unit for supplying BOG generated from the storage tank and injecting LNG supplied from the storage tank to cool the mixed LNG and supply the LNG to the re-culling unit do.

Preferably, the re-liquefier comprises a heat exchanger for cooling the compressed gas compressed in the multi-stage compressor by heat exchange with an uncompressed BOG to be supplied to the multi-stage compressor from the upstream to the multi-stage compressor, Liquid separator and a gas-liquid separator for separating the compressed gas supplied from the decompression device by the gas-liquid separator, wherein the BOG cooled by the in-line mixer passes through the gas-liquid separator and the heat exchanger, .

Preferably, the compressed gas compressed from the multi-stage compressor may be supplied to a high-pressure gas injection engine provided in the ship.

Preferably, the fuel cell system may further include a fuel supply unit for supplying the LNG from the storage tank, compressing and vaporizing the LNG, and supplying the LNG to the high-pressure gas injection engine.

Preferably, the fuel supply unit may include a high-pressure pump that receives LNG from the LNG storage tank and compresses the LNG from the high-pressure gas injection engine to a required fuel pressure of the high-pressure gas injection engine, and a carburetor that receives and supplies the compressed LNG from the high- have.

Preferably, the compressed gas compressed through a part of the multi-stage compressor may be supplied to a low-pressure gas injection engine provided in the ship.

Preferably, the fuel supply unit includes a decompressor provided downstream of the carburetor for reducing the pressure of the compressed and vaporized LNG to a fuel required pressure of the low-pressure gas injection engine, and a low-pressure gas injection engine Further comprising a heater for heating the low-pressure gas injection engine to a fuel-requiring temperature of the low-pressure gas injection engine, wherein the LNG passed through the pressure reducer and the heater can be supplied to the low-pressure gas injection engine.

According to another aspect of the present invention, there is provided a method of controlling a boil-off operation, comprising: a first stream for repeatedly compressing, intermediate cooling, and compressing BOG generated from an LNG stored in a storage tank of a ship; A second stream for compressing the BOG from the first stream by heat exchange with the uncompressed BOG to be supplied to the first stream from the storage tank and decompressing and liquefying the BOG; And a third stream for supplying LNG from the storage tank to the uncompressed BOG to be heat exchanged with the second stream for cooling.

Preferably, the fourth stream supplying the BOG compressed in the first stream to the high-pressure gas injection engine provided in the ship, and the BOG compressed through only a part of the first stream to the low-pressure gas injection engine provided in the ship And a fifth stream to be supplied.

Preferably, a sixth stream for pumping the LNG from the storage tank and for compressing and vaporizing the LNG and supplying it to the high pressure gas injection engine, and a second stream for decompressing and heating the compressed and vaporized LNG branched from the sixth stream, And a seventh stream supplied to the engine.

The evaporative gas processing system of the present invention is a system that can re-liquefy BOG generated from a storage tank by using evaporation gas and LNG itself, and thus does not require a separate refrigerant system, Can be reduced, and maintenance becomes convenient. Particularly, it is possible to keep the temperature of BOG constant by supplying LNG to BOG through cooling by injecting LNG through an inline mixer and then supplying it to the re-cure unit and multistage compressor, thereby maintaining remanent liquefaction performance uniformly, .

In addition, compressed evaporated gas can be supplied as fuel to the inboard engine, if necessary, so that the amount of natural gas wasted in the combustion of the GCU can be reduced, thereby improving the economic efficiency.

This efficient BOG treatment saves cost by securing the safety of storage tanks and vessels, increasing the transport efficiency of LNG, cooling the BOG compressed by BOG and LNG, and re-liquefaction without constructing a separate refrigerant system. And contribute to the securing of space on the ship.

Fig. 1 schematically shows a partial redistribution device capable of treating an evaporative gas according to the applicant's prior patent.
Figure 2 schematically depicts an evaporative gas treatment system according to one embodiment of the present invention.

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

Hereinafter, the present invention will be described in detail with reference to the preferred embodiments of the present invention with reference to the accompanying drawings. Like reference symbols in the drawings denote like elements.

First, the evaporation gas processing system described below of the present invention is a system for processing all kinds of ships and marine structures such as LNG carriers, Liquefied Ethane Gas (LEG) carriers, LNG RVs and LNG carriers equipped with storage tanks capable of storing low- It can be applied for evaporative gas treatment in marine structures such as LNG FPSO, LNG FSRU, including the same vessel.

In the following embodiments, LNG, which is a representative low-temperature liquid cargo, is described as an example for convenience of explanation, but the present invention is not limited thereto. Liquefied gas stored in such a storage tank may be any liquid cargo that can be transported by liquefaction at a low temperature. For example, in addition to LNG, LEG, LPG, liquefied nitrogen, liquefied gas such as ethylene, acetylene, propylene, and the like may be applicable. The present embodiment can be applied to the treatment of the evaporative gas generated from such liquefied gas.

FIG. 2 schematically shows an evaporative gas treatment system according to an embodiment of the present invention.

2, the system of the present embodiment includes compressors 110a, 110b, 110c, 110d and 110e and inter coolers 120a, 120b, 120c, 120d and 120e alternately arranged to store the LNG A multi-stage compressor 100 for receiving and compressing BOG (Boil Off Gas) generated from the tank T, and a multi-stage compressor 100 for compressing the compressed gas compressed by the multistage compressor into uncompressed BOGs to be supplied to the multi- And an inline mixer (200) for supplying BOG generated from the storage tank and cooling the LNG supplied from the storage tank, and cooling the LNG to the re-culling unit, mixer, 300) is provided upstream of the multistage compressor and the remanufacturing unit.

Since the temperature of the BOG generated in the storage tank T is lower than the temperature of the compressed gas compressed through the multi-stage compressor, the system of the present embodiment uses the BOG generated in the storage tank as the refrigerant for cooling the compressed gas in the re- However, when the amount of LNG stored in the storage tank is high, the temperature of the BOG is low. However, when the LNG is stored in the storage tank or when the amount of LNG stored in the tank is small, the temperature of the BOG may be relatively high have. When the temperature of the BOG generated in the storage tank increases, the BOG may not supply sufficient cold heat to the compressed gas. Also, as the temperature of the BOG introduced into the multistage compressor increases, the compression efficiency decreases and the BOG liquefaction performance deteriorates .

In order to solve such a problem, in this embodiment, an in-line mixer 300 is provided upstream of the remanufacturing unit 200 to inject LNG at about -160 DEG C supplied from the storage tank into the BOG to be introduced into the remanufacturing unit and multi- The refrigerant is cooled in the inline mixer, and then supplied to the re-cure unit, the temperature of the refrigerant BOG can be maintained at a constant low level in the re-cure unit, thereby enhancing the re-liquefaction efficiency and maintaining the re-liquefaction performance constant.

The supply of LNG from the storage tank to the inline mixer may be via the cooling line CL and the pump P for pumping from the storage tank may be a stripping pump pre- A cargo tank may be utilized or a separate pump may be provided.

The re-culling unit 200 includes a heat exchanger 210 for cooling the compressed gas compressed by the multistage compressor 100 by heat exchange with uncompressed BOG to be supplied from the multistage compressor to the multistage compressor from the upstream side, A decompression device 220 for decompressing the compressed gas by being supplied with the compressed gas, and a gas-liquid separator 230 for separating the decompressed compressed gas supplied from the decompression device.

The multistage compressor 100 includes compressors 110a, 110b, 110c, 110d and 110e for compressing BOG, that is, compression cylinders, and intermediate coolers 120a, 120b, 120c, 120d, 120e are alternately provided, and BOG is compressed at a pressure equal to or higher than the critical pressure so as to effectively re-liquefy the BOG. Since the critical pressure of methane, which makes up most of the BOG, is about 55 bara, the multistage compressor can compress the BOG to 70 bara or more, preferably about 100 bara or more. In FIG. 1, a multi-stage compressor including five compressors and five intermediate coolers is illustrated, but the number of compressors and intercoolers can be changed as needed.

When the BOG discharged from the storage tank T and compressed by the multistage compressor 100 is referred to as a first stream and the flow of the compressed gas cooled and decompressed from the downstream end to the multistage compressor and returned to the storage tank is referred to as a second stream , The second stream is cooled through heat exchange in a heat exchanger with a first stream of evaporated gas that is discharged from the storage tank and then fed to the multi-stage compressor.

After compression, the cooled BOG or the LNG condensed through cooling is supplied to decompression means 220 to be thermally expanded. The depressurization means may be, for example, a J-T valve or an expander, through which the BOG can be further cooled while being thermally expanded. The BOG or LNG, which is thermally expanded through the decompression means, is supplied to the gas-liquid separator 230 to be gas-liquid separated into vapor and liquid, and the liquid LNG is stored as a storage tank.

The BOG cooled by the LNG in the inline mixer 300 is also supplied to the gas-liquid separator 230 to remove condensate from the gas-liquid separator. Then, only the gas is supplied to the heat exchanger 210 as refrigerant, . The BOG having undergone heat exchange with the compressed gas is supplied to the multi-stage compressor 100 and compressed.

On the other hand, when an engine that consumes natural gas as fuel in the ship is provided, for example, a high-pressure gas injection engine, the compressed gas compressed from the multi-stage compressor 100 is supplied to the high-pressure gas injection engine E1 provided in the ship It is possible. Depending on the required amount of fuel required by the high-pressure gas injection engine, it may be possible to supply all of the compressed evaporated gas to the high-pressure natural gas injection engine, some of the compressed evaporated gas may be re-liquefied, and some may be supplied to the high- have. For this, a re-liquefaction line (RL) and a gaseous fuel supply line (GSL1) are provided from the downstream end of the multi-stage compressor (100).

The high-pressure gas injection engine E1 may be, for example, a propulsion engine of a ship, and may be an ME-GI engine, which is a low-speed two-stroke high-pressure natural gas injection engine, have.

The ME-GI engine requires a gas supply pressure of about 150-400 bara (absolute pressure) depending on the load. When the ME-GI engine is provided, the multi-stage compressor described above is connected to the compressor, As shown in FIG. 2, five compressors 110a, 110b, 110c, 110d, and 110e and intermediate coolers 120a, 120b, 120c, 120d, and 120e may be provided.

Meanwhile, the system may further include a fuel supply unit 400 that receives LNG from the storage tank, compresses and vaporizes the LNG, and supplies the LNG to the high-pressure gas injection engine. Since the fuel consumption of the engine is higher than that of the BOG due to the high power consumption and the engine load and the BOG generation amount, So that the LNG stored in the storage tank can be supplied as engine fuel.

For this purpose, the fuel supply unit 400 includes high-pressure pumps 410a and 410b that are supplied with LNG from the LNG storage tank and compress the high-pressure gas injection engine E1 to the fuel required pressure, for example, 150 to 400 bara, And a vaporizer 420 for supplying compressed LNG to the vaporizer 420. Compressed and vaporized LNG via a high-pressure pump and a vaporizer is supplied as fuel for a high-pressure gas injection engine.

However, since the gas and liquid can not be distinguished from each other in the supercritical state, the expression 'the compressed LNG is vaporized' means that the compressed LNG is supplied with thermal energy to increase the temperature (or, in the case of a supercritical state with a high density, State) can be meaningful.

On the other hand, in addition to the high-pressure gas injection engine described above, a low-pressure gas injection engine E2 for supplying gas of different pressures as fuel may also be provided, and the compressed gas compressed from the multi-stage compressor may be supplied as fuel . For example, such an engine may be supplied with compressed low-pressure compressed gas through only a part of the multi-stage compressor 100.

The low-pressure gas injection engine is provided with a fuel gas of about 3 to 15 bara, for example, to drive the generator by the driving force of the engine to obtain electric power, to drive the propulsion motor by using the electric power, The DF engine may be a DF engine installed in the ship so as to operate the engine. The DF engine can receive the compressed gas compressed through the intermediate stage of the multi-stage compressor, for example, the three-stage compressor and the intercooler, through the supply line GSL2, decompress the compressed and vaporized LNG from the fuel supply unit, .

The fuel supply unit 400 includes a pressure reducer 430 provided downstream of the carburetor 420 to reduce the pressure of the compressed and vaporized LNG to a fuel required pressure of the low pressure gas injection engine, And a heater 440 that heats the fuel to the fuel-requiring temperature of the injection engine. The LNG fed through the pressure reducer and the heater can be supplied to the low-pressure gas injection engine E2. The fuel supply line LSL of the fuel supply unit is branched to the first line LSL1 supplied to the high pressure gas injection engine and the second line LSL2 supplied to the low pressure gas injection engine at the downstream of the vaporizer. On the other hand, as shown in FIG. 2, the cooling line CL for BOG cooling in the above-described inline mixer may also be branched from the upstream of the high-pressure pump of the fuel supply line LSL.

When the compression of the LNG supplied to the DF engine and the control of the methane content of the vaporized LNG are required, a separator (not shown) for increasing the methane content by removing heavy hydrocarbons (HHC) having 2 or 3 carbon atoms may be further provided.

Meanwhile, since the ME-GI engine and the DF engine are engines capable of supplying oil as well as natural gas, an oil supply line (OL) for supplying oil to the engines can be additionally provided.

As described above, in the system of this embodiment, the evaporation gas can be used as fuel for the in-vessel engine or can be re-liquefied and returned to the storage tank for storage. Therefore, the amount of evaporated gas consumed by the GCU, And the evaporation gas can be re-liquefied and processed without the need to provide a re-liquefaction device using a separate refrigerant such as nitrogen. Therefore, it is possible to prevent the waste of fuel, and to operate the system so as to treat the evaporation gas as variously as necessary, and to maintain the part of the system, the evaporation gas can be treated in other parts, Can be processed.

In particular, it is possible to keep the temperature of the BOG which is the refrigerant at the low temperature constantly during re-liquefaction, thereby improving the re-liquefaction efficiency and maintaining the re-liquefaction performance constantly, thereby enabling stable system operation. Also, by applying an inline mixer upstream of the gas-liquid separator and retrofitting the existing re-liquefaction system, this system can be widely used for improving the performance of the existing re-liquefaction system.

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

T: Storage tank
100: Multistage compressor
200: Re-
300: Inline Mixer
400: fuel supply unit
E1: High-pressure gas injection engine
E2: Low pressure gas injection engine

Claims (10)

A multi-stage compressor in which a compressor and an intercooler are alternately provided to supply and compress BOG (Boil Off Gas) generated from a storage tank of a ship storing LNG;
A re-culling unit for cooling the compressed gas compressed in the multi-stage compressor by heat exchange with uncompressed BOG to be supplied from the upstream to the multi-stage compressor, and reducing the pressure to liquefy; And
And an inline mixer provided upstream of the multistage compressor and the re-culling unit for supplying BOG generated from the storage tank and injecting LNG supplied from the storage tank to cool and supply the LNG to the re-cure unit. The apparatus according to claim 1, wherein the remapping section
A heat exchanger for cooling the compressed gas compressed in the multi-stage compressor by heat exchange with uncompressed BOG to be supplied to the multi-stage compressor from the upstream side to the multi-stage compressor;
A decompression device that receives and decompresses the compressed gas cooled by the heat exchanger; And
And a gas-liquid separator for receiving the compressed gas decompressed from the decompression device and separating the compressed gas by gas-liquid separation,
Wherein the BOG cooled in the inline mixer is supplied to the multi-stage compressor through the gas-liquid separator and the heat exchanger. The method according to claim 1,
Wherein the compressed gas compressed from the multi-stage compressor can be supplied to a high-pressure gas injection engine provided in the ship. The method of claim 3,
Further comprising a fuel supply unit that receives LNG from the storage tank, compresses and vaporizes the LNG, and supplies the LNG to the high-pressure gas injection engine. 4. The fuel cell system according to claim 3, wherein the fuel supply unit
A high pressure pump that receives LNG from the LNG storage tank and compresses the LNG to a fuel required pressure of the high pressure gas injection engine; And
And a vaporizer for supplying compressed LNG from the high-pressure pump to vaporize the vaporized gas. 6. The method of claim 5,
And the compressed gas compressed through a part of the multi-stage compressor can be supplied to a low-pressure gas injection engine provided in the ship. 7. The fuel cell system according to claim 6,
A decompressor provided downstream of the carburetor to decompress the compressed and vaporized LNG to a fuel required pressure of the low pressure gas injection engine; And
Further comprising a heater for heating the LNG decompressed by the pressure reducer to a fuel-requiring temperature of the low-pressure gas injection engine,
And the LNG passed through the pressure reducing device and the heater can be supplied to the low pressure gas injection engine. A first stream for repeatedly compressing, intermediate cooling and compressing BOG (Boil Off Gas) generated from LNG stored in a storage tank of a ship;
A second stream for compressing the BOG from the first stream by heat exchange with the uncompressed BOG to be supplied to the first stream from the storage tank and decompressing and liquefying the BOG; And
And a third stream for supplying LNG from the storage tank to the uncompressed BOG to be heat-exchanged with the second stream for cooling. 9. The method of claim 8,
A fourth stream for supplying the BOG compressed in the first stream to a high-pressure gas injection engine provided in the ship; And
And a fifth stream for supplying a BOG compressed through only a part of the first stream to a low pressure gas injection engine provided in the ship. 10. The method of claim 9,
A sixth stream for pumping the LNG from the storage tank, for compressing and vaporizing the LNG to supply it to the high pressure gas injection engine; And
And a seventh stream branched from said sixth stream to decompress and heat the compressed and vaporized LNG and supply it to said low pressure gas injection engine.

Images